This could mean in the Drake equation ne -number of planets capable of life- is very small. A planet has to be hit with a comet big enough to deliver a large amount of water but not so big or fast to destroy it. And be in the Goldilocks zone of the star. Also the mass of the planet would play a part - gravity of more massive ones would be more likely to capture a comet. But again, too massive and I could see that hampering life.
The Drake Equation is filled with assumptions, like life must appear on a planet in the Goldilocks zone of a star. The whole equation has only one datapoint to extrapolate from. Tweak the equation's parameters and it will predict universes that only have one civilization per galaxy or worse! We have no way of knowing what those parameters are because we haven't seen other examples.
A major reason we are interested in Europa is because it might have underground oceans. Hypothetically, through tidal forces with Jupiter, the moon's core is hot enough to create oceans under the ice crust. Combined with hydrothermal vents you have the possibility for deep sea life similar to our own deep oceans. The Drake Equation does not predict this possibility.
The equation itself makes no assumptions. But anyone trying to calculate something with it must.
The last five factors in the equation will be filled in by assumptions based entirely on one data point, life on Earth. From your link:
ne = the average number of planets that can potentially support life per star that has planets.
fl = the fraction of planets that could support life that actually develop life at some point.
fi = the fraction of planets with life that go on to develop intelligent life (civilizations).
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = the length of time for which such civilizations release detectable signals into space.
Can you define any one of those without assumptions, in a scientifically proven way?
One approach is to give each variable a probability distribution. The greater our uncertainty about possible values, the wider the bell curve.
Drexler and colleagues did that, and found "a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively). ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable."
A probability distribution describes how likely different outcomes are.
It requires multiple observations or an assumed model that can represent variability.
Which is why they set very wide ranges on the things we know little about. Doing that is less unjustified than guessing specific values, as people have usually done.
It's nowhere near a precise estimate of the probability of life. What it mainly shows is that the Fermi "paradox" is no such thing. It can look that way if we guess specific parameter values, but if we fully account for our uncertainty on the various parameters, then the result is a decent chance that we are alone, given the knowledge we have so far.
I’m not saying precise. I’m saying it isn’t even an estimate.
You can’t have a distribution with one data point.
It’s similar to the arguments about 3I/Atlas being an alien spacecraft because it’s so ‘weird’.
With so few data points, everything is fundamentally ‘weird’ - or normal - we have no way to tell, so making any sort of statistical argument about it is fundamentally useless and misleading, as statistics is based on groups. And we don’t have a group yet.
We know a lot more than the simple fact that civilization exists on our planet. See section 3 for how they estimated the parameters.
One of the most uncertain parameters is the rate of abiogenesis events per planet. For that one they used a log-normal with a standard deviation of 50 orders of magnitude. They discuss specific theoretical limits from biology for both ends of the range.
Compared to this approach, the usual method is to just pick particular values out of a hat. This paper at least improves that by directly representing our vast uncertainty for some of the values.
It doesn't tell us how many alien civilizations there are. But it does tell us the range of possibilities, given what we know and don't know.
If your level of uncertainty is infinite then you're suggesting that abiogenesis could be happening every day in your back yard. I think you might admit we're a little more certain than that.
Life, once established, is about competition for niche resources. Established life would kick the polypeptides out of a protocell quite easily (with certainty > 99%).
Protocells could be evolving right now at vents in the ocean, with zero of them managing to escape their birthplace due to being outcompeted by things with fully developed organelles.
How many planets are there, and what proportion of them have detectable life?
The f does not have to be structured as fl->fi->fc, although we can see why you'd assume that kind of structure. It's simple to calculate the PI(series) when the model is just a funnel. Like the Million Dollar Money Drop gameshow.
But you could imagine a more complex model of probabilities that branches and merges. There could be events on the bayesian tree that amplify downstream events. For instance, suppose there is some pathway that if reached will leave certain minerals that future civilizations could use. This has happened already on earth at least once: lignin bearing plants could not be easily digested for a long time, and that led to coal formation during the carboniferous period.
You could imagine many such potential trees, but we only have one iteration.
It does assume that life must be associatable with a planet. It's a plausible assumption, but you could also hypothetically have life develop on a star itself or its remnants, comets, clouds of interstellar gas. Maybe even something more exotic than that (dark matter? some weird correlated statistical properties of the quantum foam?)
About forty years ago I read a terrific book about life forms that live on a star. Maybe Starquake was it called? Did to the abundance of energy on the surface of a star, they live their lives a million times faster than humans. Thus for both them and the humans who discover them, communication is difficult. I think the humans push these life forms to develop civilization, which from the human's perspective had them go from primitive animals into sophisticated beings of technology past their own in something like a day.
The cheela lived on the surface of a neutron star, and they lived faster because the nuclear physics that powered their metabolism are far faster than the chemical and mechanical physics that power our own.
I'm not against piracy, and I love Anna's Archive... but publicly linking directly to a pirate source for something like this seems wrong. Could've just linked the Wikipedia page and let people acquire however they prefer.
Anyway, sounds interesting, gunna add that to my list
Well I don't really have a line, but that doesn't mean I'm going to go linking directly to such sources in public - not everyone agrees with my stance on copyright. Those who do can easily go find it themselves.
Also Macbeth was written 400 years ago. Let's not pretend this is a fair comparison. This author has been dead only 20 years - it might be that their partner is still alive and needs that money, or their children.
What a strange way to phrase it, considering in your last comment you were talking about how copyright expiry is exactly for this purpose.
Anyway, what is copyright expiration in America these days? 100 years?
Also, is it simply a matter of X years after creation? I somehow doubt it's that simple anymore. I wouldn't be surprised if "copyright is extended indefinitely if the work is being actively commercially used" or some such
Which is saner eh! That way people living at the time who are protecting it (copyright and patents are both protections for things otherwise being distributed and which could be copied easily) can benefit from it eventually.
My initial reaction was the same, then I thought: "no, we need more of this".
We need more discussion about copyright in our society, and we need it most in front of those who are unaware, inattentive, or would otherwise shirk that discussion. Posting a relevant link in a relevant discussion appears as good an avenue as any to get people talking.
Promoting copyright infringement in order to initiate a conversation about copyright is about as moral as murdering civilians to initiate a conversation about human rights.
I was bothered by the nearly a-scientific-ness of PHM. The story was nicely done in general, but it feels like he pretends to be hard science fiction when he's really Star Trek-level.
Thanks, I read that part before I shared it. It's pretty clear to me, these are pretty well defined quantities, just hard to measure. What is unclear is perhaps the definition of life. But at no point does it assume a planet must be in the Goldilocks zone. So perhaps you want to point out those assumptions you are talking about to me, because I don't see them.
Edit: the parent post has been edited substantially after I replied.
> these are pretty well defined quantities, just hard to measure.
They are "defined" conceptually, in words, not in physical quantities. It assumes we can assign a known value to any of that when we don't and likely never will. It's like saying "Let X answer the unanswerable question. X is the answer".
> at no point does it assume a planet must be in the Goldilocks zone
You could say it implies it with fl.
> Edit: the parent post has been edited substantially after I replied.
I can't, but the equation itself doesn't to that. The assumptions are up to the reader to make. That's why I think that the equation isn't particularly useful.
That's just your interpretation. Take the equation at its face value and it does allow for life originating around some deep sea vents, like JamesLeonis speculated.
Yes, but we should consider these linkages when setting values. If we assume that volcanic vent life is very unlikely to become spacefaring, we should either leave it out of the "life" term, or leave it in but lower the probability of the "becomes spacefaring" term.
It goes the other way around. The Goldilocks zone is a shorthand attempt at helping us guess how many planets out there are capable of supporting life.
Even if you only had a handful of civilizations, the sheer time that has passed and size of the universe should mean that life should still be alot more apparent.
With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
Another point I feel is that proliferation of life should be an self-reinforcing affair, for intelligent life even more so. A spacefaring nation may terraform or just seed planets, and these in time will replicate similar behaviors. At a certain point, a galaxy teeming with life should be very hard to reverse given all the activity. A life itself isn't necessarily evolved from biology, AI machine lifeforms should also well suited to proliferate, yet we don't see them anyways.
At some point replicative drift will set in. How many replications is two million years? How long before the probes evolve? How long before they speciate? How long before a species turns on itself?
> Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
Time, not space, is your answer here.
Two reasons -
(1) civilizations might not survive long enough to do this.
(2) 13 billion years is a long time. So you have the reciprocal of that as the chances to be in the right year to see such a probe. And with results from the new telescope we now have hints that the 13 billion number is bogus, the universe is likely far older.
> With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
What are the incentives to build and deploy such a thing though? We as a civilization fail to fund things that have a ROI of more than a few years, how are you going to fund something that pays off after a million year?
Exactly. Some of the biggest explanatory factors for the Fermi paradox are likely to be economics and politics: interstellar travel is unreasonably expensive, unimaginably slow, and has negative ROI unless your time horizons are beyond anything that's ever been used on Earth.
Consider that in some countries on Earth, we can't even get consensus that obtaining energy directly from the Sun via solar panels is a good idea.
Also, people vastly underestimate how hostile space is: colonizing Mount Everest, the Antarctic or the continental plateau under sea would be far easier than colonizing Mars. And Mars is the most hospitable extraterrestrial place we know of.
I don't think we would colonizing Mars, free floating colonies akin to O'Neil Cylinders orbiting Earth would probably be the more logical option. And with increasing robotic automation capabilities, it's not improbable to see these being built in the future.
"Extremely improbable" would be a better assessment.
Even ignoring the project complexity, difficulty, and energy budget, which can't simply be handwaved away by "robotic automation", one reason is simply that such colonies don't solve any problem that we're likely to have, that can't be solved much more cheaply, safely, and effectively.
But even the idea that we'll eventually have the technology to build such structures is debatable. Will this be before or after we solve climate change, for example? Because that issue is likely to severely impact our technological capabilities over the timescales involved. And as of today, the most technologically advanced nation is doubling down on atmospheric carbon production.
Having the technology to build it isn't the hard part. The question is why you'd do that in the first place and who would fund such a colony.
First of all it's going to be massively more expensive than any housing we've ever built on earth so only a very small elite could afford living there.
But then again, space is a very hostile environment: it's super dangerous (any incident will almost certainly snowball into a dramatic accident), very unhealthy (billionaires are currently funding longevity research, so I don't think they'd like to go in a place where they would age up significantly faster than on earth…), and life is just worse up there on all respect…
FYI just about every outer solar system moon or planetoid has a liquid ocean somewhere underneath. Europa is neither exceptional or even that interesting anymore.
The fundamental problem with the Drake equation is that it's frequentist, not Bayesian
Hence why you get too high sensitivity to parameters you have no way of having an estimate with a small margin of error
We "don't care" about how many civilisations are out there, we care to the point where we can interact with them.
As mentioned, it has several assumptions. "Rate of birth of sun like stars" means nothing. You can "always" have an exception for life that will throw the data off: "star too bright but with a hot Jupiter tidally locked in front of your moon, shielding it" etc
I don't see any reason to believe that giant impact is the only way to get life-supporting amounts of water. We know Mars had liquid water. We know Titan has lots of ice. We're pretty sure Venus at least had noticeable amounts of water. Did all of these come from Theia-type impacts? I don't think we have any evidence of that.
Multiple impacts is the standard hypothesis for a source of Earth's water. If I recall correctly, outgassing from volcanos is another source.
Keep in mind, the solar system formed from a relatively homogenous nebula. It was the formation of the sun that forced lighter elements to migrate outwards, and that only happens if the lighter elements aren't already part of a larger object. There isn't much of a difference between a 10 km chunk of ice and a 10 km chunk of iron gravitationally speaking. Bouancy doesn't play a role here, so density doesn't matter. Outgassing does matter, but that is a slow process for large object, like the Earth, or for smaller objects on Earth crossing orbits that don't get too close to the sun.
It's also worth considering that each planet's situation is unique. There is much more water ice on the moons of the outer solar system because there was more water at the time of formation and the lower temperatures mean the water that was there stayed there. As for Mars, even though it is colder than the Earth, it is much less massive. As such, its atmosphere bleeds away lighter molecules (never mind lighter elements).
> Multiple impacts is the standard hypothesis for a source of Earth's water.
Right, which is why it's baffling to me that everyone in this thread seems to be losing their mind over this result, thinking it affects the Drake equation and rewrites solar system dynamics. The multiple impacts thing might not have actually happened to earth, but there's still no reason to believe it wouldn't work.
Yep, mega-impact is a classic example of an ad-hoc hypothesis. For example, Moon formation is much better explained by multi-impact hypothesis, which also requires less assumptions.
Dang, I can't post anything in this thread without someone thinking I agree with them that science is BS. Giant impacts aren't actually surprising in an early solar system that hasn't hit steady state yet. If multiple impacts better explain all the evidence for Theia, including the weird patterns of isotopes and possible fragments deep in the mantle, that's news to me.
I recently became addicted to the SpaceSimsx and SimulaVerse. My takeaway is that so many just slight deviations can extinguish life on earth. I used to think of possibility of life in other worlds just in the lens of statistics. There are so many combinations and possibilities that it seems inevitable. But seeing just how perfectly aligned our solar system is makes me really reduce the probable number of chances of other habitable scenarios in my mind.
These channels helped me realize just how important all the planets in the solar system are to our continued existence. Its as if we have an entire family thats just perfect to make our existence possible. An entire family each one quietly doing their part without fanfare or credit.
No matter what the circumstances, live will evolve to perfectly match the conditions it is under. There are many species so perfectly adapted to their ecological niche, they are in great danger of extinction. Like peacocks, who are stuck in a local optimum with no way out.
Well, just keep in mind that its not a "perfect alignment" as this seems to prescribe some kind of intent. It's more a set of requirements that allowed life to not be extinguished so easily. We could never exist in a place where this didn't happen like this, so obviously we have to be here and not some place ealse. So its more that out of the 1 places we have seen that was made like this, we at least know life happened there.
Could a tardigrade withstand these scenarios? If the answer to any of those is yes, could we then say that even with the parameters skewed a bit, there is a chance life exists elsewhere, and under completely different and extreme or (not "normal") conditions? Is the tardigrade here as a "clue" to tell us that life could form potentially anywhere?
The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time.
e.g. Say chance of a random planet ever being hit by a water-carrying comet is one in a billion, then with 100B - 1T planets in the milky way it'd happen here 100-1000 times. If chances are only one in a trillion, and we're the one in the milky way, then there are still another 100B - 1T galaxies out there and therefore a similar number of such events.
And you have to have multiple low probability events. These probabilities multiply.
We had a good start. A Jupiter to clear the debris, a Theia impact to create tides and contribute to tectonics, a magnetic core, a shielded atmosphere. We had water delivered to us. Maybe even panspermia.
Maybe cell walls and mitochondria are hard. Maybe multicellular is hard. Maybe life on land is hard. Building lungs, rebuilding eyes, having actual energetic gasses on land...
Maybe life is easy, but intelligence is hard. Maybe civilization is hard.
Maybe technology development can only happen on dry land, because aqueous chemistry is hard in water. Sorry mollusks and cetaceans: you'll probably never be able to do chemistry or materials science.
Maybe you need water and carbon and other chemistries aren't robust enough.
Maybe you need lots of fossil fuel deposits to develop industry. And that requires growth without bacteria and decomposers for millions of years, implying a certain order to evolution.
Maybe you need a certain sized gravity well to escape.
Maybe surviving the great filter is hard and still ahead of us. Maybe every species can build tech where a kid in their garage can extinct the entire species by 3d printing grey goo.
There's just so much we don't know about how life could happen. Let alone intelligent life. We don't even know where we're headed.
My pessimistic side says that the conditions for intelligent life are so implausible that we’re unique, and when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
Basically I fear we’re the universe’s only shot of appreciating and populating the galaxy (or beyond) and we’re on the brink of throwing that away.
> when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
There will be no successor civilization to humans. Earth won't be able to support multicellular life in a few hundred million years due to the sun becoming gradually more luminous over time, resulting in higher surface temperatures that will eventually culminate in a runaway greenhouse happening, as it already has on Venus. Due to human-driven climate change effects this event will certainly happen much sooner (<100m years) as well, which is simply not enough time for another intelligent species to evolve after a large-scale extinction event.
Even if life evolving on earth was an incredibly rare event the chance of such circumstances not happening elsewhere even in our own galaxy is infinitely small - there are trillions of planets and 100b+ stars. On top of that there are 100s of billions of galaxies within the observable universe as well.
> Due to human-driven climate change effects this event will certainly happen much sooner (<100m years) as well
No, it will not. Human driven climate change is drastic, but the Earth has seen far worse events than our anthropogenic carbon emissions. For instance, the Chicxulub impactor at the end of the Cretaceous changed atmospheric conditions overnight, and to a much greater degree than whatever we have cooked up. It was the equivalent of detonating the world's entire nuclear arsenal about a million times over.
Sure, it finished off the dinosaurs. But 66 million years later, we, the descendants of tiny rodent-like mammals, are still here, as are the dinosaur's own descendants, the birds.
Additionally, during the Carboniferous about 300 Mya, both carbon dioxide and oxygen levels were considerably higher than they are today, and life actually thrived. I would say that with the increasing luminosity, there will be at least a decent period on Earth where life returns to that sort of diversity. We are actually still only in an interglacial of an ice age—this has effectively sterilised large tracts of our planet by covering them with ice sheets, or locking permafrost into the soil and making them unavailable for large trees.
Let me be very clear: our emissions—if unchecked—will make life very difficult for us as the rising seas and temperatures scatter millions of people out of coastal cities in the tropics further north and south and cause war, division, strife, and discord like we have never yet seen. But actually bring forward the planet's overall demise? Nearly impossible.
Let's not have the hubris to think we puny humans could remotely affect the planet's geological timeline. If we somehow all disappear simultaneously, most direct evidence that we ever lived will disappear with us–perhaps within a hundred thousand to a million years of erosion and weathering. Our emissions will similarly lurch to a halt and will reach equilibrium within a similar time span. That's all it takes to remove our direct creations from the geological record.
> There will be no successor civilization to humans. Earth won't be able to support multicellular life in a few hundred million years due to the sun becoming gradually more luminous over time
Modern humans have only been around for < 1 millions years, and all the technology we have invented is incredibly recent. 200 years ago we had neither electric light or bicycles.
Over the course of 100s of millions of years, as the sun's increasing luminosity becomes an issue, I'd have to assume we could create some sort of atmospheric solar shield to reflect or absorb a lot of the energy. Of course you can only postpone the inevitable (red giant).
Assuming the evolutionary lineage of our species survives a few hundred more million years (which seems rather doubtful), then it's not going to be homo sapiens any more - we'll have evolved into successor species that may be barely recognizable. If you go BACK in time 100M years, our ancestor was some mouse-like animal.
As long as we have air and water (i.e. as long as we're alive), then we can make propellants such as Methane or Liquid Hydrogen and LOX, Hydrazine & Dinitrogen Tetroxide (or Hydrogen Peroxide).
"and when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet."
Successor. Whoever comes along after we've done ourselves in.
> ...when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
On the flip side, that could also be plausibly a blessing, avoiding them to fall into the same trap of becoming too powerful before they get wise. These comics illustrate it: https://www.badspacecomics.com/post/grounded
Even on Earth, the only reason humans exist is because the “local maximum” of the dinosaurs was wiped out by a meteor. Perhaps comparably intelligent dinosaurs would have eventually evolved - but it’s not a given!
Dinosaurs existed for some 200 million years with no detectable signs of technology development[0]. Presumably, the steady state did not produce a scenario in which the intelligence niche would develop without some other less catastrophic global change event.
Intelligence evolved at least three times on earth - dinosaurs (leading to corvids, but a raptors already intelligent), mammals and cephalopods (e.g. octopus).
I suspect that any evolutionary environment will eventually create enough variety and instability that some generalists emerge, creating a reward for intelligence. The rise in intelligence from early water-bound life to later forms was likely all driven by more complex and diverse environments.
Maybe they didn't produce an intelligent species just because they had not the luck of living in the unprecended time in the history of Earth with both high atmospheric O2 and very low atmospheric CO2 we enjoyed for a while, before we started to burn fossil fuels by the gigaton. See https://www.qeios.com/read/IKNUZU
It took several environment-changing events to get our unique kind of intelligence; mammals had to thrive in place of saurs; and then, Africa needed to be split by the Rift and to create the dry savannah.
This forced some apes to climb down the trees and depend on a diet of scavenging for meat, which happened to both increase brain size AND require improved intellect to survive, forcing the evolution of our hypertrophied symbolic brain.
Had this not happened however, other intelligent species could have filled the niche. There's no shortage of other intelligent species in our planet, not just other mammals but octopus and some birds. And then you get hive intelligence, which could equally be forced to evolve into a high problem-solving organism.
You're not wrong, but you're in the wrong place to talk to people about low-probability events and how they multiply. Most Hacker News can't into elementary-school-level probability equations and will instead take the ostrich approach; there was some behavioral scientist dude from Cambridge Analytica who wrote about this and the TL;DR is that most "adults" have infantile minds that prefer various safety blanket mechanisms that society is more than ready to offer them just to do anything to have an excuse to not face the truth of what basic math reveals to more likely than not be true.
There’s not a huge difference between zero and one, other than whether someone’s around to comment about it on HN. And even a second wouldn’t really tell us more about the probabilities.
Just as easily as we can multiply planets times systems times galaxies times cluster groups we can multiply multiple small probabilities of each chemical being present at the right time and right type, temperature ranges, gravity ranges, etc
If the numbers you propose turn out to be accurate then the odds of there being other life are near zero because even 1/1000 planets are not habitable likely.
Huh? Even in the 1-in-a-trillion case, there's still maybe 1 trillion galaxies each with one planet that was struck by a water bearing comet, so even if only 1/1000 of those are otherwise habitable, that still leaves a billion habitable planets in the universe with water.
I doubt water (H2O) is actually that rare. The most common elements by far, both in our own galaxy and the universe as a whole, are Hydrogen and Helium, but the next two most common are Oxygen and Carbon.
At the moment, rapid and massive expansion seems likely with tech only just on the horizon.
Enough AI and robotics for an autonomous factory may be a mirage (such mirages have (metaphorically) happened before), but it seems like it's on the horizon.
Even with relatively mundane growth assumptions, that can go from "species inventing writing" to "Dyson sphere completed, is now sending out seeds to every accessible galaxy" on significantly less than the timescale of light crossing a spiral galaxy's disk.
I think its the fact that if we really wanted to, we could probably make it happen already today. On a scale of a couple hundred million years, its possible we could reach most of our own galaxy, which is a small slice of time in the life span of the Milky Way. So the question remains, why hasn't this already happened, or has it?
Galactic colonization, carried to saturation, would detectably modify the appearance of a galaxy. So called "type 3 civilizations" would convert a significant fraction of starlight to lower grade heat, which would be radiated. Searches have been conducted for this signature, with the result that no more than 1 in 100,000 galaxies has such a civilization, and with the result being consistent with none.
This is interesting speculation, but it adds one more completely unknown variable to the Drake equation.
What’s the probability that a radio-capable civilization becomes a galactic type 3 one? Looking at the only example we have, it appears very unlikely. It seems much more probable that we’ll destroy ourselves within the next centuries.
I am not an astrophysicist but I have a hunch any speculations of galactic colonization fails to entertain just how big space actually is. I feel like there is ample reason to suspect the probability of galactic (or even interstellar) colonization is exactly 0, and no civilization in the history of the entire universe will ever colonize an entire galaxy (and probably not even more than a handful of solar systems outside their home world; if any).
Your argument shows a lack of understanding of exponential growth.
Any given colony has to create only slightly more than 1 additional colony in order to drive exponential growth. There doesn't have to be any coordinated action by a central authority for it to happen. For it not to happen (if it is physically feasible), in contrast, every species has to refrain from doing it at all points in their history, almost without exception. And those that do the colonization will seed additional colonies with a mindset that led to colonization; such mindsets will be selected for for further expansion.
Permanent exponential growth is very rare in nature, and even rarer in biological systems. What we observe as exponential growth is usually only a partial observation of a logistical curve or is missing a system collapse at the end of the curve.
We have no reason to believe alien (or even human) civilization will continue to grow and expand forever. Heck even the human population curve has started to slow down and is now revealing it self to be a logistical curve.
But regardless of this, space is very very very big. And there are a lot of extremely hostile worlds out there. Any civilization will experience biological limitation to which worlds they can (and will want to) colonize. Likewise they will experience both economical and physical limitations to how far they will send their machines. Lets say an alien species is lucky and has a habitable world inside their solar system which they will colonize. I think this is likely. They also spot another world in a nearby solar system which takes them 200 years to travel to, eager colonists travel in a generational ship, and 600 years later the colony is thriving. Now they run out of nearby habitable worlds. There is a world of questionable quality 500 years away and they are unable to persuade enough people to fill a generational ship. Also they learned the stories of the passengers in the generational ship, their lives kind of sucked, we have it much better on this world. So it is better to just stay here. This might happen after 1 or 100 successful colonizations, but I think space is so freaking large, it will happen to all civilizations. At some point they will run out of worlds to colonize, and they will never expand far outside of some local area near their home world.
Unless some means of communicating faster than light is found a galactic colonisations is not a civilisation, its multiple ones. A colony ship heading in one direction at 0.1c will never interact with one heading the other way at the same speed. After 10,000 years the civilisations will be very different, after 100,000 years they will barely be the same species.
Even if 99% stop and fail, the 1% will continue and continue expanding.
The only way to stop would be to run out of planets, which would mean every habitable planet and star system has been populated. There wouldn’t be a biological urge to stop, as the successful colonies are ones which have the urge to expand. An environmental need wouldn’t affect every colony and ship short of a galaxy spanning event of some sort which we can’t even conceive.
Yes, I think that will never happen. My prediction is that generational ships are super rare in the universe, and may only happen ones or twice in the entire history of a civilization, and for a tiny portion of civilizations. Meaning by far majority of all civilization will have zero generational ships. Maybe a single civilization somewhere in a distant galaxy will have hundreds, but nowhere near enough to cover an entire galaxy, not even if we count decedent civilizations.
I also think fast space travel (like 0.1c) is rare among civilizations, and may only happen in the order of hundreds of time in the history of some civilizations. And most of these fast space travel will scientific instruments for curiosity and exploration, not for colonization. And that a technologically advanced civilization would favor doing their explorations with telescopes, not probes. So probes would only be sent long distance for rare occasions.
This would mean that almost no civilizations will be expand beyond their solar system, and those that do, will only do it a handful of times, and the expansion will finally stop.
It doesn’t matter how rare it is to get started once it starts. Every ship is a new civilisation that is created, one predisposed culturally and perhaps genetically to spreading out.
Especially once you reach the “hundreds” level then given the technology exists and the people exist why would it stop, until there’s nowhere else to go.
There is the light cage issue where a civilisation can only spread so far with exponential growth before internal pressures overwhelm it (the leading edge never gets a chance to continue as it is overwhelmed by trailing edges)
Even in that situation though you’d still have self replicating probes - likely at a far lower tech level than biological. Once you reach the tech to send one probe which can duplicate itself more than once using resources in a new system then its game over.
Send 50 probes to each of the 50 stars within 15 light years at 0.01c. If 10% make it they then use local materials and send 50 more, that’s 250 out in 1500 years. Then it’s 1250 out in 3000 years. Within a few millennia years you’ve got millions of probes spreading in an unstoppable way. The ones heading back “inwards” will fail, but those heading outwards will reach each new star dozens of times, only one will need to get there. Within 10 million years you’ve reached the entire galaxy.
To stop it you’d have to make a self replicating probe which was faster and did exactly the same thing and caught the earlier probe, but then when would that probe itself stop, it would have no way of knowing if there were any other “bad” probes to find without becoming the bad probe itself.
Living beings are the same. Once a few dozen have made it and passed on, it’s inevitable it will continue. It may leave out a hollowed husk in the origin point with all resources having being consumed in the centre, but that doesn’t matter as the centre has no way of affecting what happens on the edge, and one edge has no way of affecting another edge.
von Neumann probes are a fantasy. I see no reason why any civilization in the entire universe will ever build a successful self replicating probes, let alone ones that are still replicating dozens of millennia later. The reasons include that targeted probes and telescopes can give you pretty much the same amount of knowledge for far cheaper and much quicker then random walking probes across the galaxy. There is also a technical limitation to self replicating probes, even if a civilization will build one, we cannot expect the self-replicating mechanism to last dozens of millennia. Some generations will fail to replicate, and in the vastness of space that may mean the entire lineage will go extinct.
I think you may be expecting an exponential growth when population dynamics almost always favor logistical growth. At some point your machines, or your colonial behavior hits a limit and your growth starts to slow down. I suspect that limit is within the solar system for the vast vast vast majority of civilization. And even if one escapes their own solar system and starts anew on a new home world, they most likely will not colonize another. The space is just so big, and habitable worlds so far away from each other that I find it extremely improbable that any civilization (and their ancestor civilization) will survive more than 5-6 colonization (by far most will see 0).
> Living beings are the same.
They are not. You are describing living beings like viruses (fair enough; viruses are worthy to be considered lifeforms) that spread from host to host until they infect everybody. But viruses don‘t behave like that. The vast majority of them only infect their closest neighbors, and those that do spread towards the limit of all members of the species (like Covid) still fall short and eventually start to slow down their spread in a logistical manner. Growth only looks exponential while you are at the initial stages of spread. This behavior is not only common among viruses, but in fact most population dynamics can be described with logistical growth.
Yes, theorizing a future possibility that has no president is, by definition, fantasy. I mean, you can do fantasy, it makes good science fiction, but until we have evidence that von Neumann probes exist and are capable of colonizing the entire galaxy, it remains fantasy. Theoretically we could build a high speed rail between Seattle and LA, we could build a permanent settlement on Antarctica, and we could replace our jet-planes with hydrogen powered flying wings, but until we do, a world with those things are just fantasy.
The only argument for von Neumann probes that I can think of is as a specific answer to the Fermi paradox. The universe should be filled with these probes, but since it obviously isn’t, we can infer that no civilization has reach the interstellar age.
I reject this framing, the Fermi paradox is only a paradox if you assume that space colonization is a thing that is not just possible, but inevitable. My solution to the Fermi paradox simply rejects this assumption. Civilization will not colonize definitely, they will do their space explorations with telescopes and targeted probes, and they won‘t build any von Neumann probes (at least not ones continue to replicate for dozens millennia).
Aside: I am aware of the irony that my description of civilizations outside of our solar system is also a fantasy.
It's rare in biological systems because it's terminated by running out of some resource.
But you're saying galactic colonization would terminate without running out of new systems to colonize.
There would be a slowdown due to geometric constraints -- only so many new systems adjacent the boundary of the colonized zone -- but that hardly solves your problem.
My speculation is that the size of space is an obvious geometric constraint which will limit the span of any civilizations almost immediately.
If we look at humans, we have both the space, technology, and the resources to expand even further on earth, yet our span only marginally larger then it was 10 000 years ago. We can have permanent settlements on Antarctica, floating on the ocean, etc. but we don’t. We can increase our population by another order of magnitude, but again, it looks like we won’t. This follows the same population dynamics as most other species on earth. I think aliens will be no different.
I guess it depends what question are we trying to ask. It may well be that there is no other intelligent life close enough to us, or coexisting with us in time, that we will ever be aware of it, but yet the universe may still be teeming with intelligent life.
In either case it's a statistical question of how common is life, and intelligent life, but of course there's the human interest in potential contact with another intelligent life form.
Hydrogen is the most common element in the universe. So long as you have elemental oxygen, it will react with things and hydrogen is the thing it will react with the most. So having water is almost a given for any Star system. Additionally, protoplanet and cometary collisions are in fact statistically inevitable. The real question is if water can be delivered at a point after enough gravity has amassed to ensure the water stays there.
Right, that's the sticky point? The likelihood of a planet in the Goldilocks zone to be too hot in the early stage of stabilizing its chemistry that it requires seeding with "post-formation" chemistry? Is that likelihood close to 100%, or maybe not even near and we were just set up for a funny cosmic event.
I agree. In addition to the chemical elements like water, as mentioned in the article, the impact with Theia also enabled strong magmatic activity at the core of the planet, and that was a critical element as well to sustain life.
Probably the strong magnetic activity of the Earth's core was key to maintaining the atmosphere, but also, the magmatic heat contributed to keeping the planet at a good temperature to support life when a young Sun provided significantly less radiation.
All these elements may suggest that the collision is needed to satisfy the very strict requirements about where the planet is located and about the size and composition of the colliding planet. This makes the probability for life-sustaining planets in the Drake equation extremely low.
As an indirect proof of the tightness of the condition is the fact that the Earth in its history had periods of climate extremes hostile to life, like the Snowball Earth when the planet was completely covered by ice and snow, or at the opposite extreme, the very hot periods when the greenhouse effect was dominating the climate.
Speaking of Drake equations, you should (1) see the other comment here with this account name (2) check out the top Pirate Bay rip of Dark City (which predated that other movie) and turn on the English subtitles and count the number of times the characters look at or make gestures pointing to certain alignments of the text in the subtitles and, if you're true "hackers", try to figure out the encrypted messages in the text alignments that the characters are looking at/pointing to at key moments – and then when/if you figure out what the encrypted messages mean, try to figure out how the director worked together backwards so that they could have a script that aligns a certain way using subtitles and then make the scenes so that the actors are looking/pointing to key spots at just the right time.
If you appreciate technical things, you'd be in for a treat.
Right. It's discouraging. We now know that many stars have planets, and some of them are even in the Goldilocks zone. But if it takes a planetary collision to get water...
And only one planetary collision, because each one wipes out essentially all life.
Look at the rest of the solar system. Mars - almost no water. Luna - almost no water. Venus, maybe water[1], but as steam. Too close to the sun and too hot.
I find it incredibly encouraging. I fear aliens existing in sufficient enough quantity to find us more than I fear Earth being the only host to intelligent life until we escape it.
Probably not the only host, but habitable planets are sparse. If Einstein was right and faster than light travel is impossible, the number of planets we can even talk to is not that large. There are only 94 stellar systems within twenty light years.
"The hypothesis that life, in the form of “seeds” or spores, is distributed throughout the universe, traveling between planets, moons, and other bodies via space dust, asteroids, comets, and possibly even spacecraft."
I want to think that the water contained life and not the barren earth.
Bit of a nit but the Drake equation is intended 'to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy' (from the Wikipedia entry for it). Nice thing is that you can drop a few terms to get to origin of life.
Don’t forget this can only happen once, really. You need it to be such a rare event that it doesn’t keep sanitizing the planet with repeated impacts, but one really perfect strike will bring what you need and allow life to form.
The number of instances where this (something unreasonably unlikely) happened in our cosmological history is kinda surprisingly high. I’m absolutely convinced there’s no advanced life (and CERTAINLY no technological civilizations) outside of earth.
One other example: we gained most of our adaptability, curiosity, and problem solving skills as very tiny mammals while dinos ruled the earth. The only way we ever took over the planet was thanks to an asteroid wiping out all those huge creatures. Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.
Our intelligence exploded largely because that extinction event removed almost all major predators, turning earth into a giant survival puzzle sandbox for mammals to grow in.
Edit: our brains only grew big because it was the best means of survival - they’re crazy expensive, so without this “sandbox puzzle” effect, we probably never would’ve grown them.
> Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.
Maybe it was just being small, puny, and having a tendency to cower in burrows was what saved us. Our ancestors may not have been much smarter than squirrels, and squirrels aren’t very bright.
Hominids brains didn’t get big until long, long after the KT extinction. A Tigers brain is not that much smaller than that of an an Australopithecus.
Correct - that’s what SAVED us. What allowed us to thrive and dominate the planet was what I mentioned.
It may be more correct to say that growing a larger brain (larger than a lizard’s, I mean) was only realistically possible because of the sudden loss of predators.
Earth has been struck by large comets many times killing the majority of life on the planet each time. In an early solar system it would be more frequent. Once a comet impacts there is one less comet out there. The solar system cleans up over time making impacts less likely over time.
Especially in the context of this, I am baffled by people who go to great lengths to prevent life from Earth arriving on other solar system bodies. Such as all the efforts to sterilize the probes.
Historically to prevent pre-contamination and erroneous biosignature readings. This may ease once we have some solid pointers or confidence there may be none (caution is likely warranted due to the gravity of such a discovery).
Consider Mars. Endless probes for 50 years going to Mars looking for life. No clue of life has ever been found. At what point do we face the fact that Mars is a dead rock?
What we should be doing is collecting samples of extremophiles from the Earth, and attaching a few packets of them to every probe going to Mars, and see what happens. Probably nothing will happen, but it's worth a try.
A brilliant summary! You've deepened the question from "Does a habitable planet exist?" to "Does a planet successfully complete the complex dynamics of life's origin?" The habitable zone is merely the ticket, while the conditions you mention are the truly demanding filters. Considering this, the probability of our existence truly seems miraculous
There is a hard limit on the number of atomic elements, and an even smaller limit on the number of soluble compounds that facilitate chemical reactions, and water is demonstrably both the best and the most common in the universe.
So while it may be possible for life to exist without water, any alternatives should be reasonably expected to be even more rare than water-based life
There's a reason life is carbon-based, and it's not random. It's the only element that works, due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable. There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy. And no other elements have any hope. If you have carbon-based life, you need water as solvent and medium.
It's a pretty safe assumption that all life requires water.
> due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable
Well, the thing is that all of those are environment-dependent.
We do have data on a somewhat diverse set of environments, and it's enough to confirm what we knew about the flexibility of carbon. But it's not enough to disprove the alternatives.
1. xbmcuser’s point:
They challenge the anthropocentric (Earth-centric) assumption — “we only know life as we know it.” Philosophically valid, but scientifically weak without proposing a viable alternative chemistry.
2. joshuahedlund’s reply:
Grounds the argument in chemistry and probability.
There are only ~90 stable elements → a finite combinatorial chemistry space.
Among possible solvents, water is the most abundant and chemically versatile (dipolar, wide liquid range, high heat capacity, good at dissolving ions and organics).
→ So even if other solvents can work (like ammonia, methane, formamide), the odds heavily favor water-based life.
3. caymanjim’s addition:
Brings in carbon’s unique valence behavior:
4 valence electrons → can form stable, complex chains and rings.
Bonds are strong but not too strong → dynamic yet stable biochemistry.
Silicon (next best candidate) forms brittle, static lattices and poorly soluble oxides → bad for metabolism.
→ Therefore: if life is carbon-based, water is the only sensible solvent.
But when you dig down deep on theories like that it just doesn’t make sense from a chemistry or physics standpoint. Everyone saw that Star Trek episode about silicon based life and ran with it as being possible. It’s just a show.
Mars is technically in the goldilocks zone of the solar system... but water on Mars boils at 0C or 32F due to low atmospheric pressure, which really sucks.
Related, a recent study suggests up to 1% of our mantle is water trapped within rock that gets released as subduction increases to higher heat and pressure. This water could account for three times the amount of water on the surface and may represent a whole-Earth water cycle.
I wonder how this ties in with the submitted link about Theia. And it will be interesting if we ever get similar trapped water discovered in martian rock.
I've tried reading the paper, which is obviously less hand wavy than this mess of a blog post but pretty tough going for a layman. I still don't see how they conclude that the water arrived all at once instead of in a bunch of comets... https://www.science.org/doi/10.1126/sciadv.adw1280
It's that. Just one more in a long line of wild-eyed 'the Earth collided with' theories.
> Scientists have shown that Earth’s basic chemistry solidified within just three million years ...
They haven't 'shown' anything. They may have evidence to support part of one model ... if they can demonstrate that a Theia probably existed in the first place.
"Today’s element abundances of the BSE and isotope constraints strongly suggest that the bulk Earth comprises ~90% PE, ~10% Theia, and ~0.4% late veneer material... Other models suggest that Earth formed from ~60% PE and ~40% Theia ..."
>a later collision with Theia likely delivered the water
Etc. If water was so hard to get ... where in the hell did this hypothetical, no evidence 'likely' get the water it 'delivered'?
I also don't see how they disprove the contribution of gravity. Remember that Earth is composed of fifty Titan-sized bodies.
Titan, and probably Uranus and Neptune, probably have their methane etc. as a result of outgassing - initially, the volatiles are embedded in the inner rocks, but as they gravitationally differentiate and heat - and are subject to tide-like interactions with other bodies - the volatiles are released.
(The real questions are "Why does Ganymede not have an atmosphere?" and "What's up with Venus, really?")
I believe the idea is that the water was all cooked out of Earth's protoplanetary disk material before it even formed large chunks. So gravity never got a chance to "contribute" on that front.
>Our Solar System formed around 4,568 million years ago. Considering that it only took up to 3 million years to determine the chemical properties of the Earth
sounds suspiciously precise. You'd imaging the proto Earth would have formed gradually over millions of years from rocks and dust merging rather than suddenly there 4,568 m years ago and then shortly after crashed into?
Well, 3 million is "millions". Anyway, that very quote continues:
> "...this is surprisingly fast," says first author Kruttasch.
So they don't entirely disagree that it's weird.
But why are you replying to me with a quote from the article I already called a mess? Try your hand at the paper if you want real answers. :D Like I said, tough going, but they sure seem to think they have the sigfigs to back it up.
>was rich in volatile elements essential for life, such as hydrogen, carbon and sulphur.
Today years old on learning that 'carbon' is a 'volatile element'. (I come to learn that astrogeology has a unique definition of volatile).
• The summary's own source article points makes no reference to carbon being volatile.
• The wikipedia article for 'volatiles' in the astrogeological sense makes no reference to carbon being volatile https://en.wikipedia.org/wiki/Volatile_(astrogeology) . Similarly, the wikipedia article for 'refractory', posed as the astrogeological opposite of volatile, does not place carbon at all in the spectrum of volatile to refractory.
Thank you, that does make me feel at the same time better as an individual and sadder about my expectations for the astrophysicists’ ability to draw anything resembling reasonable conclusions about the makeup of the celestial bodies.
Interestingly, Earth scientists have long understood that plate tectonics is highly unlikely to exist on a rocky planet without water (to put it simply, water is needed to deform the Earth's upper mantle), given all that this entails. If this hypothesis is true, plate tectonics as such should be post-collision.
The article says the light elements hydrogen, carbon and sulfur (and oxygen?) were only able to condense on the outer planets (and their moons). And the original article specifically says "the inner Solar System planets Venus and Mercury are largely devoid of volatile elements". If that's the case, why does Venus have so much carbon dioxide?
(I'm not saying the article is wrong, just trying to understand.)
Venus doesn't have liquid water, which is needed for the reaction of silicates with CO2 ("weathering"). Without that reaction, CO2 just accumulates in the atmosphere. Most of the carbon on Earth (and there's a lot) is locked up in rocks.
There's also a biological effect. Here on Earth, silica in the ocean is scrubbed out by microorganisms that create silica shells; these tiny shells fall out into sediments, where (in deep ocean) they eventually form a kind of biogenic rock called "chert". Elsewhere, typically in shallow water, carbonate rocks are formed from the remains of other kinds of animals. Without these effects, the dissolved silicon concentration in seawater would be orders of magnitude higher, and the silica would react to form clays. This reaction would acidify the ocean and prevent carbonate formation.
Just such "reverse weathering" has been hypothesized to occur after the Permian-Triassic boundary, where CO2 levels stayed elevated for 5 million years. The extinction event was so severe it disrupted chert formation (a "chert gap").
Keep in mind that carbon dioxide is almost 3x heavier than methane. Part of the reason Venus has "so much" CO₂ is because all the lighter gasses have been depleted.
(But yes, Venus is hard to satisfactorily explain, regardless of whether you accept the article's conclusions at face value.)
Except Titan likely has more water on it than Earth. Therefore unless we’re a fluke of a solar system planetary bodies with water on them should be extremely common.
Titan is outside the frost line. There’s no question that there’s a huge amount of water in solar systems, the question is if there’s a consistent transport system (comets, in this case) that moves it inside the frost line to where liquid water can, given an atmosphere and gravity, exist in conditions that match our familiar conditions for life.
The article mentions that the inner planets were initially too hot to retain water, but presumably Titan didn’t have that problem, being much farther from the sun.
Titan is interesting, but much further away from the sun, so different conditions. We want earthlike conditions, life that can sustain on anything else, is just hypothesis so far.
Mars is further out in the solar system, and I'm assuming it was further out than Theia when the collision occurred.
The article doesn't say no planets can have water, but just that originally Earth was too close to the Sun to have liquid water. Theia, according to this hypothesis, was not.
In the scale of the universe this is bound to happen, likely infinite times anyway and this is what feels rather weird to me. Not just the perceived "special circumstances" but that independent of the rarity it will still happen many many times and then any conscious lifeform developing technology to realize this be subject to the definition of survivorship bias.
That's what is suggested here but according to the Giant Impact Hypothesis the impact happened about 4.5 billion years ago and formed the Moon from debris, and it likely vaporized much of any existing water on proto-Earth rather than delivering it...
More investigations needed ...
What I don’t understand is how you define a single point (even if the point spans a million years) of “when the solar system formed.” They say the chemical composition of the Earth solidified “only 3 million years after the solar system formed” — isn’t the formation of the planets itself part of the formation of the solar system? How does one define the moment of formation? Or does this mean that we know with certainty that there was no physically consistent body one could identify as “Earth” 3 million years prior, and then within those 3 million years, it coalesced and solidified?
I was under the vague impression that there is a single moment when the gravitational force in the core of the proto solar system outweighs (ha!) the electromagnetic repulsion of deuterium/tritium nuclei and fusion is achieved.
The resulting radiation pressure clears out the debris from the solar system’s accretion disk, and this process surely is not instantaneous but is relatively fast.
We don't. It's usually within a range. My illustrated book shows the timeline with more context and detail. Note that the events are provided on a timeline with some uncertainty (e.g., ± 1 million years):
What are the chances of the Earth forming yet remaining dry?
Exoplanet surveys that I've seen in popular press can see rocky, dry planets. I'm not sure if that's just a selection bias in our current technology or if Earth with ocean and atmosphere is relatively rare.
I don't understand why all these volatiles (hydrogen, nitrogen) didn't evaporate during such huge collision, which likely melt the whole Earth's crust. Even if a temporary atmosphere was formed, with high post-impact temperatures this atmosphere can't stay long.
As far as we know, molecules and atoms escaping into space comes due to the solar wind. Somehow the solar wind activates these atoms and carries them off into the distant vacuum, ad infinitum presumably though (I would imagine) limited by the heliopause.
[edit, benefiting from convo: mechanisms on atmospheric escape, to varying degrees of verification)
Absent that, our treasured atmospheric molecules would have to autonomousy achieve escape velocity, some 22 km/sec , with no outside assistance. A difficult feat. And so, resident atmosphere.
With high enough temperature some molecules may achieve velocities enough to escape. The question is - how hot was it really? The initial collision happened at least with escape velocity, so there was roughly enough energy for volatiles an non-volatiles to escape. But non-volatiles condensed presumably pretty quickly (but were still hot) in comparison to volatiles.
Yes I was being a bit too glib in relegating atmospheric escape mechanisms exclusively to action by the solar wind. Lot of proposed mechanisms, uncertain how many of them are verified and quantified to what magnitude.
As a layperson I see our current epistemological state as long on models, and short on empirical verification (because we're talking about a difficult phenomenon to verify).
I think I mostly wanted to offer counterpoint to the original comment that 'this atmosphere can't stay long' i.e. even under elevated temperatures.
(I'll probably update my prev comment with those wikipedia links.)
The water also helped with cooling the surface right? And I thought this was already a widely accepted theory, that the water came from a meteor or asteroid.
That is pretty much the premise of Hal Clement's short story "Halo", which I read in _Space Lash_ (originally published as _Small Changes_), but now available in:
I recommend folks read it in reverse chronological order, starting at the back, then working to the front and bailing when things get too quaint/old-school/golden-age.
It seems we only developed in the last 90% of time during which solar eclipses are possible. Perhaps we're slow compared to our galactic sisters and brothers.
Imagine the real twist being that complex intelligent life on a planet only goes past some critical development point if there's some sort of weird coincidence in the sky that pushes its inhabitants to understand the mystery.
It's the weirdest filter: you need a giant sign that points you where to look for answers. Without it, you're less likely to find what the universe is all about.
Well, I for the count of one, didn't think it bad, but thought provoking. We're all immigrants, when you get deep into it (speaking from Europe, where we usurped previously native folk some 1500 years ago), and we all came from Africa anyway.
But, yeah, political implications nowadays are a slippery slope.
Which is possible, at least from sites elsewhere in the young solar system. Life might have originated on Mars, for example, or perhaps in one of many small, warm, wet asteroids. These early asteroids were kept from freezing up by the presence of short lived radioisotopes, the decay products of which are detectable today in parts of meteorites.
The Earth has a nearly perfect circular orbit. Any collision with another planet would have pushed it off its orbit and caused it to at the very least created a more elliptical orbit that likely would have made the swings in temperature more deadly for life on Earth.
> The Earth has a nearly perfect circular orbit. Any collision with another planet would have pushed it off its orbit and caused it to at the very least created a more elliptical orbit that likely would have made the swings in temperature more deadly for life on Earth.
There is a lot of evidence of a big collision, but that's a very good question anyway!
I guess the interactions with other planets and asteroids change the orbit to a more circular one. I couldn't find a serious source that confirm, and not even a non-serious, so I'm still curious, very curious.
Anyway, there is a good theory that Jupiter formed at 3 AU and moved later to 5 AU and (very slowly) caused havoc in all the outer solar system https://en.wikipedia.org/wiki/Formation_and_evolution_of_the... So the initial orbits are not fixed in stone.
Furthermore, robotic exploration of Mars is already yielding sufficient evidence that Mars once had oceans. There is a well-founded suspicion that Europa and Titan have seas hidden beneath their surfaces. Does this article mean that all of this is just our imagination? I don't think so.
It's backwards. Highly eccentric orbits are the default; near-circular orbits are the inevitable result of averaging out a large number of orbits after they collide.
It's also ignoring the fact that we likely did have additional planets, but after interactions with other planets with nearby orbits, they would have been either ejected out of the solar system entirely, caused to collide, or herded into more circular (non-overlapping) orbits.
While I agree with you on most points, that is not why Pluto is not a planet.
The reason is that it was observed "too soon" because of its interaction with Neptune's orbit. Once we realized there were plenty of such objects in the range of Neptune's orbit but we also realized that these were not fully formed planets, we invented the term of dwarf planet, so Pluto was demoted to that status, which it shares with many other objects in the far out orbit.
So, it was just a classification thing. We could have also said all those others are also planets.
the fact is that there are over 700 quintillion planets in the universe, habitable is over 40 billion... i think our current understanding of physics limits our ability to reach any of them.
Reading comprehension: The collision with Theia likely had a large effect on Earth once it occurred, but the collision might still have been unlikely to occur in the first place.
We humans are not from Earth, what more signs need those who can't see?
Humans,from all the species, the unique without a natural habitat.
Humans, can not live on this planet unless we all get together and start adapting the environment. Otherwise, we can only survive and it's not fun.
We have to wear clothing, cut downn trees.
We get ill and stuff.
Monkey us from? We closer to the pigs and not just the hips.
Of course, yes -hell, even cats have their own AIDS; but what I meant was we get 'easily' ill. I mean, imagine we have to drink the water from a puddle?
Hey that bit was for the lols,
although it is quite valid to say, just missing plural and a comma.
Innacurate in some ways -mainstream theory is not about coming from apes, rather is about sharing a, yet undiscovered, common ancestor.
I mentionned the pigs because of promising advancement in organ transplantation, notably kidneys that reached a milesone recently, and I mentionned the hips because human hips and ape hips have an evolution-breaking distinction.
I could go on and on, but let's wait for more science, it wouldn't surprise me that what knowledge we discovered and took for granted back then, when 80% of the world population did not know how to read, might be developped today.
I really appreciate your open response! Your writing style is so fascinating, it reminds me of how my dad used to talk (he was Persian, not a native English speaker). What’s your background? How did you end up with these beliefs?
Thanks for the kind words. My heart is Belgian and I'm living in Panama now;
Well, I always wondered why we 'evolved to die', in the sense that from my understanding, the initial life forms, quasi-minerals, wouldn't die of old age, just of trauma like cell rutpture or something.
There is so much to say so I really cut it short, but eventually I read about how it was probable that first living things came from an asteroid, I started thinking that 'something', call it God if its meaning hasn't been perverted by manmade things, put us there. Something currently above our understanding, and quite extraordinary -what kind of energy to run the universe.
From a purely mathematical, scientific, and logical standpoint, I must regard this article as entirely speculative. The scientific claims it presents are extraordinarily improbable, and sound reasoning compels their complete dismissal.
History repeatedly shows that the popular: "extraordinary claims demand extraordinary evidence" is often dependent on the frame of reference.
What is thought to be likely is used to frame conventional wisdom as truth, making the new viewpoint "extraordinary, until, over and over again, the new viewpoint becomes conventional wisdom. So "extraordinarily improbable" is really just an overton window framing (what we accept/don't accept), rather than a statement based in logic. Though your overall framing reminds me so much of historical phrases that I wonder if you are being intentionally ironic.
The Big Question:
How did Earth become a planet with oceans and life, when it formed so close to the hot Sun?
What Scientists Did:
- They used a "radioactive clock" made from two elements: manganese and chromium
- Manganese-53 breaks down into chromium-53 over time (like ice melting at a steady rate)
- By measuring these elements in meteorites and Earth rocks, they figured out WHEN Earth's basic chemistry was locked in
Key Finding:
Earth's chemical recipe was set within just 3 million years after the Solar System formed (that's super fast in space terms!)
The Problem:
At that point, early Earth was missing the ingredients for life—especially water, carbon, and other "volatile elements" (stuff that evaporates easily when hot)
Why Earth Was Dry:
Close to the Sun, it was too hot for water and other volatile stuff to stick to the rocks that built Earth—they stayed as gas and floated away
The Solution:
About 70 million years later, another planet called Theia (which formed farther from the Sun where it was cooler) crashed into Earth:
This collision created our Moon
It also delivered water and other life-essential ingredients to Earth
The Big Takeaway:
Earth needed a cosmic accident to become livable. Without that lucky collision bringing water from the outer Solar System, we wouldn't be here!
Why This Matters:
If Earth needed such specific, lucky events to support life, habitable planets like ours might be much rarer in the universe than we thought.
This could mean in the Drake equation ne -number of planets capable of life- is very small. A planet has to be hit with a comet big enough to deliver a large amount of water but not so big or fast to destroy it. And be in the Goldilocks zone of the star. Also the mass of the planet would play a part - gravity of more massive ones would be more likely to capture a comet. But again, too massive and I could see that hampering life.
The Drake Equation is filled with assumptions, like life must appear on a planet in the Goldilocks zone of a star. The whole equation has only one datapoint to extrapolate from. Tweak the equation's parameters and it will predict universes that only have one civilization per galaxy or worse! We have no way of knowing what those parameters are because we haven't seen other examples.
A major reason we are interested in Europa is because it might have underground oceans. Hypothetically, through tidal forces with Jupiter, the moon's core is hot enough to create oceans under the ice crust. Combined with hydrothermal vents you have the possibility for deep sea life similar to our own deep oceans. The Drake Equation does not predict this possibility.
The Goldilocks zone doesn't enter the Drake equation at all.
As a reminder, this is the equation: https://en.wikipedia.org/wiki/Drake_equation#Equation
It makes very few assumptions.
The equation itself makes no assumptions. But anyone trying to calculate something with it must.
The last five factors in the equation will be filled in by assumptions based entirely on one data point, life on Earth. From your link:
Can you define any one of those without assumptions, in a scientifically proven way?One approach is to give each variable a probability distribution. The greater our uncertainty about possible values, the wider the bell curve.
Drexler and colleagues did that, and found "a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively). ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable."
https://arxiv.org/abs/1806.02404
A probability distribution describes how likely different outcomes are. It requires multiple observations or an assumed model that can represent variability.
Likely are also making a probabilistic independence assumption.
Probability distributions based on a single data point (of where we know there is life) aren’t reliable distributions.
Which is why they set very wide ranges on the things we know little about. Doing that is less unjustified than guessing specific values, as people have usually done.
It's nowhere near a precise estimate of the probability of life. What it mainly shows is that the Fermi "paradox" is no such thing. It can look that way if we guess specific parameter values, but if we fully account for our uncertainty on the various parameters, then the result is a decent chance that we are alone, given the knowledge we have so far.
I’m not saying precise. I’m saying it isn’t even an estimate.
You can’t have a distribution with one data point.
It’s similar to the arguments about 3I/Atlas being an alien spacecraft because it’s so ‘weird’.
With so few data points, everything is fundamentally ‘weird’ - or normal - we have no way to tell, so making any sort of statistical argument about it is fundamentally useless and misleading, as statistics is based on groups. And we don’t have a group yet.
We know a lot more than the simple fact that civilization exists on our planet. See section 3 for how they estimated the parameters.
One of the most uncertain parameters is the rate of abiogenesis events per planet. For that one they used a log-normal with a standard deviation of 50 orders of magnitude. They discuss specific theoretical limits from biology for both ends of the range.
Compared to this approach, the usual method is to just pick particular values out of a hat. This paper at least improves that by directly representing our vast uncertainty for some of the values.
It doesn't tell us how many alien civilizations there are. But it does tell us the range of possibilities, given what we know and don't know.
Except we don’t actually know the real ranges of values here, so our actual level of uncertainty is still infinite.
If your level of uncertainty is infinite then you're suggesting that abiogenesis could be happening every day in your back yard. I think you might admit we're a little more certain than that.
Really?
Life, once established, is about competition for niche resources. Established life would kick the polypeptides out of a protocell quite easily (with certainty > 99%).
Protocells could be evolving right now at vents in the ocean, with zero of them managing to escape their birthplace due to being outcompeted by things with fully developed organelles.
In the same sense that we could be certain that life never generated and we’re in a simulation, sure.
No, it’s just a starting point. We do need more data.
It actually adds excessive structure.
The underlying model is just:
N*f
How many planets are there, and what proportion of them have detectable life?
The f does not have to be structured as fl->fi->fc, although we can see why you'd assume that kind of structure. It's simple to calculate the PI(series) when the model is just a funnel. Like the Million Dollar Money Drop gameshow.
But you could imagine a more complex model of probabilities that branches and merges. There could be events on the bayesian tree that amplify downstream events. For instance, suppose there is some pathway that if reached will leave certain minerals that future civilizations could use. This has happened already on earth at least once: lignin bearing plants could not be easily digested for a long time, and that led to coal formation during the carboniferous period.
You could imagine many such potential trees, but we only have one iteration.
It does assume that life must be associatable with a planet. It's a plausible assumption, but you could also hypothetically have life develop on a star itself or its remnants, comets, clouds of interstellar gas. Maybe even something more exotic than that (dark matter? some weird correlated statistical properties of the quantum foam?)
About forty years ago I read a terrific book about life forms that live on a star. Maybe Starquake was it called? Did to the abundance of energy on the surface of a star, they live their lives a million times faster than humans. Thus for both them and the humans who discover them, communication is difficult. I think the humans push these life forms to develop civilization, which from the human's perspective had them go from primitive animals into sophisticated beings of technology past their own in something like a day.
That's "Dragon's Egg" by Robert L. Forward, a classic Sci-fi story:
https://annas-archive.org/md5/4c381ac344506d10037fc8e7747098...
The cheela lived on the surface of a neutron star, and they lived faster because the nuclear physics that powered their metabolism are far faster than the chemical and mechanical physics that power our own.
And "The World at the End of Time" by Frederik Pohl.
https://en.wikipedia.org/wiki/The_World_at_the_End_of_Time
There's also Sundiver by David Brin, which has plasma life forms in our sun.
I'm not against piracy, and I love Anna's Archive... but publicly linking directly to a pirate source for something like this seems wrong. Could've just linked the Wikipedia page and let people acquire however they prefer.
Anyway, sounds interesting, gunna add that to my list
It's 45 years old and the author is deceased. I assume you would be untroubled by a link to a copy of Macbeth. Where do you draw the line?
Well I don't really have a line, but that doesn't mean I'm going to go linking directly to such sources in public - not everyone agrees with my stance on copyright. Those who do can easily go find it themselves.
Also Macbeth was written 400 years ago. Let's not pretend this is a fair comparison. This author has been dead only 20 years - it might be that their partner is still alive and needs that money, or their children.
Why won't anyone think of the publishers and the book stores!
Amazon is hanging on by a thread, and piracy is stealing their cut.
An obvious line would be when copyright expires. In fact, drawing that line is exactly what copyright expiry is intended to do.
Copyright has far exceeded sane limits a long time ago.
What's a "sane" point at which you become entitled to other people's work?
What a strange way to phrase it, considering in your last comment you were talking about how copyright expiry is exactly for this purpose.
Anyway, what is copyright expiration in America these days? 100 years?
Also, is it simply a matter of X years after creation? I somehow doubt it's that simple anymore. I wouldn't be surprised if "copyright is extended indefinitely if the work is being actively commercially used" or some such
Patents are for 15-20 years.
Which is saner eh! That way people living at the time who are protecting it (copyright and patents are both protections for things otherwise being distributed and which could be copied easily) can benefit from it eventually.
100 years is just rent extraction.
My initial reaction was the same, then I thought: "no, we need more of this".
We need more discussion about copyright in our society, and we need it most in front of those who are unaware, inattentive, or would otherwise shirk that discussion. Posting a relevant link in a relevant discussion appears as good an avenue as any to get people talking.
Promoting copyright infringement in order to initiate a conversation about copyright is about as moral as murdering civilians to initiate a conversation about human rights.
Is that really the equivalence you want to make?
That's a rather severe escalation to me.
This... isn't a discussion about copyright though?
It wasn't, until https://news.ycombinator.com/item?id=45477785
That is about piracy, not copyright.
I cannot make sense of that statement. Other than in relation to copyright, I don't see any relevant discussion here about piracy.
Yes, that was it!
Andy Weir’s Project Hail Mary had an interesting take on that.
I was bothered by the nearly a-scientific-ness of PHM. The story was nicely done in general, but it feels like he pretends to be hard science fiction when he's really Star Trek-level.
Those variables come with embedded assumptions they are essential and meaningful to discovery of life and civilization elsewhere in the universe.
For all we know civilization exists inside our car battery. Why assume it only exists on planets.
It's not explicit in it's assumption but implicit assumption the equation is meaningful.
>For all we know civilization exists inside our car battery.
Rick Sanchez uses a microverse battery
Thanks, I read that part before I shared it. It's pretty clear to me, these are pretty well defined quantities, just hard to measure. What is unclear is perhaps the definition of life. But at no point does it assume a planet must be in the Goldilocks zone. So perhaps you want to point out those assumptions you are talking about to me, because I don't see them.
Edit: the parent post has been edited substantially after I replied.
> these are pretty well defined quantities, just hard to measure.
They are "defined" conceptually, in words, not in physical quantities. It assumes we can assign a known value to any of that when we don't and likely never will. It's like saying "Let X answer the unanswerable question. X is the answer".
> at no point does it assume a planet must be in the Goldilocks zone
You could say it implies it with fl.
> Edit: the parent post has been edited substantially after I replied.
Only for legibility.
How can you extrapolate those terms from a single planet with known life without making assumptions?
I can't, but the equation itself doesn't to that. The assumptions are up to the reader to make. That's why I think that the equation isn't particularly useful.
I'm assuming they were referring to this term:
> n_e = the average number of planets that can potentially support life per star that has planets.
The fact that the planet is neither too hot nor too cold would seem to be a major component of this term:
https://en.wikipedia.org/wiki/Habitable_zone
That's just your interpretation. Take the equation at its face value and it does allow for life originating around some deep sea vents, like JamesLeonis speculated.
It does seem unlikely that such life forms would ever become spacefaring.
That's a separate term in the equation.
Yes, but we should consider these linkages when setting values. If we assume that volcanic vent life is very unlikely to become spacefaring, we should either leave it out of the "life" term, or leave it in but lower the probability of the "becomes spacefaring" term.
yeah you are right the Drake equation does not assume Goldilocks zone.
It goes the other way around. The Goldilocks zone is a shorthand attempt at helping us guess how many planets out there are capable of supporting life.
The biggest assumption is that it assumes only a single path to intelligent life.
Even if you only had a handful of civilizations, the sheer time that has passed and size of the universe should mean that life should still be alot more apparent.
With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
Another point I feel is that proliferation of life should be an self-reinforcing affair, for intelligent life even more so. A spacefaring nation may terraform or just seed planets, and these in time will replicate similar behaviors. At a certain point, a galaxy teeming with life should be very hard to reverse given all the activity. A life itself isn't necessarily evolved from biology, AI machine lifeforms should also well suited to proliferate, yet we don't see them anyways.
At some point replicative drift will set in. How many replications is two million years? How long before the probes evolve? How long before they speciate? How long before a species turns on itself?
> Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
Time, not space, is your answer here.
Two reasons -
(1) civilizations might not survive long enough to do this.
(2) 13 billion years is a long time. So you have the reciprocal of that as the chances to be in the right year to see such a probe. And with results from the new telescope we now have hints that the 13 billion number is bogus, the universe is likely far older.
> With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere?
What are the incentives to build and deploy such a thing though? We as a civilization fail to fund things that have a ROI of more than a few years, how are you going to fund something that pays off after a million year?
Exactly. Some of the biggest explanatory factors for the Fermi paradox are likely to be economics and politics: interstellar travel is unreasonably expensive, unimaginably slow, and has negative ROI unless your time horizons are beyond anything that's ever been used on Earth.
Consider that in some countries on Earth, we can't even get consensus that obtaining energy directly from the Sun via solar panels is a good idea.
Also, people vastly underestimate how hostile space is: colonizing Mount Everest, the Antarctic or the continental plateau under sea would be far easier than colonizing Mars. And Mars is the most hospitable extraterrestrial place we know of.
I don't think we would colonizing Mars, free floating colonies akin to O'Neil Cylinders orbiting Earth would probably be the more logical option. And with increasing robotic automation capabilities, it's not improbable to see these being built in the future.
> it's not improbable
"Extremely improbable" would be a better assessment.
Even ignoring the project complexity, difficulty, and energy budget, which can't simply be handwaved away by "robotic automation", one reason is simply that such colonies don't solve any problem that we're likely to have, that can't be solved much more cheaply, safely, and effectively.
But even the idea that we'll eventually have the technology to build such structures is debatable. Will this be before or after we solve climate change, for example? Because that issue is likely to severely impact our technological capabilities over the timescales involved. And as of today, the most technologically advanced nation is doubling down on atmospheric carbon production.
Having the technology to build it isn't the hard part. The question is why you'd do that in the first place and who would fund such a colony.
First of all it's going to be massively more expensive than any housing we've ever built on earth so only a very small elite could afford living there.
But then again, space is a very hostile environment: it's super dangerous (any incident will almost certainly snowball into a dramatic accident), very unhealthy (billionaires are currently funding longevity research, so I don't think they'd like to go in a place where they would age up significantly faster than on earth…), and life is just worse up there on all respect…
FYI just about every outer solar system moon or planetoid has a liquid ocean somewhere underneath. Europa is neither exceptional or even that interesting anymore.
Yup
The fundamental problem with the Drake equation is that it's frequentist, not Bayesian
Hence why you get too high sensitivity to parameters you have no way of having an estimate with a small margin of error
We "don't care" about how many civilisations are out there, we care to the point where we can interact with them.
As mentioned, it has several assumptions. "Rate of birth of sun like stars" means nothing. You can "always" have an exception for life that will throw the data off: "star too bright but with a hot Jupiter tidally locked in front of your moon, shielding it" etc
> star too bright but with a hot Jupiter tidally locked in front of your moon, shielding it
It seems unlikely that such exceptions would amount to more than part of a reasonable margin of error.
It is very likely that Earth itself is the exception of the exception and is part of a "margin of error"
Not really there’s always gonna be water comets in the frost zone.
I don't see any reason to believe that giant impact is the only way to get life-supporting amounts of water. We know Mars had liquid water. We know Titan has lots of ice. We're pretty sure Venus at least had noticeable amounts of water. Did all of these come from Theia-type impacts? I don't think we have any evidence of that.
Multiple impacts is the standard hypothesis for a source of Earth's water. If I recall correctly, outgassing from volcanos is another source.
Keep in mind, the solar system formed from a relatively homogenous nebula. It was the formation of the sun that forced lighter elements to migrate outwards, and that only happens if the lighter elements aren't already part of a larger object. There isn't much of a difference between a 10 km chunk of ice and a 10 km chunk of iron gravitationally speaking. Bouancy doesn't play a role here, so density doesn't matter. Outgassing does matter, but that is a slow process for large object, like the Earth, or for smaller objects on Earth crossing orbits that don't get too close to the sun.
It's also worth considering that each planet's situation is unique. There is much more water ice on the moons of the outer solar system because there was more water at the time of formation and the lower temperatures mean the water that was there stayed there. As for Mars, even though it is colder than the Earth, it is much less massive. As such, its atmosphere bleeds away lighter molecules (never mind lighter elements).
> Multiple impacts is the standard hypothesis for a source of Earth's water.
Right, which is why it's baffling to me that everyone in this thread seems to be losing their mind over this result, thinking it affects the Drake equation and rewrites solar system dynamics. The multiple impacts thing might not have actually happened to earth, but there's still no reason to believe it wouldn't work.
Yep, mega-impact is a classic example of an ad-hoc hypothesis. For example, Moon formation is much better explained by multi-impact hypothesis, which also requires less assumptions.
Dang, I can't post anything in this thread without someone thinking I agree with them that science is BS. Giant impacts aren't actually surprising in an early solar system that hasn't hit steady state yet. If multiple impacts better explain all the evidence for Theia, including the weird patterns of isotopes and possible fragments deep in the mantle, that's news to me.
I recently became addicted to the SpaceSimsx and SimulaVerse. My takeaway is that so many just slight deviations can extinguish life on earth. I used to think of possibility of life in other worlds just in the lens of statistics. There are so many combinations and possibilities that it seems inevitable. But seeing just how perfectly aligned our solar system is makes me really reduce the probable number of chances of other habitable scenarios in my mind.
These channels helped me realize just how important all the planets in the solar system are to our continued existence. Its as if we have an entire family thats just perfect to make our existence possible. An entire family each one quietly doing their part without fanfare or credit.
What if we had 2 moons with half the mass?: Destruction [0]: https://www.youtube.com/shorts/v3xxaTkKGTQ
What if we moved Earth 5% further from the Sun?: Destruction [1]: https://www.youtube.com/shorts/g-na5x0Kldk
What if we dimmed the Sun by 1%: Destruction [2]: https://www.youtube.com/shorts/Cc3DRRJxhB8
What If We Delete the Biggest Planet from Our Solar System?: Destruction [3]: https://www.youtube.com/watch?v=kHJpIWoksKw
What If We Delete All Gas Giants Except Jupiter?: You guessed it...Destruction [4]: https://www.youtube.com/watch?v=Eg9fPNg00EE
> perfectly aligned
No matter what the circumstances, live will evolve to perfectly match the conditions it is under. There are many species so perfectly adapted to their ecological niche, they are in great danger of extinction. Like peacocks, who are stuck in a local optimum with no way out.
Well, just keep in mind that its not a "perfect alignment" as this seems to prescribe some kind of intent. It's more a set of requirements that allowed life to not be extinguished so easily. We could never exist in a place where this didn't happen like this, so obviously we have to be here and not some place ealse. So its more that out of the 1 places we have seen that was made like this, we at least know life happened there.
Could a tardigrade withstand these scenarios? If the answer to any of those is yes, could we then say that even with the parameters skewed a bit, there is a chance life exists elsewhere, and under completely different and extreme or (not "normal") conditions? Is the tardigrade here as a "clue" to tell us that life could form potentially anywhere?
The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time.
e.g. Say chance of a random planet ever being hit by a water-carrying comet is one in a billion, then with 100B - 1T planets in the milky way it'd happen here 100-1000 times. If chances are only one in a trillion, and we're the one in the milky way, then there are still another 100B - 1T galaxies out there and therefore a similar number of such events.
> The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time.
But numbers can go arbitrarily low.
And you have to have multiple low probability events. These probabilities multiply.
We had a good start. A Jupiter to clear the debris, a Theia impact to create tides and contribute to tectonics, a magnetic core, a shielded atmosphere. We had water delivered to us. Maybe even panspermia.
Maybe cell walls and mitochondria are hard. Maybe multicellular is hard. Maybe life on land is hard. Building lungs, rebuilding eyes, having actual energetic gasses on land...
Maybe life is easy, but intelligence is hard. Maybe civilization is hard.
Maybe technology development can only happen on dry land, because aqueous chemistry is hard in water. Sorry mollusks and cetaceans: you'll probably never be able to do chemistry or materials science.
Maybe you need water and carbon and other chemistries aren't robust enough.
Maybe you need lots of fossil fuel deposits to develop industry. And that requires growth without bacteria and decomposers for millions of years, implying a certain order to evolution.
Maybe you need a certain sized gravity well to escape.
Maybe surviving the great filter is hard and still ahead of us. Maybe every species can build tech where a kid in their garage can extinct the entire species by 3d printing grey goo.
There's just so much we don't know about how life could happen. Let alone intelligent life. We don't even know where we're headed.
> Maybe life is easy, but intelligence is hard
Intelligence has evolved three times independently on earth - dinosaurs/birds (raptors, covids), mammals, and cephalopods (Octopus)
> Maybe you need water and carbon
Maybe so, but Oxygen and Carbon are only behind (albeit far behind) Hydrogen and Helium as the most abundant elements in the universe
My pessimistic side says that the conditions for intelligent life are so implausible that we’re unique, and when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
Basically I fear we’re the universe’s only shot of appreciating and populating the galaxy (or beyond) and we’re on the brink of throwing that away.
> when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
There will be no successor civilization to humans. Earth won't be able to support multicellular life in a few hundred million years due to the sun becoming gradually more luminous over time, resulting in higher surface temperatures that will eventually culminate in a runaway greenhouse happening, as it already has on Venus. Due to human-driven climate change effects this event will certainly happen much sooner (<100m years) as well, which is simply not enough time for another intelligent species to evolve after a large-scale extinction event.
Even if life evolving on earth was an incredibly rare event the chance of such circumstances not happening elsewhere even in our own galaxy is infinitely small - there are trillions of planets and 100b+ stars. On top of that there are 100s of billions of galaxies within the observable universe as well.
> Due to human-driven climate change effects this event will certainly happen much sooner (<100m years) as well
No, it will not. Human driven climate change is drastic, but the Earth has seen far worse events than our anthropogenic carbon emissions. For instance, the Chicxulub impactor at the end of the Cretaceous changed atmospheric conditions overnight, and to a much greater degree than whatever we have cooked up. It was the equivalent of detonating the world's entire nuclear arsenal about a million times over.
Sure, it finished off the dinosaurs. But 66 million years later, we, the descendants of tiny rodent-like mammals, are still here, as are the dinosaur's own descendants, the birds.
Additionally, during the Carboniferous about 300 Mya, both carbon dioxide and oxygen levels were considerably higher than they are today, and life actually thrived. I would say that with the increasing luminosity, there will be at least a decent period on Earth where life returns to that sort of diversity. We are actually still only in an interglacial of an ice age—this has effectively sterilised large tracts of our planet by covering them with ice sheets, or locking permafrost into the soil and making them unavailable for large trees.
Let me be very clear: our emissions—if unchecked—will make life very difficult for us as the rising seas and temperatures scatter millions of people out of coastal cities in the tropics further north and south and cause war, division, strife, and discord like we have never yet seen. But actually bring forward the planet's overall demise? Nearly impossible.
Let's not have the hubris to think we puny humans could remotely affect the planet's geological timeline. If we somehow all disappear simultaneously, most direct evidence that we ever lived will disappear with us–perhaps within a hundred thousand to a million years of erosion and weathering. Our emissions will similarly lurch to a halt and will reach equilibrium within a similar time span. That's all it takes to remove our direct creations from the geological record.
> There will be no successor civilization to humans. Earth won't be able to support multicellular life in a few hundred million years due to the sun becoming gradually more luminous over time
Modern humans have only been around for < 1 millions years, and all the technology we have invented is incredibly recent. 200 years ago we had neither electric light or bicycles.
Over the course of 100s of millions of years, as the sun's increasing luminosity becomes an issue, I'd have to assume we could create some sort of atmospheric solar shield to reflect or absorb a lot of the energy. Of course you can only postpone the inevitable (red giant).
Assuming the evolutionary lineage of our species survives a few hundred more million years (which seems rather doubtful), then it's not going to be homo sapiens any more - we'll have evolved into successor species that may be barely recognizable. If you go BACK in time 100M years, our ancestor was some mouse-like animal.
As long as we have air and water (i.e. as long as we're alive), then we can make propellants such as Methane or Liquid Hydrogen and LOX, Hydrazine & Dinitrogen Tetroxide (or Hydrogen Peroxide).
None of which are, I assume, as easy/efficient/effective to integrate into a new civilization's tech tree as coal & oil.
So? We build nuclear power plants and it's not exactly easy/efficient to extract uranium. Hard things are done all the time.
Having coal/oil is pretty irrelevant in terms of whether a civilization can build spacecraft.
"and when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet."
Successor. Whoever comes along after we've done ourselves in.
Huh? "We" is the human race, whatever civilization. What point are you trying to make? What I said stands, exactly how I said it.
What has that got to do with energy dense rocket fuels for getting to orbit ?!
The key phrase was "successor civilization".
> ...when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.
On the flip side, that could also be plausibly a blessing, avoiding them to fall into the same trap of becoming too powerful before they get wise. These comics illustrate it: https://www.badspacecomics.com/post/grounded
Even on Earth, the only reason humans exist is because the “local maximum” of the dinosaurs was wiped out by a meteor. Perhaps comparably intelligent dinosaurs would have eventually evolved - but it’s not a given!
Dinosaurs existed for some 200 million years with no detectable signs of technology development[0]. Presumably, the steady state did not produce a scenario in which the intelligence niche would develop without some other less catastrophic global change event.
[0] Unless that episode of Voyager was right on the mark https://memory-alpha.fandom.com/wiki/Distant_Origin_(episode...
Intelligence evolved at least three times on earth - dinosaurs (leading to corvids, but a raptors already intelligent), mammals and cephalopods (e.g. octopus).
I suspect that any evolutionary environment will eventually create enough variety and instability that some generalists emerge, creating a reward for intelligence. The rise in intelligence from early water-bound life to later forms was likely all driven by more complex and diverse environments.
Maybe they didn't produce an intelligent species just because they had not the luck of living in the unprecended time in the history of Earth with both high atmospheric O2 and very low atmospheric CO2 we enjoyed for a while, before we started to burn fossil fuels by the gigaton. See https://www.qeios.com/read/IKNUZU
It took several environment-changing events to get our unique kind of intelligence; mammals had to thrive in place of saurs; and then, Africa needed to be split by the Rift and to create the dry savannah.
This forced some apes to climb down the trees and depend on a diet of scavenging for meat, which happened to both increase brain size AND require improved intellect to survive, forcing the evolution of our hypertrophied symbolic brain.
Had this not happened however, other intelligent species could have filled the niche. There's no shortage of other intelligent species in our planet, not just other mammals but octopus and some birds. And then you get hive intelligence, which could equally be forced to evolve into a high problem-solving organism.
You're not wrong, but you're in the wrong place to talk to people about low-probability events and how they multiply. Most Hacker News can't into elementary-school-level probability equations and will instead take the ostrich approach; there was some behavioral scientist dude from Cambridge Analytica who wrote about this and the TL;DR is that most "adults" have infantile minds that prefer various safety blanket mechanisms that society is more than ready to offer them just to do anything to have an excuse to not face the truth of what basic math reveals to more likely than not be true.
> But numbers can go arbitrarily low.
Which begs the question, why 1, and not zero? I can buy zero, or a very large number. But 1 exactly? Nature doesn’t do that.
There’s not a huge difference between zero and one, other than whether someone’s around to comment about it on HN. And even a second wouldn’t really tell us more about the probabilities.
Siméon Denis Poisson would like a word with you.
But in seriousness, I agree.
Just as easily as we can multiply planets times systems times galaxies times cluster groups we can multiply multiple small probabilities of each chemical being present at the right time and right type, temperature ranges, gravity ranges, etc
If the numbers you propose turn out to be accurate then the odds of there being other life are near zero because even 1/1000 planets are not habitable likely.
Huh? Even in the 1-in-a-trillion case, there's still maybe 1 trillion galaxies each with one planet that was struck by a water bearing comet, so even if only 1/1000 of those are otherwise habitable, that still leaves a billion habitable planets in the universe with water.
I doubt water (H2O) is actually that rare. The most common elements by far, both in our own galaxy and the universe as a whole, are Hydrogen and Helium, but the next two most common are Oxygen and Carbon.
Do other galaxies matter here? A civilization would need to be incredibly powerful to be detectable from another galaxy.
At the moment, rapid and massive expansion seems likely with tech only just on the horizon.
Enough AI and robotics for an autonomous factory may be a mirage (such mirages have (metaphorically) happened before), but it seems like it's on the horizon.
Even with relatively mundane growth assumptions, that can go from "species inventing writing" to "Dyson sphere completed, is now sending out seeds to every accessible galaxy" on significantly less than the timescale of light crossing a spiral galaxy's disk.
Cmon the number of hypothetical extrapolations based on no data in these statements is beyond superstition to something like delusion
I think its the fact that if we really wanted to, we could probably make it happen already today. On a scale of a couple hundred million years, its possible we could reach most of our own galaxy, which is a small slice of time in the life span of the Milky Way. So the question remains, why hasn't this already happened, or has it?
If I put citations into everything I write, I'd be a Wikipedia article, and people would still criticise the conclusions without reading any of them.
But contrawise, I do have data, they're broadly categorised as "history", "biology", and "all the stuff cited by Stuart Armstrong that time".
Galactic colonization, carried to saturation, would detectably modify the appearance of a galaxy. So called "type 3 civilizations" would convert a significant fraction of starlight to lower grade heat, which would be radiated. Searches have been conducted for this signature, with the result that no more than 1 in 100,000 galaxies has such a civilization, and with the result being consistent with none.
This is interesting speculation, but it adds one more completely unknown variable to the Drake equation.
What’s the probability that a radio-capable civilization becomes a galactic type 3 one? Looking at the only example we have, it appears very unlikely. It seems much more probable that we’ll destroy ourselves within the next centuries.
I am not an astrophysicist but I have a hunch any speculations of galactic colonization fails to entertain just how big space actually is. I feel like there is ample reason to suspect the probability of galactic (or even interstellar) colonization is exactly 0, and no civilization in the history of the entire universe will ever colonize an entire galaxy (and probably not even more than a handful of solar systems outside their home world; if any).
Your argument shows a lack of understanding of exponential growth.
Any given colony has to create only slightly more than 1 additional colony in order to drive exponential growth. There doesn't have to be any coordinated action by a central authority for it to happen. For it not to happen (if it is physically feasible), in contrast, every species has to refrain from doing it at all points in their history, almost without exception. And those that do the colonization will seed additional colonies with a mindset that led to colonization; such mindsets will be selected for for further expansion.
Permanent exponential growth is very rare in nature, and even rarer in biological systems. What we observe as exponential growth is usually only a partial observation of a logistical curve or is missing a system collapse at the end of the curve.
We have no reason to believe alien (or even human) civilization will continue to grow and expand forever. Heck even the human population curve has started to slow down and is now revealing it self to be a logistical curve.
But regardless of this, space is very very very big. And there are a lot of extremely hostile worlds out there. Any civilization will experience biological limitation to which worlds they can (and will want to) colonize. Likewise they will experience both economical and physical limitations to how far they will send their machines. Lets say an alien species is lucky and has a habitable world inside their solar system which they will colonize. I think this is likely. They also spot another world in a nearby solar system which takes them 200 years to travel to, eager colonists travel in a generational ship, and 600 years later the colony is thriving. Now they run out of nearby habitable worlds. There is a world of questionable quality 500 years away and they are unable to persuade enough people to fill a generational ship. Also they learned the stories of the passengers in the generational ship, their lives kind of sucked, we have it much better on this world. So it is better to just stay here. This might happen after 1 or 100 successful colonizations, but I think space is so freaking large, it will happen to all civilizations. At some point they will run out of worlds to colonize, and they will never expand far outside of some local area near their home world.
Unless some means of communicating faster than light is found a galactic colonisations is not a civilisation, its multiple ones. A colony ship heading in one direction at 0.1c will never interact with one heading the other way at the same speed. After 10,000 years the civilisations will be very different, after 100,000 years they will barely be the same species.
Even if 99% stop and fail, the 1% will continue and continue expanding.
The only way to stop would be to run out of planets, which would mean every habitable planet and star system has been populated. There wouldn’t be a biological urge to stop, as the successful colonies are ones which have the urge to expand. An environmental need wouldn’t affect every colony and ship short of a galaxy spanning event of some sort which we can’t even conceive.
Yes, I think that will never happen. My prediction is that generational ships are super rare in the universe, and may only happen ones or twice in the entire history of a civilization, and for a tiny portion of civilizations. Meaning by far majority of all civilization will have zero generational ships. Maybe a single civilization somewhere in a distant galaxy will have hundreds, but nowhere near enough to cover an entire galaxy, not even if we count decedent civilizations.
I also think fast space travel (like 0.1c) is rare among civilizations, and may only happen in the order of hundreds of time in the history of some civilizations. And most of these fast space travel will scientific instruments for curiosity and exploration, not for colonization. And that a technologically advanced civilization would favor doing their explorations with telescopes, not probes. So probes would only be sent long distance for rare occasions.
This would mean that almost no civilizations will be expand beyond their solar system, and those that do, will only do it a handful of times, and the expansion will finally stop.
It doesn’t matter how rare it is to get started once it starts. Every ship is a new civilisation that is created, one predisposed culturally and perhaps genetically to spreading out.
Especially once you reach the “hundreds” level then given the technology exists and the people exist why would it stop, until there’s nowhere else to go.
There is the light cage issue where a civilisation can only spread so far with exponential growth before internal pressures overwhelm it (the leading edge never gets a chance to continue as it is overwhelmed by trailing edges)
Even in that situation though you’d still have self replicating probes - likely at a far lower tech level than biological. Once you reach the tech to send one probe which can duplicate itself more than once using resources in a new system then its game over.
Send 50 probes to each of the 50 stars within 15 light years at 0.01c. If 10% make it they then use local materials and send 50 more, that’s 250 out in 1500 years. Then it’s 1250 out in 3000 years. Within a few millennia years you’ve got millions of probes spreading in an unstoppable way. The ones heading back “inwards” will fail, but those heading outwards will reach each new star dozens of times, only one will need to get there. Within 10 million years you’ve reached the entire galaxy.
To stop it you’d have to make a self replicating probe which was faster and did exactly the same thing and caught the earlier probe, but then when would that probe itself stop, it would have no way of knowing if there were any other “bad” probes to find without becoming the bad probe itself.
Living beings are the same. Once a few dozen have made it and passed on, it’s inevitable it will continue. It may leave out a hollowed husk in the origin point with all resources having being consumed in the centre, but that doesn’t matter as the centre has no way of affecting what happens on the edge, and one edge has no way of affecting another edge.
von Neumann probes are a fantasy. I see no reason why any civilization in the entire universe will ever build a successful self replicating probes, let alone ones that are still replicating dozens of millennia later. The reasons include that targeted probes and telescopes can give you pretty much the same amount of knowledge for far cheaper and much quicker then random walking probes across the galaxy. There is also a technical limitation to self replicating probes, even if a civilization will build one, we cannot expect the self-replicating mechanism to last dozens of millennia. Some generations will fail to replicate, and in the vastness of space that may mean the entire lineage will go extinct.
I think you may be expecting an exponential growth when population dynamics almost always favor logistical growth. At some point your machines, or your colonial behavior hits a limit and your growth starts to slow down. I suspect that limit is within the solar system for the vast vast vast majority of civilization. And even if one escapes their own solar system and starts anew on a new home world, they most likely will not colonize another. The space is just so big, and habitable worlds so far away from each other that I find it extremely improbable that any civilization (and their ancestor civilization) will survive more than 5-6 colonization (by far most will see 0).
> Living beings are the same.
They are not. You are describing living beings like viruses (fair enough; viruses are worthy to be considered lifeforms) that spread from host to host until they infect everybody. But viruses don‘t behave like that. The vast majority of them only infect their closest neighbors, and those that do spread towards the limit of all members of the species (like Covid) still fall short and eventually start to slow down their spread in a logistical manner. Growth only looks exponential while you are at the initial stages of spread. This behavior is not only common among viruses, but in fact most population dynamics can be described with logistical growth.
> von Neumann probes are a fantasy.
Well pack it up folks, we've been told what would be possible for any alien civilization, even given millions of years of effort.
Yes, theorizing a future possibility that has no president is, by definition, fantasy. I mean, you can do fantasy, it makes good science fiction, but until we have evidence that von Neumann probes exist and are capable of colonizing the entire galaxy, it remains fantasy. Theoretically we could build a high speed rail between Seattle and LA, we could build a permanent settlement on Antarctica, and we could replace our jet-planes with hydrogen powered flying wings, but until we do, a world with those things are just fantasy.
The only argument for von Neumann probes that I can think of is as a specific answer to the Fermi paradox. The universe should be filled with these probes, but since it obviously isn’t, we can infer that no civilization has reach the interstellar age.
I reject this framing, the Fermi paradox is only a paradox if you assume that space colonization is a thing that is not just possible, but inevitable. My solution to the Fermi paradox simply rejects this assumption. Civilization will not colonize definitely, they will do their space explorations with telescopes and targeted probes, and they won‘t build any von Neumann probes (at least not ones continue to replicate for dozens millennia).
Aside: I am aware of the irony that my description of civilizations outside of our solar system is also a fantasy.
It's rare in biological systems because it's terminated by running out of some resource.
But you're saying galactic colonization would terminate without running out of new systems to colonize.
There would be a slowdown due to geometric constraints -- only so many new systems adjacent the boundary of the colonized zone -- but that hardly solves your problem.
My speculation is that the size of space is an obvious geometric constraint which will limit the span of any civilizations almost immediately.
If we look at humans, we have both the space, technology, and the resources to expand even further on earth, yet our span only marginally larger then it was 10 000 years ago. We can have permanent settlements on Antarctica, floating on the ocean, etc. but we don’t. We can increase our population by another order of magnitude, but again, it looks like we won’t. This follows the same population dynamics as most other species on earth. I think aliens will be no different.
I guess it depends what question are we trying to ask. It may well be that there is no other intelligent life close enough to us, or coexisting with us in time, that we will ever be aware of it, but yet the universe may still be teeming with intelligent life.
In either case it's a statistical question of how common is life, and intelligent life, but of course there's the human interest in potential contact with another intelligent life form.
Unless collisions like the article suggests are a statistical inevitability, that is.
Hydrogen is the most common element in the universe. So long as you have elemental oxygen, it will react with things and hydrogen is the thing it will react with the most. So having water is almost a given for any Star system. Additionally, protoplanet and cometary collisions are in fact statistically inevitable. The real question is if water can be delivered at a point after enough gravity has amassed to ensure the water stays there.
Right, that's the sticky point? The likelihood of a planet in the Goldilocks zone to be too hot in the early stage of stabilizing its chemistry that it requires seeding with "post-formation" chemistry? Is that likelihood close to 100%, or maybe not even near and we were just set up for a funny cosmic event.
I agree. In addition to the chemical elements like water, as mentioned in the article, the impact with Theia also enabled strong magmatic activity at the core of the planet, and that was a critical element as well to sustain life.
Probably the strong magnetic activity of the Earth's core was key to maintaining the atmosphere, but also, the magmatic heat contributed to keeping the planet at a good temperature to support life when a young Sun provided significantly less radiation.
All these elements may suggest that the collision is needed to satisfy the very strict requirements about where the planet is located and about the size and composition of the colliding planet. This makes the probability for life-sustaining planets in the Drake equation extremely low.
As an indirect proof of the tightness of the condition is the fact that the Earth in its history had periods of climate extremes hostile to life, like the Snowball Earth when the planet was completely covered by ice and snow, or at the opposite extreme, the very hot periods when the greenhouse effect was dominating the climate.
If Mars contained significant amounts of water in its past as we suspect, that would mean we have n=2 just in our own solar system.
Speaking of Drake equations, you should (1) see the other comment here with this account name (2) check out the top Pirate Bay rip of Dark City (which predated that other movie) and turn on the English subtitles and count the number of times the characters look at or make gestures pointing to certain alignments of the text in the subtitles and, if you're true "hackers", try to figure out the encrypted messages in the text alignments that the characters are looking at/pointing to at key moments – and then when/if you figure out what the encrypted messages mean, try to figure out how the director worked together backwards so that they could have a script that aligns a certain way using subtitles and then make the scenes so that the actors are looking/pointing to key spots at just the right time.
If you appreciate technical things, you'd be in for a treat.
Right. It's discouraging. We now know that many stars have planets, and some of them are even in the Goldilocks zone. But if it takes a planetary collision to get water... And only one planetary collision, because each one wipes out essentially all life.
Look at the rest of the solar system. Mars - almost no water. Luna - almost no water. Venus, maybe water[1], but as steam. Too close to the sun and too hot.
[1] https://phys.org/news/2025-10-venus-clouds-reanalyzed.html
I find it incredibly encouraging. I fear aliens existing in sufficient enough quantity to find us more than I fear Earth being the only host to intelligent life until we escape it.
Probably not the only host, but habitable planets are sparse. If Einstein was right and faster than light travel is impossible, the number of planets we can even talk to is not that large. There are only 94 stellar systems within twenty light years.
Planetary collisions happen all the time. All of Mercury, Venus, Earth, and Mars in our solar system had them. We can see their signatures in other solar systems too: see https://en.wikipedia.org/wiki/List_of_extrasolar_planetary_c...
Whatever the great filter is, it's not planetary-scale collisions during the accretion phase of solar system formation.
A couple of dozen collisions out of 6000+ known exoplanets. Not exactly common, but not freakishly rare either.
Those are just the ones we caught in the act. That we can see 6,000+ means that there are many more we don't see.
This also points to panspermia.
"The hypothesis that life, in the form of “seeds” or spores, is distributed throughout the universe, traveling between planets, moons, and other bodies via space dust, asteroids, comets, and possibly even spacecraft."
I want to think that the water contained life and not the barren earth.
Bit of a nit but the Drake equation is intended 'to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy' (from the Wikipedia entry for it). Nice thing is that you can drop a few terms to get to origin of life.
Don’t forget this can only happen once, really. You need it to be such a rare event that it doesn’t keep sanitizing the planet with repeated impacts, but one really perfect strike will bring what you need and allow life to form.
The number of instances where this (something unreasonably unlikely) happened in our cosmological history is kinda surprisingly high. I’m absolutely convinced there’s no advanced life (and CERTAINLY no technological civilizations) outside of earth.
One other example: we gained most of our adaptability, curiosity, and problem solving skills as very tiny mammals while dinos ruled the earth. The only way we ever took over the planet was thanks to an asteroid wiping out all those huge creatures. Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.
Our intelligence exploded largely because that extinction event removed almost all major predators, turning earth into a giant survival puzzle sandbox for mammals to grow in.
Edit: our brains only grew big because it was the best means of survival - they’re crazy expensive, so without this “sandbox puzzle” effect, we probably never would’ve grown them.
> Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage.
Maybe it was just being small, puny, and having a tendency to cower in burrows was what saved us. Our ancestors may not have been much smarter than squirrels, and squirrels aren’t very bright.
Hominids brains didn’t get big until long, long after the KT extinction. A Tigers brain is not that much smaller than that of an an Australopithecus.
Correct - that’s what SAVED us. What allowed us to thrive and dominate the planet was what I mentioned.
It may be more correct to say that growing a larger brain (larger than a lizard’s, I mean) was only realistically possible because of the sudden loss of predators.
Earth has been struck by large comets many times killing the majority of life on the planet each time. In an early solar system it would be more frequent. Once a comet impacts there is one less comet out there. The solar system cleans up over time making impacts less likely over time.
There isn’t that much of a difference in the number of comets in space across just 5 billion years.
There's not much difference between now and 3.5-3.8 billion years ago, but before that there were a lot more: https://en.wikipedia.org/wiki/Late_Heavy_Bombardment
Especially in the context of this, I am baffled by people who go to great lengths to prevent life from Earth arriving on other solar system bodies. Such as all the efforts to sterilize the probes.
Historically to prevent pre-contamination and erroneous biosignature readings. This may ease once we have some solid pointers or confidence there may be none (caution is likely warranted due to the gravity of such a discovery).
But we also lose opportunity.
Consider Mars. Endless probes for 50 years going to Mars looking for life. No clue of life has ever been found. At what point do we face the fact that Mars is a dead rock?
What we should be doing is collecting samples of extremophiles from the Earth, and attaching a few packets of them to every probe going to Mars, and see what happens. Probably nothing will happen, but it's worth a try.
Not so much, because both Venus and Mars also have water. So whatever gave Earth water is common enough to also give it to the other inner planets.
No kidding... This would probably resolve the Fermi paradox if proven true...
A brilliant summary! You've deepened the question from "Does a habitable planet exist?" to "Does a planet successfully complete the complex dynamics of life's origin?" The habitable zone is merely the ticket, while the conditions you mention are the truly demanding filters. Considering this, the probability of our existence truly seems miraculous
Your assumption we need water for life to exist is in my opinion wrong. We only know Earth so assume that is what is needed for life to exist.
There is a hard limit on the number of atomic elements, and an even smaller limit on the number of soluble compounds that facilitate chemical reactions, and water is demonstrably both the best and the most common in the universe.
So while it may be possible for life to exist without water, any alternatives should be reasonably expected to be even more rare than water-based life
There's a reason life is carbon-based, and it's not random. It's the only element that works, due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable. There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy. And no other elements have any hope. If you have carbon-based life, you need water as solvent and medium.
It's a pretty safe assumption that all life requires water.
> There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy.
Right. Silicon dioxide is quartz.
Longer analysis.[1]
[1] https://www.the-ies.org/analysis/does-silicon-based-life-exi...
> due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable
Well, the thing is that all of those are environment-dependent.
We do have data on a somewhat diverse set of environments, and it's enough to confirm what we knew about the flexibility of carbon. But it's not enough to disprove the alternatives.
1. xbmcuser’s point: They challenge the anthropocentric (Earth-centric) assumption — “we only know life as we know it.” Philosophically valid, but scientifically weak without proposing a viable alternative chemistry.
2. joshuahedlund’s reply: Grounds the argument in chemistry and probability.
There are only ~90 stable elements → a finite combinatorial chemistry space.
Among possible solvents, water is the most abundant and chemically versatile (dipolar, wide liquid range, high heat capacity, good at dissolving ions and organics). → So even if other solvents can work (like ammonia, methane, formamide), the odds heavily favor water-based life.
3. caymanjim’s addition: Brings in carbon’s unique valence behavior:
4 valence electrons → can form stable, complex chains and rings.
Bonds are strong but not too strong → dynamic yet stable biochemistry.
Silicon (next best candidate) forms brittle, static lattices and poorly soluble oxides → bad for metabolism. → Therefore: if life is carbon-based, water is the only sensible solvent.
What's the chemistry of life without water? Do you refer to the promising Russian studies of life sustained by alcohol?
You’re getting a lot of negative feedback for whatever reason, but you’re absolutely right.
I for one remember reading about possible silicon/methane based life, etc. Actually, here’s a whole wikipedia article on what you’re talking about.
https://en.m.wikipedia.org/wiki/Hypothetical_types_of_bioche...
Perhaps HN folks will lose your scent now and direct their snark there
But when you dig down deep on theories like that it just doesn’t make sense from a chemistry or physics standpoint. Everyone saw that Star Trek episode about silicon based life and ran with it as being possible. It’s just a show.
https://en.wikipedia.org/wiki/The_Devil_in_the_Dark
https://lweb.cfa.harvard.edu/~ejchaisson/cosmic_evolution/do...
The likelihood of those criteria might be vastly different in a younger universe than in this one, no?
The Drake equation is whatever math leads to Earth being the only planet with intelligent matter out of infinity planets.
Mars is technically in the goldilocks zone of the solar system... but water on Mars boils at 0C or 32F due to low atmospheric pressure, which really sucks.
Related, a recent study suggests up to 1% of our mantle is water trapped within rock that gets released as subduction increases to higher heat and pressure. This water could account for three times the amount of water on the surface and may represent a whole-Earth water cycle.
https://www.bnl.gov/newsroom/news.php?a=111648
I wonder how this ties in with the submitted link about Theia. And it will be interesting if we ever get similar trapped water discovered in martian rock.
There are structures in Earth's mantle which are believed to be leftover chunks of Theia, which makes the connection feel quite plausible.
https://www.newscientist.com/article/2400567-bits-of-an-anci...
This reminds me of Stephen Baxter's novel "Flood"
I've tried reading the paper, which is obviously less hand wavy than this mess of a blog post but pretty tough going for a layman. I still don't see how they conclude that the water arrived all at once instead of in a bunch of comets... https://www.science.org/doi/10.1126/sciadv.adw1280
>this mess of a blog post
It's that. Just one more in a long line of wild-eyed 'the Earth collided with' theories.
> Scientists have shown that Earth’s basic chemistry solidified within just three million years ...
They haven't 'shown' anything. They may have evidence to support part of one model ... if they can demonstrate that a Theia probably existed in the first place.
Try to read it? Thick going. https://www.science.org/doi/10.1126/sciadv.adw1280. Quoting from that:
"Today’s element abundances of the BSE and isotope constraints strongly suggest that the bulk Earth comprises ~90% PE, ~10% Theia, and ~0.4% late veneer material... Other models suggest that Earth formed from ~60% PE and ~40% Theia ..."
>a later collision with Theia likely delivered the water
Etc. If water was so hard to get ... where in the hell did this hypothetical, no evidence 'likely' get the water it 'delivered'?
Water wasn't hard to get in the outer solar system. You know, where all the ice balls are?
They're not here to "demonstrate" the Theia impact theory, because there's already tons of other work doing that.
I also don't see how they disprove the contribution of gravity. Remember that Earth is composed of fifty Titan-sized bodies.
Titan, and probably Uranus and Neptune, probably have their methane etc. as a result of outgassing - initially, the volatiles are embedded in the inner rocks, but as they gravitationally differentiate and heat - and are subject to tide-like interactions with other bodies - the volatiles are released.
(The real questions are "Why does Ganymede not have an atmosphere?" and "What's up with Venus, really?")
I believe the idea is that the water was all cooked out of Earth's protoplanetary disk material before it even formed large chunks. So gravity never got a chance to "contribute" on that front.
Well, that seems to make 2 major assumptions (and several minor ones), both of which are probably false:
* that the planetesimals that formed Earth had the same orbital characteristics (notably eccentricity), rather than being averaged out.
* that planetesimals formed from dust in largely the same manner as planets form from planetesimals
...no, I don't think it makes either of those assumptions.
All at once is what explains the isotopic homogeneity (e.g. in oxygen) between the earth and the moon
Meaning not just all the water but all the oxygen came in with Theia?
The
>Our Solar System formed around 4,568 million years ago. Considering that it only took up to 3 million years to determine the chemical properties of the Earth
sounds suspiciously precise. You'd imaging the proto Earth would have formed gradually over millions of years from rocks and dust merging rather than suddenly there 4,568 m years ago and then shortly after crashed into?
Well, 3 million is "millions". Anyway, that very quote continues:
> "...this is surprisingly fast," says first author Kruttasch.
So they don't entirely disagree that it's weird.
But why are you replying to me with a quote from the article I already called a mess? Try your hand at the paper if you want real answers. :D Like I said, tough going, but they sure seem to think they have the sigfigs to back it up.
>was rich in volatile elements essential for life, such as hydrogen, carbon and sulphur.
Today years old on learning that 'carbon' is a 'volatile element'. (I come to learn that astrogeology has a unique definition of volatile).
• The summary's own source article points makes no reference to carbon being volatile.
• The wikipedia article for 'volatiles' in the astrogeological sense makes no reference to carbon being volatile https://en.wikipedia.org/wiki/Volatile_(astrogeology) . Similarly, the wikipedia article for 'refractory', posed as the astrogeological opposite of volatile, does not place carbon at all in the spectrum of volatile to refractory.
• Contra: at least two papers do refer to carbon being a volatile element. https://www.nature.com/articles/s41586-022-05276-x and https://arxiv.org/abs/2311.18262
[shrug]
I take this as “volatile” in the sense that it bonds easily with other molecules
Astrophysicsts would also call these "metals" (anything heavier than helium) so don't read too much into it. :D
https://sentinelmission.org/astrophysics-glossary/metallicit...
Thank you, that does make me feel at the same time better as an individual and sadder about my expectations for the astrophysicists’ ability to draw anything resembling reasonable conclusions about the makeup of the celestial bodies.
Interestingly, Earth scientists have long understood that plate tectonics is highly unlikely to exist on a rocky planet without water (to put it simply, water is needed to deform the Earth's upper mantle), given all that this entails. If this hypothesis is true, plate tectonics as such should be post-collision.
You can see this in Venus. No water and no plate tectonics. Instead you get heat buildup under the crust until there's a cataclysmic overturn event.
What about the Mars scientists?
The article says the light elements hydrogen, carbon and sulfur (and oxygen?) were only able to condense on the outer planets (and their moons). And the original article specifically says "the inner Solar System planets Venus and Mercury are largely devoid of volatile elements". If that's the case, why does Venus have so much carbon dioxide?
(I'm not saying the article is wrong, just trying to understand.)
> why does Venus have so much carbon dioxide?
Venus doesn't have liquid water, which is needed for the reaction of silicates with CO2 ("weathering"). Without that reaction, CO2 just accumulates in the atmosphere. Most of the carbon on Earth (and there's a lot) is locked up in rocks.
There's also a biological effect. Here on Earth, silica in the ocean is scrubbed out by microorganisms that create silica shells; these tiny shells fall out into sediments, where (in deep ocean) they eventually form a kind of biogenic rock called "chert". Elsewhere, typically in shallow water, carbonate rocks are formed from the remains of other kinds of animals. Without these effects, the dissolved silicon concentration in seawater would be orders of magnitude higher, and the silica would react to form clays. This reaction would acidify the ocean and prevent carbonate formation.
Just such "reverse weathering" has been hypothesized to occur after the Permian-Triassic boundary, where CO2 levels stayed elevated for 5 million years. The extinction event was so severe it disrupted chert formation (a "chert gap").
Keep in mind that carbon dioxide is almost 3x heavier than methane. Part of the reason Venus has "so much" CO₂ is because all the lighter gasses have been depleted.
(But yes, Venus is hard to satisfactorily explain, regardless of whether you accept the article's conclusions at face value.)
How does this square with the fact that we have solid evidence of water on Mars as well?
Having some water and having lots of water is a slight difference. The most arid dessert on earth is a jungle compared to Mars.
(Also Mars could have been also hit.)
Except Titan likely has more water on it than Earth. Therefore unless we’re a fluke of a solar system planetary bodies with water on them should be extremely common.
Titan is outside the frost line. There’s no question that there’s a huge amount of water in solar systems, the question is if there’s a consistent transport system (comets, in this case) that moves it inside the frost line to where liquid water can, given an atmosphere and gravity, exist in conditions that match our familiar conditions for life.
The article mentions that the inner planets were initially too hot to retain water, but presumably Titan didn’t have that problem, being much farther from the sun.
Titan is interesting, but much further away from the sun, so different conditions. We want earthlike conditions, life that can sustain on anything else, is just hypothesis so far.
(As is the claim from the article)
Mars is further out in the solar system, and I'm assuming it was further out than Theia when the collision occurred.
The article doesn't say no planets can have water, but just that originally Earth was too close to the Sun to have liquid water. Theia, according to this hypothesis, was not.
And also Saturn's moon Europa
So we're not only made of elements which formed inside star(s) but also ones merged from two different planets. This is weird.
In the scale of the universe this is bound to happen, likely infinite times anyway and this is what feels rather weird to me. Not just the perceived "special circumstances" but that independent of the rarity it will still happen many many times and then any conscious lifeform developing technology to realize this be subject to the definition of survivorship bias.
And the remnants of two neutron stars colliding.
As above, so below. Two humans colliding, too.
There was a giant incandescent donut involved, too. https://en.wikipedia.org/wiki/Synestia
Original paper: https://www.science.org/doi/10.1126/sciadv.adw1280
Is this the same collision theorized to have created the moon?
That's what is suggested here but according to the Giant Impact Hypothesis the impact happened about 4.5 billion years ago and formed the Moon from debris, and it likely vaporized much of any existing water on proto-Earth rather than delivering it... More investigations needed ...
Yes
What I don’t understand is how you define a single point (even if the point spans a million years) of “when the solar system formed.” They say the chemical composition of the Earth solidified “only 3 million years after the solar system formed” — isn’t the formation of the planets itself part of the formation of the solar system? How does one define the moment of formation? Or does this mean that we know with certainty that there was no physically consistent body one could identify as “Earth” 3 million years prior, and then within those 3 million years, it coalesced and solidified?
I was under the vague impression that there is a single moment when the gravitational force in the core of the proto solar system outweighs (ha!) the electromagnetic repulsion of deuterium/tritium nuclei and fusion is achieved.
The resulting radiation pressure clears out the debris from the solar system’s accretion disk, and this process surely is not instantaneous but is relatively fast.
> How does one define the moment of formation?
We don't. It's usually within a range. My illustrated book shows the timeline with more context and detail. Note that the events are provided on a timeline with some uncertainty (e.g., ± 1 million years):
https://impacts.to/downloads/lowres/impacts.pdf
That’s what I was thinking but I guess the uncertainty is less than I assumed.
Btw your book is AMAZING!
What are the chances of the Earth forming yet remaining dry?
Exoplanet surveys that I've seen in popular press can see rocky, dry planets. I'm not sure if that's just a selection bias in our current technology or if Earth with ocean and atmosphere is relatively rare.
I don't understand why all these volatiles (hydrogen, nitrogen) didn't evaporate during such huge collision, which likely melt the whole Earth's crust. Even if a temporary atmosphere was formed, with high post-impact temperatures this atmosphere can't stay long.
As far as we know, molecules and atoms escaping into space comes due to the solar wind. Somehow the solar wind activates these atoms and carries them off into the distant vacuum, ad infinitum presumably though (I would imagine) limited by the heliopause.
[edit, benefiting from convo: mechanisms on atmospheric escape, to varying degrees of verification)
• https://en.wikipedia.org/wiki/Atmospheric_escape
• https://en.wikipedia.org/wiki/Hydrodynamic_escape ]
Absent that, our treasured atmospheric molecules would have to autonomousy achieve escape velocity, some 22 km/sec , with no outside assistance. A difficult feat. And so, resident atmosphere.
With high enough temperature some molecules may achieve velocities enough to escape. The question is - how hot was it really? The initial collision happened at least with escape velocity, so there was roughly enough energy for volatiles an non-volatiles to escape. But non-volatiles condensed presumably pretty quickly (but were still hot) in comparison to volatiles.
Yes I was being a bit too glib in relegating atmospheric escape mechanisms exclusively to action by the solar wind. Lot of proposed mechanisms, uncertain how many of them are verified and quantified to what magnitude.
https://en.wikipedia.org/wiki/Atmospheric_escape
https://en.wikipedia.org/wiki/Hydrodynamic_escape
As a layperson I see our current epistemological state as long on models, and short on empirical verification (because we're talking about a difficult phenomenon to verify).
I think I mostly wanted to offer counterpoint to the original comment that 'this atmosphere can't stay long' i.e. even under elevated temperatures.
(I'll probably update my prev comment with those wikipedia links.)
I wonder how much adenine, guanine, thymine, and cytosine was present in that water.
The water also helped with cooling the surface right? And I thought this was already a widely accepted theory, that the water came from a meteor or asteroid.
Tough to gain any predictive information here due to the anthropic principle requiring a series of comical happenstance for observation to even occur.
How did water-rich Theia get its water?
Not buying it, Mars had water with no major collision.
Ah the First Impact
I know this reference lol
Imagine this sci-fi plot twist:
Aliens make live habitable by hitting proto-Earth with a planet, so life can sprout there.
They calibrated it such a way that angular size of Moon is the same as of Sun.
I would say "spoilers" ... but it's the title of the story. The Fermi Paradox Is Our Business Model
https://en.wikipedia.org/wiki/The_Fermi_Paradox_Is_Our_Busin...
https://www.tor.com/2010/08/11/the-fermi-paradox-is-our-busi...
That is pretty much the premise of Hal Clement's short story "Halo", which I read in _Space Lash_ (originally published as _Small Changes_), but now available in:
https://www.goodreads.com/book/show/939760.Music_of_Many_Sph...
I recommend folks read it in reverse chronological order, starting at the back, then working to the front and bailing when things get too quaint/old-school/golden-age.
The Moon was much closer to the Earth when it was formed. It's slowly becoming more distant.
So the angular size has matched the Sun only for 450 million years.
In 50 million years it's angular size will be smaller and total solar eclipses will be impossible.
Note: Due to the Moon's orbit, the whole story is more complicated.
I know that. But in this scenario, aliens know the timescale of appearance of life intelligent enough it can appreciate solar eclipse.
It seems we only developed in the last 90% of time during which solar eclipses are possible. Perhaps we're slow compared to our galactic sisters and brothers.
Imagine the real twist being that complex intelligent life on a planet only goes past some critical development point if there's some sort of weird coincidence in the sky that pushes its inhabitants to understand the mystery.
It's the weirdest filter: you need a giant sign that points you where to look for answers. Without it, you're less likely to find what the universe is all about.
What if they miscalculated and intelligence evolved when the moon drifted too far to cover the sun?
They regularly smashed asteroids onto earth until intelligent life emerged.
Smashing will continue until morale improves…
All life on Earth is illegal immigrants from another planet.
Sorry, I was only joking. Someone got busy seriously down voting! Maybe wrong times to utter the phrase "illegal immigrants". I get it.
Well, I for the count of one, didn't think it bad, but thought provoking. We're all immigrants, when you get deep into it (speaking from Europe, where we usurped previously native folk some 1500 years ago), and we all came from Africa anyway.
But, yeah, political implications nowadays are a slippery slope.
Only if the earth was seeded with life.
Which is possible, at least from sites elsewhere in the young solar system. Life might have originated on Mars, for example, or perhaps in one of many small, warm, wet asteroids. These early asteroids were kept from freezing up by the presence of short lived radioisotopes, the decay products of which are detectable today in parts of meteorites.
Which seems to be quite possible. This is what we have from just one mission: https://www.esa.int/Science_Exploration/Space_Science/Rosett...
Absolute garbage.
The Earth has a nearly perfect circular orbit. Any collision with another planet would have pushed it off its orbit and caused it to at the very least created a more elliptical orbit that likely would have made the swings in temperature more deadly for life on Earth.
This entire article is science fiction.
Isn't the most common scientific theory about the origin of the Moon that a big body collided with Earth?
How can it be science fiction if most scientists currently believe this?
This guy thinks he's smarter than all those scientists. Consider his opinion accordingly.
> The Earth has a nearly perfect circular orbit. Any collision with another planet would have pushed it off its orbit and caused it to at the very least created a more elliptical orbit that likely would have made the swings in temperature more deadly for life on Earth.
There is a lot of evidence of a big collision, but that's a very good question anyway!
I guess the interactions with other planets and asteroids change the orbit to a more circular one. I couldn't find a serious source that confirm, and not even a non-serious, so I'm still curious, very curious.
Anyway, there is a good theory that Jupiter formed at 3 AU and moved later to 5 AU and (very slowly) caused havoc in all the outer solar system https://en.wikipedia.org/wiki/Formation_and_evolution_of_the... So the initial orbits are not fixed in stone.
Furthermore, robotic exploration of Mars is already yielding sufficient evidence that Mars once had oceans. There is a well-founded suspicion that Europa and Titan have seas hidden beneath their surfaces. Does this article mean that all of this is just our imagination? I don't think so.
This makes some sense actually. Does anyone have a counterargument to this?
It's backwards. Highly eccentric orbits are the default; near-circular orbits are the inevitable result of averaging out a large number of orbits after they collide.
It's also ignoring the fact that we likely did have additional planets, but after interactions with other planets with nearby orbits, they would have been either ejected out of the solar system entirely, caused to collide, or herded into more circular (non-overlapping) orbits.
This is why Pluto is not a planet.
While I agree with you on most points, that is not why Pluto is not a planet.
The reason is that it was observed "too soon" because of its interaction with Neptune's orbit. Once we realized there were plenty of such objects in the range of Neptune's orbit but we also realized that these were not fully formed planets, we invented the term of dwarf planet, so Pluto was demoted to that status, which it shares with many other objects in the far out orbit.
So, it was just a classification thing. We could have also said all those others are also planets.
Science makes itself look dumb compared to creationism.
I thought the consensus was that the water came from comet impacts?
I don’t believe this.
the fact is that there are over 700 quintillion planets in the universe, habitable is over 40 billion... i think our current understanding of physics limits our ability to reach any of them.
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TLDR: Theia
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> but please trust the science!
If you're going to disparage the best idea humanity has ever had, you are required to commit and explicitly suggest your preferred alternative.
Your attempt at clever irony is a negative contribution to the world.
It is precisely the tendency of scientists to qualify their certainty that makes them worthy of our trust.
Reading comprehension: The collision with Theia likely had a large effect on Earth once it occurred, but the collision might still have been unlikely to occur in the first place.
We humans are not from Earth, what more signs need those who can't see? Humans,from all the species, the unique without a natural habitat. Humans, can not live on this planet unless we all get together and start adapting the environment. Otherwise, we can only survive and it's not fun. We have to wear clothing, cut downn trees. We get ill and stuff. Monkey us from? We closer to the pigs and not just the hips.
> We get ill and stuff
Just out of curiosity: you do realise that illness is not specific to humans, but also occurs in animals, right?
Of course, yes -hell, even cats have their own AIDS; but what I meant was we get 'easily' ill. I mean, imagine we have to drink the water from a puddle?
What?
You heard the man! Monkey us from?
Hey that bit was for the lols, although it is quite valid to say, just missing plural and a comma. Innacurate in some ways -mainstream theory is not about coming from apes, rather is about sharing a, yet undiscovered, common ancestor. I mentionned the pigs because of promising advancement in organ transplantation, notably kidneys that reached a milesone recently, and I mentionned the hips because human hips and ape hips have an evolution-breaking distinction. I could go on and on, but let's wait for more science, it wouldn't surprise me that what knowledge we discovered and took for granted back then, when 80% of the world population did not know how to read, might be developped today.
I really appreciate your open response! Your writing style is so fascinating, it reminds me of how my dad used to talk (he was Persian, not a native English speaker). What’s your background? How did you end up with these beliefs?
Thanks for the kind words. My heart is Belgian and I'm living in Panama now; Well, I always wondered why we 'evolved to die', in the sense that from my understanding, the initial life forms, quasi-minerals, wouldn't die of old age, just of trauma like cell rutpture or something. There is so much to say so I really cut it short, but eventually I read about how it was probable that first living things came from an asteroid, I started thinking that 'something', call it God if its meaning hasn't been perverted by manmade things, put us there. Something currently above our understanding, and quite extraordinary -what kind of energy to run the universe.
Yes.
From a purely mathematical, scientific, and logical standpoint, I must regard this article as entirely speculative. The scientific claims it presents are extraordinarily improbable, and sound reasoning compels their complete dismissal.
History repeatedly shows that the popular: "extraordinary claims demand extraordinary evidence" is often dependent on the frame of reference.
What is thought to be likely is used to frame conventional wisdom as truth, making the new viewpoint "extraordinary, until, over and over again, the new viewpoint becomes conventional wisdom. So "extraordinarily improbable" is really just an overton window framing (what we accept/don't accept), rather than a statement based in logic. Though your overall framing reminds me so much of historical phrases that I wonder if you are being intentionally ironic.
Claude Sonnet 4.5 summary of the original paper [https://www.science.org/doi/10.1126/sciadv.adw1280] for middle school students:
How Earth Got Its Water: A Cosmic Detective Story
The Big Question: How did Earth become a planet with oceans and life, when it formed so close to the hot Sun?
What Scientists Did:
- They used a "radioactive clock" made from two elements: manganese and chromium - Manganese-53 breaks down into chromium-53 over time (like ice melting at a steady rate) - By measuring these elements in meteorites and Earth rocks, they figured out WHEN Earth's basic chemistry was locked in
Key Finding: Earth's chemical recipe was set within just 3 million years after the Solar System formed (that's super fast in space terms!)
The Problem: At that point, early Earth was missing the ingredients for life—especially water, carbon, and other "volatile elements" (stuff that evaporates easily when hot)
Why Earth Was Dry: Close to the Sun, it was too hot for water and other volatile stuff to stick to the rocks that built Earth—they stayed as gas and floated away
The Solution: About 70 million years later, another planet called Theia (which formed farther from the Sun where it was cooler) crashed into Earth:
This collision created our Moon It also delivered water and other life-essential ingredients to Earth
The Big Takeaway: Earth needed a cosmic accident to become livable. Without that lucky collision bringing water from the outer Solar System, we wouldn't be here!
Why This Matters: If Earth needed such specific, lucky events to support life, habitable planets like ours might be much rarer in the universe than we thought.