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October 13, 2008


I suppose it must be viewed as Bayesian evidence for ET origin over its alternatives, but:

(a) hitchhiking from star to star *would* be just a tad more difficult, as I understand it, and more likely to revolve around passive travel than actual reproduction en route, so this isn't quite as relevant as it seems;

(b) life has to originate somewhere, and I'm not sure that saying "it originated here on Earth, in particular" is so much more improbable than "it originated elsewhere" + "it managed to hitchhike without intelligence"; and

(c) anything that makes origin-of-life easier makes the Fermi Paradox worse.

Stars pass close enough to each other often enough as to swap some of their comet clouds, and reproduction would be needed to counter natural decay I think. The easier is travel relative to origination, the more likely we are to be the result of rare origination plus less rare travel.

Care to speculate on the odds of accidental contamination versus intentional seeding?

Beauty! Another bit of evidence in favor of 'hot deep rock' and clay origin theories.

I want a flagellum to help me navigate along chemical gradients.

On the contrary, doesn't its highly specific adaptation to the highly specific environment where it was discovered add weight to the simpler hypothesis that it does *not* belong to the much wider possibility space of extra-terrestrial origins?

Robin, I don't quite see the chain of argument. Is the argument that there's sufficient evidence to suggest that these guys are descendants of visitors from other stars or just that these guys show that interstellar travel is possible, thus raising our odds that that could have been our origin?

From the references you posted, it looks like d. audaxviator picked up some of their extremophile characteristics from horizontal transmission as they descended to their current depth. So I read it as an argument about possibility. What are the other steps in the syllogism that convince you that terran life started elsewhere?

I'd hold off on the celebration until geneticists have some evidence for the direction of descent— whether other Earth organisms have vestigial DNA from D. audaxviator, or vice versa...

c) anything that makes origin-of-life easier makes the Fermi Paradox worse.

Worse because it means that intelligent life is more likely to destroy itself?

It would seem to me that if life has to originate in comets and then migrate accidentally to a "Goldilocks" planet to develop intelligence, that might actually make the Fermi Paradox less bad.

You might want to read "Rare Earth: Why Complex Life Is Uncommon in the Universe" by Peter Ward & Donald Brownlee; they suggest that simple life, on the order of bacteria may be fairly common, but that the series of advances to get eukaryotic life, then multicellular, then animals, then intelligence is each extremely improbable.

Non sequitur. In what way does this discovery cause you to increase the likelihood that life came from elsewhere?

Does D. audaxviator use a different heritability system or something? No (if it did, that surely would have been mentioned in the article).

It descended from the same ancestors as all living things here on the surface. At some point it got isolated (by rock / continental movement, for example) and lives in a very extreme environment, that selected for a very unique and narrow phenotype.

Interesting for sure. But how does this confirm panspermia?

And really, the second quote you provided is a non sequitur of the point you are trying to make re "If life starts only on planets..."

Eliezer said, "I suppose it must be viewed as Bayesian evidence for ET origin over its alternatives"

Umm, WHY? The news species is composed of the same chemicals as other lifeforms on earth: same nucleic acids, same amino acids, same lipids and so on. What are the chances that life evolved somewhere else in EXACTLY the same fashion as life here on earth?

What was different about this species was the genetic SEQUENCE (not the chemical composition of the hereditary material), which we would expect from a long time in isolation. No evidence for panspermia. Completely in line with standard evolutionary theory.

Life like ours must spread at some rate; the question is how fast. The faster it spreads the less likely any one place life is found is to be where that life started. This new datum favors the ability of our sort of to spread. Life similar to this could survive for a very long time in an asteroid or comet, living only on radioactive decay.

How to live off radioactive decay:

Saline ground waters in fractured crystalline rock at depths of 2-3 kilometers below in the surface in the Witwatersrand Basin of South Africa has been shown by IPTAI scientist to host microbial ecosystems sustained by hydrogen consumption linked to sulfate reduction. Sulfate and hydrogen in the Witwatersrand basin are continuously produced by water- rock reactions associated with radioactive decay of uranium. Radiolysis of groundwater water generates hydrogen as a primary product of disproportionation of water and generates sulfate as secondary product during reaction of hydrogen peroxide and pyrite. Based on data from sites in Canada, Finland and South Africa, deep groundwater in fractured rock represents a potential energy-rich environment for subsurface life and contains some of the highest levels of dissolved H2 ever measured in ground waters.

Hal, yes, it appears we have already seen ecosystems that can survive only on radioactive decay. So if enough of each species in such an ecosystem could survive in an asteroid or comet, life could survive. What is new here is a single species that can do it all, so you'd just need one of these little buggers to survive in an asteroid or comet for life to survive.

"Stars pass close enough to each other often enough as to swap some of their comet clouds, and reproduction would be needed to counter natural decay I think."

In deep space, even if the organism's metabolism is powered entirely by radioactive decay, the loss of heat would prevent metabolic activity and reproduction. Even with modern engineering, there's no power source capable of sustaining the kinds of temperatures necessary for reproduction for millions of years, short of a full-scale nuclear reactor (see http://en.wikipedia.org/wiki/Voyager_program#Powering_down).

Well, they don't "survive only on radioactive decay". The paper proposes that radiolysis acts on water and bicarbonate to provide some metabolic precursors that the bacteria need. But the precursors have to be there in abundance, and importantly, everything happens in an aqueous environment at 60°C. Their environment is wet and scalding hot - not what you find in a comet. Whether they could survive dormant in a deep-frozen piece of rock in interstellar space is an open question, of course -- but the data provided by the current study do not address that question. I don't think the odds on panspermia get an update with this discovery.

As an aside, the name Candidatus Desulforudis audaxviator is very interesting. The Candidatus is because it's never been seen - its existence is inferred from isolated DNA. Desulforudis refers to its metabolism. audaxviator, according to Wikipedia,

...comes of a quotation from Jules Verne's Journey to the Center of the Earth. The hero, Professor Lidenbrock, finds a secret inscription in Latin that reads: Descende, audax viator, et terrestre centrum attinges (Descend, bold traveller, and you will attain the center of the Earth).

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