Evolution

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.

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.)

If most origin scientists would agree with Hazen that the beginning of life is probably both theoretically and experimentally discoverable, there isn’t much agreement on anything else about it. Contemporary debunkers of science — who include not just fundamentalist preachers but also Fox News commentators and much of the Republican Party’s leadership — like to depict scientists as a monolithic cabal of like-minded thinkers. As Hazen’s book makes clear, this is about the most singularly wrong-headed observation one could possibly make; origins research (like most scientific fields) is full of clashing egos, angry turf wars and full-throttle ideological collisions.

To simplify a complicated field slightly, Hazen frames origins research as consisting of three separate but interlinked scientific questions, each characterized by significant controversy. First comes the issue of where and how the first “biologically significant” organic molecules — the most basic building blocks of life — were formed. Next comes the murkier matter of how these basic sugars, amino acids and other primitive molecules were assembled into specialized “macromolecules,” which might be regarded as the missing link between non-life and life. Lastly, almost magically, these macromolecules organized themselves into ever more complex structures, capable of replicating themselves and passing genetic information along to their offspring. Somewhere along this continuum of intensifying complexity, life was born.

Even before addressing these questions individually, Hazen tackles one of the most exciting issues in contemporary cutting-edge science, which he argues provides an essential framework for thinking about the origin of life: the “missing law” of emergence. You may remember the second law of thermodynamics, from high-school physics or various “Star Trek” episodes: Energy has a ubiquitous tendency to dissipate from hot regions into cold ones; all natural systems decay from order into entropy. Hazen observes that this law is “more than a little depressing,” but goes on to the important — and, until recently, heretical — idea that “disorder is not the only end point in the universe.”

Much of what we find beautiful and valuable in the universe around us results from what scientists now call “complex emergent systems,” impressive ordered structures that arise, Hazen explains, when “energy flows through a collection of many interacting particles.” Such emergent phenomena occur all over the place in nature and in human society, on a vast intergalactic scale and a microscopic, molecular one.

What’s more, they cannot simply be understood as the sum of their individual parts. If scientists have not yet codified the law of emergence (and some might still dispute that it exists), Hazen sees it everywhere: “The arms of spiral galaxies, the rings of Saturn, hurricanes, rainbows, sand dunes, life, consciousness, cities and symphonies,” he argues, all reflect the tendency of such interactive systems to process energy into astonishing levels of complexity and order.

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“Genesis” is a book about science, not about philosophy or religion, but Hazen is precisely the sort of scientific Renaissance man who knows that the theoretical course he has set possesses teleological ramifications. If he weren’t such a clear and charming writer, it would be easy to find Hazen an irritating overachiever: He is not just an important researcher and a leading science educator, but also a professional trumpeter with the National Philharmonic and the Smithsonian Chamber Orchestra.

Some philosophers and theologians have seized on the proposed law of emergence to suggest, in opposition to the perceived nihilism of the natural sciences, that the purpose of our planet is in some sense the production of life, and the purpose of life the production of human consciousness (itself the most complex and elegant of emergent forms). Hazen avoids such metaphysical speculation, but unlike many scientists he is not hostile to those who would see God’s hand behind the entire process. In an aside about the “intelligent design” movement, he rejects its ticky-tacky technical arguments as inadequate not just scientifically but also theologically; he prefers a “God of natural laws” who “set the entire magnificent fabric of the universe into motion.” On several occasions he makes clear that he thinks that the basic requirements for life are “hard-wired into the fabric of the universe.” While such an argument certainly does not demand a deity, it’s also compatible with any non-fundamentalist variety of belief.

To turn from cosmology to specifics, the genesis of organic molecules on the primordial Earth is the best-understood of Hazen’s three questions — but what you may think you know about it is probably wrong. In 1953, a University of Chicago grad student named Stanley Miller scored a legendary experimental triumph by concocting a bench-top mixture of methane, ammonia, hydrogen and water — the presumed chemistry of the early oceans and atmosphere — and zapping it with electrodes to simulate lightning. In just a week of experiments, he produced an entire suite of amino acids and other organic molecules. The New York Times published a Page One story headlined “Life and a Glass Earth,” countless editorial cartoons depicted slimy critters crawling out of test tubes for their white-coated creators, and the myth of the primordial soup was born.

But Miller hadn’t created life, or anything close to it. As Hazen puts it, synthesizing a bunch of amino acids and then saying that you understand the beginning of life is like buying a pile of bricks and lumber at a supply yard and announcing that you’ve built a house. While the “Miller-Urey hypothesis,” arguing that life began in a rich stew of organics on the surface of the primordial ocean, has become a form of orthodoxy, it has all sorts of problems. Miller’s calculations about the composition of the Earth’s atmosphere were probably wrong. The harsh ultraviolet radiation at the surface of the ancient ocean makes it a most unlikely environment for those amino acids to join up and form proteins and other macromolecules. And finally, it has subsequently become clear that producing organic molecules is no big deal — the early Earth was probably covered with all kinds of organics, from many different sources.

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.

Has Platts solved this problem? Hazen would like to think so, but he’s far too cautious to say anything definitive. On a flight back to Washington after a scientific conference in Italy to commemorate the 50th anniversary of Stanley Miller’s experiment, Platts began to scribble ideas on his airplane ticket. It’s well known that much of the organic material from outer space to reach the prebiotic Earth came in the form of flat, sturdy molecules called polycyclic aromatic hydrocarbons, or PAHs. Platts began to see how PAHs could have been energized by solar radiation and self-assembled into stacks in the ancient ocean. Small, flat amino-acid molecules would begin to stick to the outside of this “stack of plates,” and the whole array would begin to look “for all the world like the information-rich genetic sequence of DNA or RNA.” This would have been nothing more than an intriguing, left-field notion if not for the fact that the space between these PAH layers is 0.34 billionths of a meter, which just happens to be precisely the distance between the ladder-like rungs of a DNA or RNA molecule. Somehow — and Platts doesn’t propose exactly how — this interesting but haphazard assemblage of molecules became a coherent vector of biochemical information, broke free of its PAH host and folded over on itself to become a “true pre-RNA genetic molecule.”

If this isn’t how life began, Hazen argues, then it’s probably the kind of guess that moves us in the right direction. In the end, he suspects that the dichotomy between metabolism and genetics is as misleading as that between life and non-life. Hazen admires the chemical plausibility and conceptual simplicity of Platts’ hypothesis, but more important, it points toward the possibility that a crude genetic molecule and a crude metabolic cycle could have developed jointly, with evolution rapidly favoring those molecules that protected their genetic code better and metabolized more efficiently. On Platts’ primordial earth, one could argue, every scientist gets a piece of the action, and none of the hypotheses propounded (“clay life” perhaps excepted) is completely wrong.

What makes Hazen’s scientific cum philosophical theorizing so appetizing, especially to humanities-based readers like myself, is his refusal of dogmatic opposition and his desire to encompass apparently opposing positions. Along with his wholehearted embrace of emergence, with its faintly squishy odor, this may not endear him to hard-science types less eager to leaven the biochemistry lecture with God or Napa Valley cabernet or scientific sexism or Chaucer or the other peripheral issues Hazen drags in from time to time. Like most readers of this book, I don’t have any real idea whether Hazen is right that life is emerging all around us, in a faintly deistic universe pregnant with immanent possibility. But given the time and place of this book’s publication, it sure is nice to think so.