Fossils: A Link to the Past

By Diana Dell

Fossils are the remains or records of ancient living things. Fossils may be a whole animal preserved in ice, a bone or tooth hardened by minerals, an insect encased in amber, a footprint, or the outline of a leaf.

The remains of most organisms decay or are consumed by other animals. However, if the body sinks into muddy riverbeds, or a tar pit, or is quickly covered by the blowing winds of a desert storm, a fossil may form. Hard parts, such as wood, shells, bones and teeth decay less easily than soft parts, such as skin and muscles. Therefore, hard parts are more likely to be preserved.

Almost all fossils are formed in sedimentary rock, or rock that has built up in layers from small particles. These rocks lie beneath about three-fourths of the land surface of the Earth. Most sedimentary rocks contain fossils. Fossils of animals that lived in different time periods are found in different layers of rock. Generally speaking, fossils found in deeper layers are older than fossils found in layers closer to the surface.

A scientist who studies fossils is called a paleontologist. Paleontologists have learned about the Earth’s changing geography from studying fossils. From this study, paleontologists have created a geologic time chart, which divides the earth’s history in to eras.

Much has been learned through the discovery and study of dinosaur fossils. When dinosaurs lived, the earth was much different from the way it is today. Dinosaurs probably lived in an almost tropical climate. Scientist believe this is true because of the fossils of giant ferns and other swamp type plants that have been found in the same areas as dinosaur fossils.

A long series of fossils from animals and plants found in succeeding layer of the Earth’s crust tells a story about the diversity of life long ago. Fossils help scientists trace the development of life from ancient times to present day. For example, some scientists believe that present day reptiles, such as lizards, are the relatives of prehistoric dinosaurs. Other scientists believe that dinosaurs are related to present day birds. Sea lilies are relatives of prehistoric sea animals called crinoids. Trilobites are related to present-day crabs and lobsters. As these examples illustrate, fossils link the past to the present.