One of the newest scientific specialties has as its subject the oldest living things: the unbelievably ancient fossils of the Pre-Cambrian period. Until very recently, the record of fossil life began with the Cambrian period, roughly 550 million years ago. But the fossils of that era were already complex, the remains of organisms far more advanced than the simple cells that scientists believed must have been the earliest living things. Were the more ancient forms too fragile to survive the fossilization process or had they simply gone unrecognized? As Darwin already recognized, the apparent absence of truly primitive forms in the fossil record might be counted an argument against evolution. One pioneer, J.T. Dawson of Canada, did use his claimed discovery of a "dawn animal" over 1.1 billion years old to raise questions about the missing links in the long stretch between it and the first Cambrian fossils. Dawson's claims were refuted, but other scientists took up the search. The strongest candidates were stromatolites, cabbage-like structures first identified in upstate New York in the 1870s. But their biological origin was controversial until the 1950s, when microscopic examination of fossil stromatolites, and the discovery of living stromatolites near Australia, clinched the case. Schopf, who as a graduate student contributed to the breakthrough, goes on to describe more recent research in the field—almost all of which has been done in the last 35 years. Now a professor of paleobiology at UCLA, he was part of the team that identified the oldest fossils thus far known: the 3,465-million-year-old Apex Chert microbes of Western Australia. Schopf combines his often entertaining personal story with an introduction to the discipline of paleobiology, with asides on the chemical makeup of life, questions still to be answered, and a skeptical look at the purported "fossils" from Mars. A good introduction to the history of a science on the cutting edge.
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