Evidence of an oceanic impact and megatsunami on Mars
gizmodo.com
gizmodo.com
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)