Weird science

Hazen himself is something of a "ventist," a member of the small cadre of scientists who suspect that hydrothermal vents on the ocean floor -- where boiling geysers meet cold ocean water, catalyzing a complicated stew of mineral decomposition and chemical reaction -- might have been the cradle of life. More than a mile beneath the sea's surface, in total darkness, these seemingly hostile environments actually host vibrant ecosystems, and provide a potent, consistent supply of nutrients and energy. As one of the oceanographers who discovered such vents in 1977 observed, they could have been "ideal reactors for abiotic synthesis." Stanley Miller considered the vent hypothesis "a real loser," as he once told a reporter for Discover magazine, adding, "I don't understand why we even have to discuss it." But microbial life has now been discovered in all sorts of deep, hot environments: Below South African gold mines, in rock cores drilled for oil wells, nearly seven kilometers deep in a 368-million-year-old mass of Swedish granite. Hazen introduces us to Tommy Gold, a maverick Cornell astrophysicist who argues that petroleum is not the fossilized and inherently finite remains of ancient life forms but rather an endlessly renewable byproduct of the microbial life that thrives below us by the zillions. (The fact that oil companies have not lavished funding on Gold suggests that their geologists are skeptical of this idea.)

If the vent theory remains controversial, it has thrown open the doors to countless other ideas. One of Hazen's heroes is German patent attorney Gunter Wachtershauser, who moonlights as an eclectic chemistry researcher and has published a sweeping rejection of Miller's ideas, arguing that early life was an emergent process that relied on energy drawn from iron-sulfur minerals in rocks, either deep underwater or deep in the Earth, and not from lightning or the Sun. NASA astrochemist Louis Allamandola has concluded that ice-covered dust molecules in deep space, bombarded by ultraviolet radiation, become a constant source of primitive organic material, which reaches Earth -- and every other planetary body -- in comets, asteroids, meteors and just floating cosmic dust. (Stanley Miller doesn't like this one either, telling the Discover reporter: "Organics from outer space, that's garbage, it really is.")

One could go on. Another NASA scientist, Friedemann Freund, has argued that organic molecules are released by the erosion of igneous rock, and despite one mineralogist's assertion that this is "utter nonsense," this idea too remains experimentally in play. But the bottom line, as Hazen puts it, "is that the prebiotic Earth had an embarrassment of organic riches derived from many likely sources. Carbon-rich molecules emerge from every conceivable environment." Stanley Miller didn't discover how life began; he only discovered that creating organic molecules out of basic chemical ingredients was the easy part.

It probably helps to know some basic biology and chemistry as you follow Hazen through his discussion of questions two and three -- the assemblage of primitive organic molecules into "biologically significant" macromolecules, and the subsequent emergence of self-replicating organisms -- which are necessarily more technical. Still, he's an educator by instinct as well as training, and I never felt condescended to by his explanations. Before long you'll find yourself nodding in agreement as he outlines the differences between prokaryotes and eukaryotes, or details the role amphiphilic lipids -- fat molecules that seek water at one end, and reject it at the other -- played in the formation of primitive cell membranes.

Hazen's own research (conducted with chemist Glenn Goodfriend, whose untimely death Hazen documents movingly) points toward the idea that chemical reactions of the sort found in deep, hot environments led inexorably to the development of ever more complex macromolecules, and that the surfaces of mineral crystals played a key role in their self-organization. Critics might respond that Hazen is both a mineralogist and a ventist, and so predisposed to believe such things, and there's no question that the development of "proto-life" at the molecular level remains a murky area that offers more speculation than hard data.

Did "lipid vesicles" -- the ancestors of modern cells -- first appear in space, in the ocean or in the atmosphere? Did minerals like clays and hydroxides polymerize long molecular chains and strands of primitive RNA? Does life's strong tendency to prefer "left-handed" amino acid molecules and "right-handed" sugar molecules signify that the creation of life, defined as "the self-organization of molecules into a replicating entity," was a singular event that occurred just once in a particular environment? There are no definitive answers to any of these questions, but Hazen's elucidation of the state of contemporary research makes clear that it's the interaction of biology, chemistry and geology, and not any of those disciplines alone, that can clarify them.

Nick Platts, the graduate student who wound up in Hazen's office that day in May 2004, believed he had found the answer to the third question. You can't answer that one, as Hazen explains, without staking a position on the most intractable debate in origin science. The two essential processes in cellular biology are metabolism and genetics -- the organism's ability to nourish itself from its environment, and its ability to pass on biological information to future generations. But most scientists believe one of these processes had to come first. Which was it?

As a disciple of emergence theory, Hazen looks to the "chemical simplicity of primitive metabolism" as the core process that defines the beginning of life. Chemists, physicists and geologists, he writes, tend toward this metabolism-first view, while biologists, "dominated by the powerful, unifying spell of the genetic code," see it the other way. Wachtershauser envisions an "iron-sulfur world" where colonies of non-cellular "flat life" -- which would be invisible even to modern scientific instruments -- existed (and may still exist) on grains of sulfide minerals. They possessed nothing we would now recognize as genetic material, but thrived and spread based on a simple process of chemical reaction called the reverse citric acid cycle. It's not a terribly sexy picture of our earliest ancestor, and Hazen isn't even sure you can call such a self-replicating chemical film alive.

Biologists like Leslie Orgel of the Salk Institute or Jack Szostak of Harvard have focused on the evolution of a self-replicating genetic apparatus -- probably the nucleic-acid molecule RNA, now believed to be a precursor to modern DNA -- as the true beginning of life. RNA seems to be a tremendously diverse and ancient biomolecule, capable of both carrying genetic information (as DNA now does) and catalyzing all kinds of interesting biochemical reactions. Szostak has actually predicted that he will soon create a synthetic life form in his lab, presumably a self-replicating strand of RNA enclosed in a lipid membrane.

Even if Szostak succeeds in cooking up a Frankensteinian glob of gene-bearing goo -- a process that may cause science more problems than it needs -- Hazen doesn't believe that life on Earth actually began that way. He views the Orgel-Szostak "RNA World" as "a critical, but relatively late, transitional stage that occurred when life was well established." This is where seemingly loony ideas like Cairns-Smith's "Clay World" come in -- somebody's got to come up with a mechanism that bridges the gap between a planet covered with a random stew of interesting molecules and the incredible complexity of RNA.

Next page: So, did that graduate student actually discover how life began?