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Imperial Interstellar Scout Service Details of the worlds of the Imperium (and beyond).

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  #1  
Old June 8th, 2006, 12:14 AM
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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.
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Old June 8th, 2006, 01:12 AM
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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.
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Old June 8th, 2006, 05:12 AM
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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.
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Old June 8th, 2006, 05:44 AM
Stainless Stainless is offline
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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.
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Old June 8th, 2006, 06:53 AM
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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.
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Old June 8th, 2006, 08:37 AM
Stainless Stainless is offline
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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.
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Old June 8th, 2006, 09:52 AM
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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.
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Old June 8th, 2006, 01:08 PM
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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.
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Old June 8th, 2006, 02:24 PM
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Quote:
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.
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Old June 8th, 2006, 04:11 PM
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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.
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