Stanley Miller, of the famed Urey-Miller experiment, died Sunday (NYTimes Obit).
Here's an entry from over a year ago that was catalyzed by a conversation with a former member of the Miller lab:
Last night, my wife and I had dinner with a friend of ours from the Szostak Lab (yes at Buddha's Delight - I had the "beef" taro stirfry).
There we discussed Capote (we just saw the movie) and the existence of ribose in a pre-biotic earth. Apparently it is unlikely that sugars, such as ribose, would have been in high concentrations in the hypothetical chemistry of primitive earth (see her PNAS paper). Although sugars are easily generated (spontaneously from formaldehyde), they decay very rapidly - thus at steady state it's likely that there wasn't much sugar around. Sugars form the backbone for molecules such as RNA and DNA.
No sugars, no ribose based nucleic acids.
Thus a self-replicating molecule would probably require a different backbone, perhaps one composed of polypeptides. Such peptide nucleic acids (or PNAs) have been synthesized in labs and have interesting properties, such as the ability to hybridize with single stranded DNA.
So this morning I got up with thoughts of tofu beef, effeminate NY intellectuals, and the origin of life, swimming through my head ... as I opened up the paper and read, Saturn Moon Has Geysers, Hinting Life Is a Possibility.
(Image from NASA - for more see the special edition of Science Magazine by following this link.)
So Cassini found evidence of liquid water on Enceladus ... very interesting. Then (in the NY Times article) I read this sentence:
Life requires at least three ingredients -- water, heat and carbon-based molecules
No no no. You don't know that life requires water! This is a good example of pretending to know more than we do. Perhaps life can arise in another medium - how do we know? For a complete discussion on this topic, I have an old post discussing the relationship between life and water.
My point. Compare this rash absolutist idea (life NEEDS water), to a careful study with a conclusion (in the probable chemistry of pre-biotic earth, self-replicating molecules MOST LIKELY did not contain sugars). These are examples of bad and good reasoning with regards to the origin of life.
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Thank you! This has long been a pet peeve of mine. I always mentally insert "as we know it" between "Life" and "requires" whenever I read this sort of thing.
A physicist friend of mine (Chris Crawford, the game designer) takes a thermodynamic approach to the question. He argues that the foundational element life really needs is simply a strong negative-entropy gradient, which allows natural systems -- energy engines, so to speak -- to develop that organize within that gradient. At which point Darwinian selection starts to set in, and proto-life begins to appear.
He one time posited, as an intellectual exercise, how electromagnetic lifeforms might form in the outer layers of a star's photosphere. Cool idea, eh?