When one views the Teton Range, visions of vast, ancient seas do not usually come to mind. The peaks seem so powerful and imposing, that it may be difficult to imagine this area covered by a sea. Both of these scenes, however, describe chapters in the geologic history of Grand Teton National Park. Fossils are the mineralized remains or impressions of plants or animals from past geologic ages, and provide geologists with clues to unravel the past history of the area.
Fossils are typically found in sedimentary rock. Many sedimentary rocks form as material such as gravel, sand, or mud settles from water into horizontal layers. With time, these layers become buried, compressed, and lithify (harden to rock). Organic material such as plant and animal remains settles along with the sediment and is buried within the layers. As the waters recede, sedimentary rocks are exposed to erosive forces such as wind, rain, ice, and gravity. These forces break down the rocks exposing each successive underlying layer. Eventually, the fossil remains of a creature once buried under thousands of feet of sediment are exposed at the earth’s surface.
In the northern, southern, and, most dramatically, in the western portions of Grand Teton National Park are extensive exposures of sedimentary formations, some over a thousand feet thick dating back to roughly 500 million years ago. Many of these formations contain the fossil remains of marine organisms. The presence of these fossils allows geologists to conclude that where the Teton Range now stands was once the floor of an ancient sea inhabited by algae, coral, brachiopods (clam-like shells), and trilobites—early ancestors of the crayfish.
Fossils do more than provide us with a fascinating look at prehistoric life forms. They are useful tools to date geologic features, analyze past climates, and trace evolutionary processes. If you are fortunate enough to find a fossil during a visit to a national park, please look but do not take. Leave the fossils to be rediscovered by other visitors and scientists in the future.
