- Gen·e·sis: The Scientific Quest for Life’s Origin
- Joseph Henry Press, 339 pp.
More Questions Than Answers
In all the recent noise over the higher steps of evolution and the proper way to teach them in American schools, it’s easy to forget that science hasn’t established the first big step: how the basic building blocks of life—the nucleotides that make up Watson and Crick’s celebrated reverse spiral staircase—organized into life proper. Even those of us who accept that DNA and Darwinian evolution are the only game in town must acknowledge the huge gaps in scientific theory at critical points in the story of life on Earth.
Over the past few decades of public and sometimes legal debates concerning creationism and intelligent design, chemists, biochemists, marine biologists, and even mineralogists have quietly pursued the question of how proteins organized into self-replicating cell structures.
Gen·e·sis, the latest book to give us a comprehensive snapshot of “where we are” comes from a seemingly unlikely source: an earth scientist trained in mineralogy and crystallography. Trained at MIT and Harvard, Robert Hazen does research in the Geophysical Laboratory at the Carnegie Institution of Washington and is also Clarence Robinson Professor of Earth Science at George Mason University. Hazen has authored 16 previous books, including The Breakthrough, Why Aren’t Black Holes Black, and Science Matters: Achieving Scientific Literacy, co-authored with James Trefil. (He’s also a professional trumpeter with the Washington Chamber Orchestra, the National Gallery Orchestra, and the Smithsonian Chamber Orchestra, but that doesn’t really come up in this otherwise wide-ranging book.)
Hazen gives a broad overview of the players, issues, theories, and significant experiments involved in origins research over the past few decades. If mineralogy strikes the reader as an unlikely discipline for a scientist pursuing questions of the origin of life, then that reader hasn’t been keeping up with developments in the field. We’ve long known (or believed) that fire and water reacted with gases to create at least the potential for life, but what if rocks turned out to have played an integral role in the process? That possibility has reared its intriguing head in the past 20 years.
It was only a few years after Watson and Crick established the existence and structure of DNA that Stanley Miller and Harold Urey showed how simple amino acids could be produced by shooting electricity into a “primordial soup” such as might have covered the Earth in its earliest days: methane, ammonia, hydrogen, and water. We all learned about this much celebrated experiment in high school biology; the problem has been how things might have progressed from there.
On closer examination, the Miller-Urey lightning-in-the-soup scenario raised too many unanswered questions. For one thing, though a range of simple amino acids, hydrocarbons, carbohydrates, and metabolic acids were easily produced by lightning-in-the-soup (and, in subsequent experiments, in ice), others never showed. For another, Miller and Urey could not explain how the small molecules their experiment did create managed to combine into the much larger molecules that make up proteins, or begin their complex dance with enzymes that is so much a part of life as we know it. Also, ultraviolet radiation, of which there was probably plenty in early times, tends to split large molecules, not make them.
Data and calculations based on the composition of ancient rocks have suggested the early terrestrial atmosphere was not composed of the particular soup Miller and Urey chose, but a much less friendly mix of carbon dioxide and nitrogen. Additionally, the process by which most cells gain energy—splitting a six-carbon sugar, glucose, into two energy-rich pyruvates (three-carbon molecules) and then smaller structures—just doesn’t work very well at room pressure. Perhaps Miller-Urey’s wonderful zap of life will turn out to have been a dead end.
Subsequent potential breakthroughs received much press coverage. In the late 1970s the discovery of new life forms near hydrothermal vents—volcanic hot spots a mile and a half beneath the ocean—showed that life did not require sunlight to exist, but posed its own challenge for origins research: some steps in the assembling of carbon-based molecules don’t work well in water. And the heat from such vents could easily be too extreme to build and sustain macromolecules as well as many forms of life, especially oxygen-based, sun-loving versions.
Could terrestrial life have originated in outer space? Not from Van Daniken’s astronauts but from organic matter brought by meteors? Organic molecules such as carbon-based compounds, and tiny sausage-shaped objects that resemble bacteria, were found on an Antarctic meteorite whose mineral composition strongly suggested it had come from Mars. This made big headlines in 1996, but again there were too many unanswered questions, not the least of which was whether the “signs of life” were nothing more than post-impact contamination.
The above gives some sense of the challenges and questions that face origins research. There are many others, and Hazen carefully delineates them: Did life begin when the first semi-permeable membrane made cells possible, or as a metabolic cycle without cells, or when some RNA-like genetic transfer system first developed? How did hydrocarbon chains (the lipids that make up cell membranes) enter the picture and thereby protect life’s carbon-based constituents from dissolving in water, which they so easily do? Is it possible that early forms of life were nothing like what we see on Earth today, and that various forms—like a branch or two of the early genus homo—were unsuccessful, outmoded, superseded by later varieties? Is a “top-down” approach (examination of all existing and fossil life forms on Earth in order to extrapolate back to the beginning) or a “bottom-up” one (trying to mimic emergent chemistry from scratch in the laboratory) more likely to come up with the answer?
To cut to the chase where this author is concerned, perhaps the two questions that most guided Hazen and his colleagues are: Given that many forms of macromolecules seem to require high pressures and temperatures to synthesize (yet so easily break down in the presence of extreme heat, as well), what scenario would have provided such conditions? Secondly, given that it’s very difficult for larger organic molecules to construct themselves when exposed to air, water, low or very high heat, radiation, and so many other irritations, what might have provided assistance—a lattice, if you will—as well as the necessary energy boost for such molecules to come into existence?
Could it have been minerals deep in the earth or at the bottom of the oceans? The short answer is that it could. Certain minerals could have provided the energy to promote key chemical reactions, protect proto-macromolecules from extremes of heat, and offer a low-tech framework—a lattice—to which organic molecules might adhere. This would enable them to mirror or mimic the structure of minerals and thus build large organic molecules.
For those who have been unaware of recent theoretical developments, Hazen provides a handy introduction to the personalities and work of such scientists as Tullis Onstott (whose teams have found microbes in water samples from South African gold mines as deep as two miles underground, where sunshine has never pierced), Thomas Gold (who argues that petroleum is a renewable resource that comes from chemical processes deep in the earth, not a fossil fuel from sediments near the surface), Jennifer Blank (whose forty-foot experimental gas gun fires stainless-steel capsules containing amino acids and water at rock, and shows that while some are destroyed, some combine), Christopher Dobson (who posits “aerosol life,” in which tiny droplets sprayed from ancient oceans, floated, collected dust, and enabled lipids to form spherical membranes), and especially Günter Wächterhäuser (a patent attorney trained in chemistry who has propounded a sweeping theory of early evolution based on the muscular participation of iron and nickel sulfides).
Hazen’s book gets a little technical at times, as it probably must, but not for long. There’s never a point where the general reader will inevitably feel the discussion has gotten irrevocably away from him, even if it gets a little abstruse about molecular structures and biochemical processes for, say, five or ten pages. Hazen readily pulls back and moves on to introduce other scientists and theories, because there are still so many entries to origins research, so many potential directions from which to attack the questions. (In fact, at one point, he grants: “In spite of the polarizing advocacy of one favored environment or another by this group and that, experiments increasingly point to the possibility that there was no single dominant source” of life on Earth.
There’s a bit of humor when pet theories clash and scientists turn petty and defensive. “Organics from outer space, that’s garbage, it really is,” Miller says of meteorite scenarios. “There’s probably nothing there, because, otherwise, people would have found it already,” another says of Wächterhäuser’s theories.
Hazen provides another form of relief now and then when his book steps completely out of its primary narrative to indulge in what the author calls an “Interlude” of two or three pages. This can vary from a swift disposal of “intelligent design” (“Why do we have to invoke God every time we don’t have a complete scientific explanation?”) and a discussion of scientific mythos versus logos (“Who’s to say you’re not just writing another creation myth?” his wife teases him) to the slightly more mundane (but still important) question of why there are so few women scientists in this saga.
A final plus is that Hazen is an excellent writer. Clear, direct, friendly, and occasionally philosophical or poetical, he makes an excellent guide through some difficult and arcane thickets of scientific inquiry:
The art of science isn’t necessarily to avoid mistakes: Rather, progress is often made by making mistakes as fast as possible, while avoiding making the same mistake twice.
Most of the atoms in your body were once part of mastodons, dinosaurs, trilobites, even the earliest living cells. Take a moment to look at the palm of your hand and imagine the fantastic yet unknowable histories of its countless trillions of atoms. Earth’s biosphere is the ultimate recycling machine.
So why give this fine book “only” three and a half stars? It’s a tough call, because the writing quality — particularly for a science text by a working scientist — is worth at least four, and the subject of enduring interest. Perhaps the subject is not of burning interest to general readers, however, and the fact that this particular detective story ends inconclusively may inevitably disappoint. So be advised that origins research as depicted in this book is very much a “work in progress,” and recognize that if you are not deeply interested in the topic in any case, Gen·e·sis may not be as rewarding to you as a more retrospective scientific work, or a good novel.