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>Microbial life fossils But since the RNA world is still poorly understood, and the nature of the lifeforms is highly speculative, there are many possible expl

>Microbial life fossils 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.

adastra22 4y ago
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.
- mtlmtlmtlmtl 4y ago
  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.
  - adastra22 4y ago
    Likewise! 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 :(

adastra22 4y ago

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.

mtlmtlmtlmtl 4y ago
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.
- adastra22 4y ago
  Likewise! 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 :(