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Sunday, Jul 12, 2009
Are we descendants of clay? Is rock slime related to Grandpa? A fantastic new book tours the competing theories of how life on Earth began 4 billion years ago.
Oct 31, 2005 | In May of 2004, Robert Hazen got to have one of those moments that occur more often to scientists in movies than those in the real world of labs, conferences, grant applications and endless, tedious experiments. Hazen is a geologist and mineralogist who divides his time between the Carnegie Institution of Washington and George Mason University, and one Thursday afternoon that May, an Australian graduate student named Nick Platts came into his Carnegie office. Platts was pushing 40 and trying to complete a mid-career switch from high-school teacher to research chemist; his dissertation seemed to be going nowhere, and he was in danger of being deported back Down Under.
"You got a few minutes?" asked Platts. Hazen said yes, expecting an excuse-laden update on the progress of Platts' thesis research. Instead, Platts sat down and said, "I've found something extraordinary. I think I've discovered how life began."
This is the crowning anecdote in Hazen's mesmerizing "Genesis," an account of the exciting and often eccentric quest for answers to the great conundrum on the outermost frontier of the earth sciences. How did a lifeless planet of rocks, water and atmospheric gases give birth to all of this -- to microbes, lichens, redwoods, hippopotamuses, starfish, you and me? OK, the Darwinian theory of evolution suggests that you and I and the hippos and all the rest were almost Calvinistically preordained once life (whatever that is exactly) got started in the first place. But how in hell did that happen? Despite a lot of mumbling about the "primordial soup" of the ancient oceans, scientists until recently haven't had much of a clue.
Some scientists maintained, in fact, that the question of "abiogenesis" -- how life arose from non-life, something like 4 billion years ago -- was pretty much unanswerable and unknowable. Presumably, some chain of unlikely chemical reactions on that world of rock and water had stuck organic molecules together into primitive microoorganisms that began to reproduce and evolve. But the evidence of exactly what happened and how was destroyed long ago, and no conceivable regimen of laboratory experimentation could reproduce such a fluky sequence of events.
"Genesis: The Scientific Quest for Life's Origins"
By Robert M. Hazen
Joseph Henry Press
339 pages
Nonfiction
Hazen belongs to the growing chorus of scientists who reject this view, and argue that life wasn't a fluke at all. Many of them believe instead that life is an "emergent form," a self-perpetuating cycle of increasing complexity that may occur inexorably, given the right combination of water, chemicals and energy. As the polymath Hazen is well aware, the scientific ramifications of this idea are enormous, and are liable to leak out into philosophy and even theology. If life can appear as an orderly chemical sequence in all sorts of environments, it is almost certainly not limited to Earth alone. It may well be found on Mars; on Jupiter's moon Europa, with its miles-deep oceans; Saturn's moon Titan, with its rich atmosphere; and countless other places in the universe.
Furthermore, Hazen and other like-minded scientists insist they are not searching for some singular, miraculous occurrence that brought life out of nothingness, as God does in the Old Testament book that lends Hazen's volume its name. There is no absolute dichotomy between life and nonlife, Hazen tells us; the transformation from "a prebiotic Earth enriched in organic molecules" to anything your high school biology teacher would recognize as modern cellular life did not occur in a single stroke. Rather, it was a "progressive hierarchy of emergent steps": Different kinds of molecules were synthesized and concentrated, then began to cluster together in various systems, which in turn began to replicate themselves and at some stage became encapsulated within cellular membranes.
"To define the exact point at which such a system of gradually increasing complexity becomes 'alive,'" Hazen writes, "is intrinsically arbitrary." Is a living thing an isolated entity? Then life begins with the first enclosed cells. Is life defined by its ability to reproduce? Then the first self-replicating clumps of molecular goo were alive. Does life mean the passing of genetic information from one generation to the next? Then it begins at a different point, with some primitive ancestral form of DNA or its precursor, RNA. As a mineralogist, Hazen admits to a fondness for the notion that the first life form was a microscopically thin layer of molecular slime attached to rock surfaces, which spread lichen-like from one to the next. Look, it's Grandpa!
That vision of life's beginning isn't so strange, relatively speaking. In Hazen's delightful guided tour of the wild theories, daring experiments and raging feuds that have made many scientific institutions view origins-of-life research as a fringe field, we encounter lots of unlikelier notions than living rock gunk. One perfectly respectable scientist, Scottish chemist Graham Cairns-Smith, actually argues that the first life on Earth might have been inorganic -- in fact, that it might have been clay crystals, which he suggests both grow and pass on a form of "genetic information" through their "mutable layered structure." That's right: He thinks clay is alive.
Hazen doesn't even find it necessary to bring up the eerie biblical resonance of this idea. (So when the prophet Isaiah proclaims to the Lord: "We are the clay, and thou our potter," no metaphorical reading is required!) But his great strength as a scientific communicator, that rarest of species, is his simultaneous honesty and open-mindedness. Hazen makes clear that he doesn't find Cairns-Smith's theory -- roughly, that the self-replicating inorganic clays formed a sort of scaffolding or template for the creation of organic life -- entirely convincing, but at the same time he is thrilled by its sweep and ingenuity, and delighted to report that it has yet to be proved wrong. (Indeed, given the difficulty of propagating and observing "clay life" in the laboratory, it may never be.)
