The Cradle of Life

Fossils, Fallacies, Foibles, and Fantasies: The Cradle of Life

by J. William Schopf

Princeton University Press, 1999, 359 p.
ISBN 0-691-00230-4, $29.95 U.S.

"Though all the winds of doctrine were let loose to play upon the earth, so Truth be in the field."
-- John Milton, Aeropagitica

An advocate of deep-sea exploration and the protection of the marine environment was once quoted as asserting that we know more about the far side of the Moon than the bottom of the oceans. Paleontologists might claim with equal rigor that we know less about life on the Precambrian Earth than the seafloor: The fossil record of organisms visible to the unaided eye dwindles in the geologic record older than 545 million years ago and essentially vanishes in rocks only slightly more ancient. This Cheshire Cat behavior of the fossil record, a source of consternation of Charles Darwin, serves as the intellectual instigation for William Schopf's account of the dawning of the field of Precambrian paleobiology and his contribution as the co-discoverer of the oldest known fossils in the 3.5 billion year-old Apex rock formations of Australia. The twin themes are a scientific one; that life in the Precambrian, and particularly in the Archean eon (prior to 2.5 billion years ago) was almost exclusively microbiological, leaving commensurately micron-sized (read, difficult to find!) fossils; and a psychological one; that science is a human effort, and that in the interpretation of the fossil record our human imaginings, fears, schemes, and biases come into play. Schopf, whose meticulous work discovering ancient microbial fossils has helped extend our vision of life on Earth into the "deep time" of the Precambrian, tirelessly advocates the same care in the search for life on Mars.

The book reads more like a collection of essays rather than a seamless treatise, and I actually found the material more accessible as a result. With some exceptional cross-referencing, the chapters or groups of chapters could be read in a different desired orders. The style, too, makes for comfortable reading and Schopf's frequent exhortations (among them the liberal use of the exclamation point) convey his excitement about the field to the reader. In one chapter, he laments the delayed discovery that most stromatolite fossils are the remains of microbial mats – communities of microorganisms -- and attributes it to a lack of communication between the disciplines of the life and physical sciences. Schopf ably demonstrates his own interdisciplinary ability in this engaging book as he discusses topics ranging from the history of the discovery of Precambrian microfossils, theories on the origin of life, the evolution of metabolism, and the rise of eukaryotic, oxygen-respiring cells.

I personally enjoyed his description of the strategy for looking for very old rocks, for fossiliferous deposits within those formations, and for identifying candidate fossils within those deposits. His elaboration of the five criteria for determining bona fide ancient microfossils will be invaluable for those whose aspirations include searching for life on early Earth or Mars. His chapter on stromatolites is also well done, including his careful definition and description of how these fascinating formations form and bring us information about ancient microbial ecologies across billions of years of Earth history. Shopf shines in his enthusiasm and excitement, and there are rewarding instances of prose such as his analogy to the evolution of successive metabolic pathways as arising "like the ramparts of a medieval city…" The photographs of the fossils and geologic units are stunning, and it is unfortunate that they do not play a more central role in the book.

The manuscript could have withstood improvement in both style and accuracy. Schopf seems to be unsure of his audience, as the book hovers uncomfortably in a twilight zone between the educated layman, who can follow the logic but does not have the background to fill in the details, and the colleague in the field, who can supply the "missing mass" but who may find the logic overly simplistic. Another weakness of the book is the disconnect between the text and the figures and lack of identification of the sources of data. There is also a persistent background level of scientific inaccuracies or mistakes that, while not fatal, are just sufficient to be annoying. Examples include the use of "tiny bar magnets" as an analogy to the electric dipole of a water molecule, the use of "autotrophy" vs. "heterotrophy" in a more generalized way than the standard definition of carbon source, and the suggestion that a 5 km impactor could have boiled the away the world's oceans – planetary scientists typically quote a diameter closer to 200 km. Molecular microbiologists might disagree with the assertion that 3-5 times as many unknown species exist as are known; estimates of the fraction of bacterial species which remain uncultured (and thus uncharacterized) is 99-99.9%! There are also many instances where some facet of evolution is explained as though the theory were fact and not hypothesis and insufficient background information is given. Among these are the timing of the molecular machinery of life and its encapsulating micelle or membrane, the evolution of ferrodoxins (apparently based on the 1966 paper by Eck & Dayhoff), and the meaning of the absence of mitochondria in deep branching, "primitive" eukaryotes (some of which do turn out to have mitochondrial heat-shock proteins). Personal cultural digressions (a visit to Salvador Dali in Spain and a tour of a commercial stromatolite warehouse in China), while interesting in their own right, probably will only serve to distract the reader.

Schopf is at his peak in the final two chapters when he relates two (now, almost apocryphal) tales of fossil misinterpretation from the 17^th and 18^th centuries and suggests (barely implicitly) a modern version – the claims that there is chemical and physical evidence of past organisms in Allan Hills 84001, the meteorite from Mars. Schopf's vision of the human side of paleontology includes very human scientists that convince themselves of an erroneous interpretation of the fossil record either to satisfy the "politically correct" status quo or to achieve the noble but self-gratifying goal of a breakthrough in human knowledge. These are relevant issues in the new media era of sound bites and science press conferences, of sophisticated models and simulations which blur our perception of what the evidence allows, i.e., what may have happened in the past, and what the evidence proves, versus what actually happened. Schopf's exhortations for careful work in the book make for important reading. I would have complemented this picture with anecdotes of scientists who did propose visionary but controversial theories against the "prevailing wisdom" and were later proven to be correct (the theory of plate tectonics comes to mind). Science advances not only by the many who incrementally advance our firm understanding of the facts, but also by a few who dare venture to the edge of our knowledge and suggest things that may be waiting to be discovered. The important thing, as Schopf reminds us in so many words, is to distinguish between the two.