Panspermia and the earliest common ancestor

[Jutter]

Finally aquired my copy of Dawkins' "The ancestor's tale" (english version; I avoid translations if possible). In this book he works his way from humans to the earliest lifeform, that all current lifeforms have in common. In the first chapter he proposes that this earliest ancestor is bound to be younger than the oldest known bacteria (or fossilized traces of bacteria if you prefer).
So anyways, that got me thinking about the panspermia hypothesys, which makes the origin of life on earth a matter of vertilization from outer space rather than abiogenesis on earth. Considering what's said in that first chapter of "the ancestor's tale", panspermia would involve micro-organisms capable of surviving something as extreme as space travel... but not the evolutionary process they triggered after landing on earth.

Does anyone here have thoughts on this subject?

[Solitary]

I don't understand why they couldn't be the start of evolution, but he is a brilliant biologist, and if he says so I tend to believe him.  Solitary

[aitm]

Is this our own "infinite regression" or perhaps more likely finite regression? Did the earth give rise to new atoms? I was under the impression that all the atoms that exist today would be the same as they were in the beginning, albeit changes as they do naturally. But did earth through some process form new atoms and thus new material? If not, then obviously all atoms and matter came from space so the reality it seems is "life" in its simplest form is, was and has always been part of the cosmos. Drowning was never possible until something that could drown evolved. The stuff to make it was always here, or not.

[stromboli]

From Scientific American:
http://blogs.scientificamerican.com/life-unbounded/2012/10/15/the-panspermia-paradox/

But this doesn’t mean that interstellar, galactic panspermia isn’t still relevant. It might be happening. And this gets me to the paradox of the title. There is a factor about large-scale panspermia that to my knowledge is rarely considered, and that is natural selection. You and I, or fluffy bunnies and daffodils are all unlikely candidates for interplanetary or interstellar transferral. The sequence of events involved in panspermia will weed out all but the toughest or most serendipitously suited organisms. So, let’s suppose that galactic panspermia has really been going on for the past ten billion years or so – what do we end up with?

Although it involves a complex web of factors, it seems likely that life driven by cosmic dispersal will probably end up being completely dominated by the super-hardy, spore-forming, radiation resistant, chemical-eating, and long-lived but prolific type of critters. There may be no advantage to a particularly diverse gene pool. Billions of years of galactic transferral will have whittled it down to only the most indelicate and non-fussy microbes – super efficient, super persistent, and ubiquitous – the galactic top dogs.

Now, we might argue that there are organisms on Earth that could fit the bill, and could represent the most direct descendents of these ancient interlopers. Slow-living, low-metabolism chemoautotrophs abound, and our knowledge about these proverbial bottom-feeders is still very limited.

But the problem, and the potential paradox, is that if evolved galactic panspermia is real it’ll be capable of living  just about everywhere. There should be stuff on the Moon, Mars, Europa, Ganymede, Titan, Enceladus, even minor planets and cometary nuclei. Every icy nook and cranny in our solar system should be a veritable paradise for these ultra-tough lifeforms, honed by natural selection to make the most of appalling conditions. So if galactic panspermia exists why haven’t we noticed it yet?

There are all sorts of plausible reasons. The simplest is that we’ve not yet managed to look very hard in all these places. It’s also possible that we’ve just not put two and two together while studying the properties of terrestrial extremophilic organisms. But suppose we keep looking hard and find nothing – this would argue strongly against the possibility of galactic panspermia at all. And this would be interesting, because it would also serve to place a limit to the true extremes of life, a physical and chemical boundary condition. Perhaps the root cause turns out to be gravitational dynamics (interstellar transfer may be horrendously inefficient), or just the environmental limits of bio-chemistry and the molecular machines at the core of it all. In either case a null result might actually tell us something vitally important about the phenomena of life, and our own cosmic significance.

This is an endlessly debatable topic, because we don't know all the parameters within which life forms or the chemical precursors for life, could be transferred from place to place. Something existing inside a meteorite, shielded from cosmic radiation would allow for diversity when delivered to a planet, or not.

As the article indicated, the sheer diversity of life argues against an established, space hardy life form. But then again, we don't know all the parameters from which life could occur.