It's pretty lucky that we're in a solar system with 2 other rocky planets that have some subset of the conditions for (complex) life, but not all the ones on the Earth.
Should make outstanding problems like abiogenesis easier to solve in the long run to have these worlds to compare to. We're finally getting to a really interesting phase of that research on Mars with the sample return program. And Venus is just starting to kick off with renewed interest from the field.
Then there are several icy moons that are also interesting data points, but much further away in terms of serious, in-depth(pun intended) exploration.
Id bet that having two other planets that were habitable in the early system is why the Earth developed complex life. These planets aren’t closed systems but instead they constantly (in astronomical terms) flung matter back and forth.
There's a very, very good chance that we are actually Martian life. There is absolutely no evidence whatsoever anywhere on earth for life less complex than eukaryotic cells. LUCA, the last-universal-common-ancestor of all life on Earth, is hypothesized to have been fiendishly complex with some 350 genes. Part of the difficulty of studying abiogenesis is that there is literally no evidence for or remnants of any simpler / earlier kind of life anywhere on Earth. Evidence of this kind of microbial life appears out of the blue not long after the Earth cools from the Moon-forming Thea impact. These specific genes are evidence that LUCA was a rock-boring microbe of exactly the sort that would have survived a Mars-Earth transfer event like ALH-84001. And Mars, during this time, had been warm and wet for a hundred million years or so longer than the Earth.
I would bet money that we're dependents of Martian microbes.
I'm very sceptical of this. It's a distinct possibility, and it's even pretty likely, but I don't think Earth based abiogenesis is even close to being seen as unlikely. It's still the simpler explanation in my opinion. The lack of fossils is not too convincing since microbes don't fossilise well. And it's entirely possible that life from the RNA world was just outcompeted by prokaryotic, DNA-based life. There's also the question of RNA viruses and viroids, which could be descendants of the RNA world.
Microbial life doesn't fossilize well, but the earliest secondary fossils we do have are of microbial mats. They exactly match in all respects certain microbial mat living fossils we see on the ocean today, produced by relatively complex life forms.
Most hypothecated pathways for abiogenesis would have left similar secondary fossils in the geologic record. Yet we don't see them. There's not a lot of rock left from that long ago, so maybe it just didn't get preserved. But it is striking and unexpected how (1) the earliest fossils are of quite complex organisms; (2) they pop into existence very soon after the Earth cools; yet (3) they don't evolve into any more complex patterns until hundreds of millions of years later.
So life evolved quickly (10's of millions of years), rapidly developed complex features, then whatever evolutionary force drove that suddenly stopped and they stayed stable and unchanged for half a billion years?
It is actually a simpler supposition that life evolved on Mars (or Venus, but panspermia from Mars is more likely), and a relatively complex LUCA was transferred to newly reformed Earth via an impact event. This explains all of the oddities around LUCA and the fossil record of the origin of life on Earth. Mars would have had a vibrant early-life ecosystem that provided an evolutionary push for complexity. LUCA, on the other hand, colonized a lifeless Eden and was able to spend 100's of millions of years without evolutionary pressures. And as the science surrounding ALH-84001 shows, panspermia is not an unlikely event at all. If there was life on Mars at all, it absolutely would have been transferred.
But since the RNA world is still poorly understood, and the nature of the lifeforms is highly speculative, there are many possible explanations for this consistent with an Earth origin. For instance it could be that RNA life didn't form microbial mats, or was geographically much more limited(perhaps only existing in deep sea vents, much more dependant on chemistry from the environment) until colonising the rest of the ocean later, leading to a much stronger signal in the fossil record. The RNA world might have been much shorter lived too for reason I'll get back to.
>popping into existence and only complexifying after hundreds of My
One very plausible explanation for this apparent lag is that the evolution of eukaryotes was a very unlikely event like endosymbiosis. Couple with the fact that RNA based life would be much more genetically unstable, allowing to evolve faster, and might have been much more fragile, representing a stronger selective pressure. Whereas DNA based prokaryotes are extremely versatile, which is clear from the fact that they've colonised the entire planet and lived through more drastic changes in climate than any other life form on earth.
There's also no reason that I know of to think Mars was a more(or less) likely location for abiogenesis to have occured than Earth was. More and more evidence is suggesting that the building blocks for RNA are quite abundant even sans planets, and that abiogenesis itself might actually be very likely, but later complexification might not be.
I think both hypotheses have a lot of merit. Although I will say if we find life on Mars and it turns out we are Martians I will be disappointed, because it would mean we still only have one sample of life.
There's also a possibility that there was life on mars seeded from Earth, some of which came back to us fossilised, though I'm still undecided on whether ALH-84001 contains any fossils or not. There doesn't seem to be much consensus there.
The situation with possible fossil life on ALH-84001 is one where if you are seeking consensus you probably have to wait until all the existing astrobiologists retire or die off. Having met and talked through the evidence with some of the principle people involved in that investigation, I'm personally convinced that the evidence for fossil life is very strong and the present criticisms miss the mark. But the announcement was so mishandled and politicized that continuing to fight that battle would be career-ending for all but the most senior scientists.
Regardless though, the fossils are not what I was referring to, but rather the simulations confirmed with mineral analysis which showed that the interior or ALH-84001 was never heated to more than 40 deg C (iirc) during its entire journey from Mars to the antarctic, and that had life been in the rock it would have survived the journey.
I'm leaning towards it being life myself. I just wish there was way kore of a smoking gun there than there seems to bez though there's a lot of tantalising circumstantial evidence
I suppose in the end it might actually be settled by the sample return mission, if similar fossils or even living microbes are found.
Agreed that the announcement was extremely mishandled, as has seemingly become a tradition in astrobiology.
Every major announcement like this har turned out to either be completely false(Martian canals, macroscopic life in Venera images from Venus, extremophiles with arsenic in the genetic code), or much less cut and dry than it seemed(ALH, phosphine on Venus).
Also just wanted to say, it's so nice to have a discussion like this where we disagree but in a civil manner and exchange interesting thoughts. It's a rare thing these days, so thank you.
Unfortunately I don't think the sample return mission is likely to settle this. Any extant life is probably underground to avoid the harsh radiation and hostile chemical environment of the surface. Especially now that we know there is a lot of underground ice, and almost certainly liquid aquifers. I think we'll need to send people to get access to those and sample water sources that are likely to have life. Maybe it will turn up a fossil though!
Regarding astrobiology announcements, I think the source of the problem is the refocusing on the search for life as a core nasa mission. That happened after congress turned against Mars exploration in the early 90's, as someone politically astute figured out that was a strong enough justification to keep funding. But frustratingly it became the only viable reason for exploration, and therefore a lot of money and reputation is on stake for anyone who can deliver an astrobiology win. All that pressure leads to hyped up press announcements for early results that haven't been confirmed.
I was working at the NASA Astrobiology Institute when the arsenic extremophile announcement was made, and perhaps my views are a bit colored from that. I thought we handled it alright with the information that we had, but it was just one study that hadn't been adequately replicated or peer reviewed. There was just so much pressure to get out ahead with our own announcement rather than have the story break on its own. Getting further review requires public sharing of knowledge, so I'm not sure what the right approach is :(
Parasites in general undergo simplification, they reduce and eventually lose the functionality that the host provides for them.
In my opinion this is the case in viruses, that they are so simple not because they are remnants of ancient life, but because that they are parasites that underwent secondary simplification.
The core life elements (H), C, O, N were produced by the first generation of stars. A rocky planet surface is almost all just silica on the other hand.
I don't think that post is very interesting from an origin of life perspective. The factors which limit genome growth would not have been in play at the origin of life. If the RNA origin theory of life is correct, then our oldest ancestors were replicating pieces of RNA in some sort of primordial soup. In that environment there would have been pieces of RNA everywhere whizzing about, combing, recombining, and replicating. There would have been explosive growth in "genome" size in very short amount of time, because changes would be spontaneously happening without the need for slow cycles of mutation and natural selection, which would come to dominate later.
Do you have a good link about LUCA genes looking like a rock-boring microbe? That still sounds vaguely consistent with earth-based abiogenesis, but interesting for sure.
I’m having trouble finding an article to back up my claim, so I fear I must be misremembering. Current consensus seems to be that LUCA was part of the hydrothermal vent ecosystem.
Right, I'm not a microbiologist, but it seemed like similar genes might be involved for chemoautotrophy(?) that we would expect in early earth-based life at a vent system as for rock-boring microbes that could survive a trip from Mars to Earth. I appreciate you replying, though. :)
Mars is smaller so it cooled faster after formation. Also with its thicker early atmosphere it probably was at just the right distance from the sun to be what we would consider an ideal temperature, even accounting for the dimmer sun at the time. Finally, Earth was shattered by the Moon-forming collision with Thea, which basically reset the cooldown clock for our planet. All these factors together mean that Mars had a heck of a head start.
There was a debate about whether it really couldn't be better explained by something other than life, then there was a debate as to whether they actually detected phosphine in the first place. See, for example, https://www.washington.edu/news/2021/01/27/phosphine-venus-s...
Venus is much, much less studied than Mars. Partially because of the thick athmosphere making it hard to "look at", and mostly because equipment landed on Venus(mostly by the Soviets from the 60s through the 80s) has quickly deteriorated and lost contact due to the extremely acidic environment.
But it does seem like recent research suggests Venus may have had a liquid ocean of water about 3bn years ago before a runaway greenhouse effect occured, making it too hot.
Edit: Did some reading on it, and turns out the USSR did Venus landers well into the 80s, not just the 60s. Corrected that.
Interesting. Venus research could use a bump. I did read ideas on HN talking about floating balloon probes. The density of its atmosphere allows for some interesting techniques to try out.
Maybe we should cover the outer surface of the ships in a carbonate calcium crust or marine shells so they last a little more and see if something comes dinner. Our gut is extremely acidic but there are still some adapted organisms able to live inside.
Should make outstanding problems like abiogenesis easier to solve in the long run to have these worlds to compare to. We're finally getting to a really interesting phase of that research on Mars with the sample return program. And Venus is just starting to kick off with renewed interest from the field.
Then there are several icy moons that are also interesting data points, but much further away in terms of serious, in-depth(pun intended) exploration.
I would bet money that we're dependents of Martian microbes.
Most hypothecated pathways for abiogenesis would have left similar secondary fossils in the geologic record. Yet we don't see them. There's not a lot of rock left from that long ago, so maybe it just didn't get preserved. But it is striking and unexpected how (1) the earliest fossils are of quite complex organisms; (2) they pop into existence very soon after the Earth cools; yet (3) they don't evolve into any more complex patterns until hundreds of millions of years later.
So life evolved quickly (10's of millions of years), rapidly developed complex features, then whatever evolutionary force drove that suddenly stopped and they stayed stable and unchanged for half a billion years?
It is actually a simpler supposition that life evolved on Mars (or Venus, but panspermia from Mars is more likely), and a relatively complex LUCA was transferred to newly reformed Earth via an impact event. This explains all of the oddities around LUCA and the fossil record of the origin of life on Earth. Mars would have had a vibrant early-life ecosystem that provided an evolutionary push for complexity. LUCA, on the other hand, colonized a lifeless Eden and was able to spend 100's of millions of years without evolutionary pressures. And as the science surrounding ALH-84001 shows, panspermia is not an unlikely event at all. If there was life on Mars at all, it absolutely would have been transferred.
But since the RNA world is still poorly understood, and the nature of the lifeforms is highly speculative, there are many possible explanations for this consistent with an Earth origin. For instance it could be that RNA life didn't form microbial mats, or was geographically much more limited(perhaps only existing in deep sea vents, much more dependant on chemistry from the environment) until colonising the rest of the ocean later, leading to a much stronger signal in the fossil record. The RNA world might have been much shorter lived too for reason I'll get back to.
>popping into existence and only complexifying after hundreds of My
One very plausible explanation for this apparent lag is that the evolution of eukaryotes was a very unlikely event like endosymbiosis. Couple with the fact that RNA based life would be much more genetically unstable, allowing to evolve faster, and might have been much more fragile, representing a stronger selective pressure. Whereas DNA based prokaryotes are extremely versatile, which is clear from the fact that they've colonised the entire planet and lived through more drastic changes in climate than any other life form on earth.
There's also no reason that I know of to think Mars was a more(or less) likely location for abiogenesis to have occured than Earth was. More and more evidence is suggesting that the building blocks for RNA are quite abundant even sans planets, and that abiogenesis itself might actually be very likely, but later complexification might not be.
I think both hypotheses have a lot of merit. Although I will say if we find life on Mars and it turns out we are Martians I will be disappointed, because it would mean we still only have one sample of life.
There's also a possibility that there was life on mars seeded from Earth, some of which came back to us fossilised, though I'm still undecided on whether ALH-84001 contains any fossils or not. There doesn't seem to be much consensus there.
Regardless though, the fossils are not what I was referring to, but rather the simulations confirmed with mineral analysis which showed that the interior or ALH-84001 was never heated to more than 40 deg C (iirc) during its entire journey from Mars to the antarctic, and that had life been in the rock it would have survived the journey.
I suppose in the end it might actually be settled by the sample return mission, if similar fossils or even living microbes are found.
Agreed that the announcement was extremely mishandled, as has seemingly become a tradition in astrobiology.
Every major announcement like this har turned out to either be completely false(Martian canals, macroscopic life in Venera images from Venus, extremophiles with arsenic in the genetic code), or much less cut and dry than it seemed(ALH, phosphine on Venus).
Also just wanted to say, it's so nice to have a discussion like this where we disagree but in a civil manner and exchange interesting thoughts. It's a rare thing these days, so thank you.
Unfortunately I don't think the sample return mission is likely to settle this. Any extant life is probably underground to avoid the harsh radiation and hostile chemical environment of the surface. Especially now that we know there is a lot of underground ice, and almost certainly liquid aquifers. I think we'll need to send people to get access to those and sample water sources that are likely to have life. Maybe it will turn up a fossil though!
Regarding astrobiology announcements, I think the source of the problem is the refocusing on the search for life as a core nasa mission. That happened after congress turned against Mars exploration in the early 90's, as someone politically astute figured out that was a strong enough justification to keep funding. But frustratingly it became the only viable reason for exploration, and therefore a lot of money and reputation is on stake for anyone who can deliver an astrobiology win. All that pressure leads to hyped up press announcements for early results that haven't been confirmed.
I was working at the NASA Astrobiology Institute when the arsenic extremophile announcement was made, and perhaps my views are a bit colored from that. I thought we handled it alright with the information that we had, but it was just one study that hadn't been adequately replicated or peer reviewed. There was just so much pressure to get out ahead with our own announcement rather than have the story break on its own. Getting further review requires public sharing of knowledge, so I'm not sure what the right approach is :(
In my opinion this is the case in viruses, that they are so simple not because they are remnants of ancient life, but because that they are parasites that underwent secondary simplification.
The core life elements (H), C, O, N were produced by the first generation of stars. A rocky planet surface is almost all just silica on the other hand.
I'm not sure what you meant to say here, but this is absolutely false. Prokaryotes abound.
But it does seem like recent research suggests Venus may have had a liquid ocean of water about 3bn years ago before a runaway greenhouse effect occured, making it too hot.
Edit: Did some reading on it, and turns out the USSR did Venus landers well into the 80s, not just the 60s. Corrected that.
(More serious, I think there was a brief period where conditions were more favorable on Venus, but afaik that is more in the realm of speculation)