Fossils are the remains or traces of ancient organisms, preserved over the ages in rock, amber, tar, ice, or another medium. Scientists who study fossils, called paleontologists, use a variety of techniques to reveal what an ancient organism looked like, where it lived, what it ate, and how it behaved.

Today, we take for granted that a fossilized tooth or bone came from a creature that lived long ago. But that wasn’t always true. In the 1600s, as fossils began to be systematically studied, there was vigorous debate about how to interpret them. Some argued they were not remnants of living things. This was because fossils were made of stone—the same kind of stone as the surrounding rocks, not bone or tooth or shell—and because there was no known mechanism for how they could be buried so deeply within the earth. Furthermore, fossils frequently did not resemble any living creature, and at that time it was widely believed that species were “fixed,” or unchanged since their creation. Extinction was not believed possible. By the late 1600s, however, arguments that fossils are in fact the hardened remnants of past life began to win the day. Devout Christians such as John Ray and William Smith played an important role in describing and understanding the true nature and distribution of fossils. These early Christian geologists saw God as creator of these life forms that lived in distant ages past.

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