Key to Oklahoma
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Prehistory to 1802

  1. Geologic History
  2. Early Peoples and Indian Civilizations
  3. European Explorers

Geologic History

Prehistory is the era before humans learned how to write. To learn prehistory, we depend on information provided by scientists called geologists. They study the earth. We also depend on archaeologists who study artifacts that ancient peoples left behind. A geological timetable made by geologists describes how and when the land was formed. Geologists now believe that the earth is at least 4 � billion years old. A geologic map shows the layers of land that have developed in Oklahoma throughout its history.

To simplify their work, geologists divide the study of time into four units: eons, eras, periods and epochs. Different rocks and minerals appeared during these times because of glaciers, erosion, volcanoes, earthquakes and other natural events. Large amounts of sedimentary rocks can be found in Oklahoma, including sandstone and limestone.

Scientists believe that life on earth began about four billion years ago. About 400 million years ago, most of Oklahoma was covered by a vast inland sea. It remained covered for about 100 million years. The water was like a thick soup and, eventually, it teemed with life. Fossil remains of fish, reptiles and other animals and plants that lived during this time can be found in rock formations in many areas of Oklahoma.

About 300 million years ago, Oklahoma was located close to the equator. But as time passed, the North American continent drifted to the north toward its present location. About the same time, pressure inside the earth caused volcanic explosions that created Oklahoma’s Quachita, Arbuckle and Wichita mountains. In all the millions of years, the earth experienced several ice ages during which time glaciers covered much of North America. One or more of these glaciers covered lands close to present Oklahoma. The last ice age developed around 18,000 B.C. Afterward, the climate became more suitable for many different forms of life.

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Mount Scott in the Wichita Mountains (Photo courtesy of Fred Marvel, Oklahoma Department of Tourism)

As mountains rose, regions around them dropped and formed large basins that filled with water where marine life continued to flourish. The two basins in Oklahoma are the Anadarko Basin in the western part of the state and the Arkoma Basin in the eastern part. Through the eons, aquifers developed below the surface. Today, 70 percent of the water that Oklahoma’s farmers use comes from these underground sources. The Ogallala aquifer under the land of the state’s Panhandle is the most important one in the state. Its value is estimated to be one billion dollars.

Over thousands of years new pressures inside the earth moved Oklahoma’s surface upward. The water drained off, and the sea receded far to the south. After millions of years in developing, Oklahoma became a homeland for humans.

The Oklahoma Museum of Natural History in Norman and the Museum of the Great Plains in Lawton have excellent exhibits about Oklahoma’s prehistoric past. The Norman museum exhibits skeletons of dinosaurs that once roamed the region before becoming extinct about 65 million years ago.

Additional Resources

bulletMore information about the geologic make-up of Oklahoma is available at the Oklahoma Geological survey web site.
bulletTo learn more about the formation of the earth and continental drift, go to the United States Geological Survey - This Dynamic Earth.
bulletTo learn more about archaeology, go to the Society of American Archaeology.

Study Guide Questions

  1. How old is the earth?
  2. What do geologists study?
  3. What do archaeologists study?
  4. What are "artifacts"?
  5. What is an "aquifer"? What is the main use for aquifers in Oklahoma today?
  6. What geological age is known as the "Age of the Mammals"?
  7. When did the first recorded earthquake happen in Oklahoma?

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