Fossils are the remains of plants or animals or the physical records of their presence in prehistoric times. The definition also includes early man-made tools and human remains that greatly predate written records. The study of fossils is called paleontology. One who studies fossils is a paleontologist.

In a pragmatic society, the question "Why should we study this?" is often asked. The study of paleontology offers many answers:

  1. Organic evolution - Sedimentary rock documents the occurrence of life on earth from the simpler organisms to the most complex plants and animals. Of course, the record is incomplete. But with what there is, the student can trace much of the evolution of life on earth. A dramatic example of this is the fossil of the extinct Archaeopteryx, the so-called "link" between reptiles an d birds. Without this fossil and the discovery of many new types of feathered reptiles and early birds from China, the conclusion that birds evolved from reptiles would be a great deal more questionable.

  2. Biostratigraphy - Fossils aid the paleontologist in dating rock. All species of animals and plants lived only during certain intervals of time. This time interval is bracketed by their earliest appearance as a result of their evolution and their last occurrence just prior to their extinction. Consequently, fossil remains will position the rocks in which they are found in a sequence from oldest to youngest. This is especially important in oil drilling, as certain fossils are the keys to the age of specific subsurface rock formations, some of which are know to be oil-bearing. The use of fossils in relative time dating is called biostratigraphy.

  3. Geochronology - Fossils can sometimes be dated in an absolute sense, that is, in terms of an actual age in years. Absolute age dating, or geochronology, includes the carbon-dating of relatively young (up to 50,000 years ago) wood or the dating of radioactive minerals found with older fossils. Once a relatively old fossil is dated at one locality, the presence of this same fossil can be used to approximate the age of the enclosing rock at other places.

  4. Environment - Modern and ancient organisms are limited to specific habitats. Ancient environments can be reconstructed by studying features preserved in the rocks and by comparing them with features known in modern sediments and modern environments. For example, rocks that preserve root horizons, ancient soil horizons, and stream deposits were laid down on land. It is also known that much of the inland United States was covered several times by shallow seas over the last 500 million years. This is proven by the evidence of marine fossils in these rocks. It can also be shown that the present north and south poles were once warm by pointing to fossilized tropical swamp plants that are now found in polar rocks.

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