Bones, teeth, shells, and wood can be buried and remain chemically unchanged for millions of years. Most Miocene, Eocene, and Pleistocene shells such as those found in Maryland, Virginia, Florida, and California are essentially the same as when they were buried. Often the only clue to tell these 20-million-year-old shells from their modern counterparts is loss of color and luster. Many bones dredged up in midwestern gravel pits are little changed since they once held together ice-age animals.
One location in Tennessee produces 135-million-year-old Cretaceous shells of remarkably modern appearance, even to the pearly luster. Sometimes the original aragonite of the shells has changed to calcite, chemically the same but different in crystal structure. Logs embedded in Eocene coal deposits often resemble a modern-day fireplace log and are quite capable of being burned.
Relatively recent fossils of animals preserving flesh, skin, and hair have been dredged from peat bogs, where tannic acid in the water has saved them from decay. The body of a man so fossilized rests in the science museum in Copenhagen, Denmark, his face clearly showing a three-day stubble of beard. In Galicia, now part of the Soviet Union, a rhinoceros carcass was found pickled in an oil seep.
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