Written In The Rocks

The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.

—Charles Darwin, On the Origin of Species

The story of life on Earth is written in the rocks. True, this is a history book torn and twisted, with remnants of pages scattered about, but it is there, and significant portions are still legible. Paleontologists have worked tirelessly to piece together the tangible historical evidence for evolution: the fossil record.

When we admire breathtaking fossils such as the great dinosaur skeletons that grace our natural history museums, it is easy to forget just how much effort has gone into discovering, extracting, preparing, and describing them. Time-consuming, expensive, and risky expeditions to remote and inhospitable corners of the world are often involved. My Chicago colleague Paul Sereno, for instance, studies African dinosaurs, and many of the most interesting fossils lie smack in the middle of the Sahara Desert. He and his colleagues have braved political troubles, bandits, disease, and of course the rigors of the desert itself to discover remarkable new species such as Afrovenator abakensis and Jobaria tiguidensis, specimens that have helped rewrite the story of dinosaur evolution.

Such discoveries involve true dedication to science, many years of painstaking work, persistence, and courage—as well as a healthy dose of luck. But many paleontologists would risk their lives for finds like these. To biologists, fossils are as valuable as gold dust. Without them, we'd have only a sketchy outline of evolution. All we could do would be to study living species and try to infer evolutionary relationships through similarities in form, development, and DNA sequence. We would know, for example, that mammals are more closely related to reptiles than to amphibians. But we wouldn't know what their common ancestors looked like. We'd have no inkling of giant dinosaurs, some as large as trucks, or of our early australopithecine ancestors, small-brained but walking erect. Much of what we'd like to know about evolution would remain a mystery. Fortunately, advances in physics, geology, and biochemistry, along with the daring and persistence of scientists throughout the world, have provided these precious insights into the past.

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