Oldest terran fossils?

[Black Globe Generator]

3.4 billion year old fossil stromatolites in Australia

Many of the worlds IMTU tend to have simple life forms like stromatolites and other microbial life - more complex organisms tend to be rare, and the introduction of species as a part of a terraforming program rather common.

 

[Mickazoid]

Also google 'panspermia'. Interesting possibilities for biological distribution on a cosmic scale.

Basically - microbacteria can be propelled on solar winds and can withstand reentry within rock and icy masses. Allows biological diversity, but overcomes the 'how does primordial life happen on all these worlds completely independently' issue I've never seen well-resolved.

 

[Chaos]

AFAIK the panspermia theory has been more or less discarded, because microbacteria, although they might survive re-entry, could never survive being bombarded with hard radiation for millions upon millions of years. Nor could they, if sealed up within rock and icy masses, survive *impact*.

The solution to the "how does primordial life arise completely independently" issue could be a combination of two factors:
- one, that the steps that lead to life happen very often, so that, whereever the environment is even marginally conducive to life, it is almost given that it will arise (AFAIK this is very much accepted by science nowadays)
- two, that there are only so many viable solutions to problem (viable in an evolutionary sense, not a purely theoretical sense), so that similar problems tend to lead to similar solution - almost everything you see in life has evolved independently several times; the eye, for example, some 25 or 30 times, IIRC, wings six or eight times, even exotic stuff like echolocation evolved independently at least twice.

 

[Stainless]

I was invited to a NASA-sponsored meeting at Wood's Hole about 8 years ago (it was entitled something like "Forefront of evolution"). Bill Schopf was there with his, then, relatively new evidence of cyanobacterial-like fossils in South Australian rocks (Flinder's Ranges). Over some beers one night, the assembled experts all agreed that panspermia seems a quite valid explanation for the sudden appearance of life on Earth. After all, it appears to have arisen almost as soon as the planet cooled sufficiently to harbour it.

Yes, it is a problem to explain how life could pass through interstellar space for millions of years and arrive on Earth in a viable state. However, we know that extant bacterial species can form extremely stable endospores. These are highly resistant to radiation. There is at least one bacterium (Deinococcus radiodurans) that survives exremely high levels of gamma radiation. Its genome is constantly being broken up and it happily repairs it. Quite a curious bug in other ways as well. Vacuum and cold poses no problems to most bacteria as we routinely store bacteria and archaea as freeze-dried samples in vacuum sealed glass vials. Lastly, the genomes of the initial organisms may have been very small. Since that presents a small target and there are relatively low radiation levels per unit area in deep space (despite a long time there), I can envisage something surviving. Arguably it takes only one asexually reproducing organism to kickstart everything we see today.

 

[Chaos]

Interesting... I didn´t know about this.

On the other hand, from what I´ve heard about experiments trying to duplicate conditions on primordial Earth, the amino acids were being created practically fast enough for the scientists to watch the process. Well, not quite, but when the experiements were stopped after (IIRC) a couple of weeks, they already had a few simple amino acids.
And even if we were talking about a few million years from the basic chemicals (CH4, NH3, H2O, CO2, H2 - anything else?) to the first lifeforms, that would still fit the description of "almost as soon as the planet cooled sufficiently", as seen from now.

 

[Stainless]

Oparin & Haldane both proposed a primordial soup origin of life. Miller & Urey showed you could get organic molecules from an artificial primordial atmosphere system. However, going from a soup of racemic organic molecules to a self-replicating system is quite a task despite what many would say. I know. I still have the record for the smallest ribozyme experiment and have been in and around the area for the past 15 years. Don't get me wrong, I'm not espousing any intelligent design stuff. Just pointing out that this whole area happened so far back, and is full of so much speculation, that it eventually just degrades into "cocktail party conversation" stuff. Life could have started here, it could have started elsewhere. Doesn't really matter, as it had to start somewhere.

 

[Malenfant]

One thing I don't get about Panspermia is that it does nothing to explain how life arose. It just says that life arrived on Earth from elsewhere, but where did that life come from?

I don't believe a word of it myself. If it was true, then surely you'd expect to find viable alien micro-organisms in meteorites - and we don't. I think it's much more believable that life just simply arises naturally given the right chemical conditions.

 

[aramis]

With panspermia, one only needs life to arise rarely to have a universe filled with life.

Without, lots of pre-biotic worlds might just sit until contact.

Of course, a self replicating molecule needs only EVOLVE once per world provided it "lives" long enough to replicate.

 

[Malenfant]

Originally posted by Aramis:
With panspermia, one only needs life to arise rarely to have a universe filled with life.

It still dodges the question of where life first arose and how it came about.

I just don't think there's any historical (in the geological evidence) to support the idea either. Life formed on Earth pretty much as soon as things had calmed down enough to allow it to survive. A logical first assumption to make from that is that life was a natural consequence of the conditions that were present at the time, but it doesn't imply at all that it came from elsewhere.

 

[FlightCommanderSolitude]

I also find the panspermia notion unsatisfying, if interesting from a "what if" perspective.

I believe that there's evidence (which, as luck would have it, is not at my fingertips) that microbial life arose on Earth several times, each time ultimately failing, until it finally "stuck" and began to complexify.

If true, it would imply that life is very likely to arise in the right conditions.

 

[Mickazoid]

I believe that life is likely to arise from the right chemical and environmental conditions, and that it appears able to be distributed between worlds as well by geologic/cosmic events. Panspermia does not preclude spontaneous biogenesis. The universe is stranger than we can imagine, remember?

To prove that the vacuum of space serves to isolate biology to entirely separate worlds would be a very difficult thing indeed. Based on my view of the universe, it's far more likely that life can (and has) travelled before...

 

[Malenfant]

Originally posted by mickazoid:
To prove that the vacuum of space serves to isolate biology to entirely separate worlds would be a very difficult thing indeed.[/QB]

And it's any easier to prove that life HAS travelled from world to world? There's a lot to suggest that it hasn't and cannot. And while people can claim that the chance of life arising on Earth is very very low indeed, then what are the chances that our solar system just happened to be in the path of a few asteroids that travelled through interstellar space to hit the Earth and deposit life?

The only way to prove that was the case is to go out there and actually find life that is identical to our own and that absolutely cannot have gotten there by any other means. And the only way to test that would be to examine the deep genetics of that other ecosphere, since life on both that world and our own would have diverged billions of years ago.

 

[Mickazoid]

You're welcome to claim a 'side', but I simply don't believe there is a burden of proof either way on this issue. Life could easily be part of the cosmic fabric, not required to exist solely on a single world without interaction with other worlds. Examples of totally isolated systems are rare in nature.

I don't claim the chance of life is low at all. I think you are projecting alot of things on me that I do not believe.

And life (DNA) doesn't do 'identical' for long on a species level. Only slightly more frequently does it do 'identical' between individuals - so requiring life to be 'identical' won't wash in a practical context.

I'll say it again - the idea that life arose here on it's own, and the idea that life may be capable of being transplanted by natural means across the vacuum of space are NOT in conflict - and neither is proven.

 

[aramis]

Actually, Mal, the only requisite proof for panspermia would be an asteroid or comet with viable archaea inside.

By capturing live archaea in a falling chunk of matter which has been in space, we would have proof that not only can they, but they do survive ejection and reentry.

How likely is it to catch such an item? Not bloody likely. I'm certain you know those odds better than I do.

Personally, I don't buy panspermia. After all, given a billion years or so, in the chemical soup, it's quite likely to spontaneously generate at least once. Further, DNA is quite likely a universal. DNA on other worlds would prove little.

If there is Panspermia, I prefer to think of it not as natural, but as accidents of the old ones.

 

[Malenfant]

Originally posted by mickazoid:
I'll say it again - the idea that life arose here on it's own, and the idea that life may be capable of being transplanted by natural means across the vacuum of space are NOT in conflict - and neither is proven.

Those specific ideas aren't in conflict, but that's not what I'm arguing

. It's the idea that life started here BECAUSE it fell from space that is in conflict with the idea that it started naturally in situ on Earth's surface.

Life may well be able to survive in some form in interstellar space. I'm just not remotely convinced (a) that it can survive being deposited on a planet in the first place and (b) that this is how life started on Earth.

 

[Mickazoid]

I imply no such causality. I agree completely there's scant (if any) evidence that is even 'solidly circumstantial' to proving that.

Some of the prior comments above point out some strong indications (and there's the 'Mars rock' as the most public example under scrutiny), but none of it is at all indicative that 'life here began out there'.

Glad we agree on this Mal. I think I'll get used to your 'engines full' approach

 

[Malenfant]

Originally posted by mickazoid:
Glad we agree on this Mal. I think I'll get used to your 'engines full' approach

Thanks, I think?

(I'm not entirely sure what "engines full approach" means here really, I prefer to think of my approach as that of a big rock coming out of a mass-driver at ridiculous speeds

- blunt as hell but it gets the job done

)

 

[Mickazoid]

That's what I meant. However, it's not the right tool for, say, needlepoint.

 

[Stainless]

See, the point I was making! Cocktail party conversation (and lost the Traveller plot long ago!)

Point of clarification for Aaramis. The best rooting of the tree of Life we have (from paralogue rooting techniques) shows that the Domain Archaea are a branch off from the lineage that gave us Domain Eukarya. True, many of the Archaea are extremophiles, but as I've just made the point to my students, the majority are most likely non-extreme. Anything coming to our planet must have resembled at least the Cenancestor, if not been effectively the Progenote itself. That entity would be vey simple indeed.

 

[archhealer]

Obviously, a bizarre misjump resulted in a small, rickety merchang ship landing on primitive earth, one of the spaceers coughed, and they left, trying to find their way back to 'known' space, not being aware they'd travelled in time...