(c) Anthony K. Grafton 2003

Fascinating Fossils

Most people need look no further than the nearest gravel road or driveway for evidence of life from millions of years ago. We often call such evidence “fossils”, but this is a word that can mean many different things.

Petrified fossils are the remains of living creatures that have had all the small pores and openings filled with precipitated minerals. Petrified wood is a commonly found example of such a fossil. But the skeletons of dinosaurs and other ancient creatures shown in museums are called replacementfossils, meaning that every part has been replaced by minerals and rock, leaving no original material like in petrified fossils.

Another common kind of fossil is called a mold. Molds can be formed when remains are buried in sediment that turns to rock over many centuries. If the organic remains are dissolved away, the remaining hollow space in the rock, shaped like the original organism, is called a mold. Molds give information only about the outward appearance of the buried animal or plant.

There are many other kinds of fossils, including animal tracks or burrows, coprolites (fossilized animal dung), and gastroliths(polished stones used in the digestive systems of some ancient animals) just to name a few. But all fossils have two things in common: they are usually hundreds of thousands or millions of years old, and they are the only way we can study the variety of life that inhabited the earth long before man.

Have you found an interesting fossil? Mail a picture of yourself and a close-up of the fossil to Science Corner, and perhaps your find can be featured in a future column!