Oldest Rocks

Rocky Mountain National Park
Rocky Mountain National Park

NPS Photo/M.Reed

During the immense span of time that has elapsed since life first emerged on the Earth 3.4 billion years ago, environmental conditions have changed and different groups of plants and animals have appeared, flourished, and disappeared. Our knowledge of this history is derived from the rocks that comprise the crust of the Earth. Over the years scientists have written the geological history of the earth by studying the composition, structure, and relationship of rocks and the fossils they contain.

The oldest rocks in the parks are Precambrian in age, from 3 billion to 600 million years old. This time interval saw the development of algae, fungi, and soft-bodied marine plants and animals. The distribution of Precambrian rocks is worldwide, but in the United States rocks of this age are found in the cores of major mountain ranges. They also occur in the Lake Superior region and in a few localities in the southwest.

map of the US lower 48 states showing generalized occurrence of rocks of different geologic age

Precambrian Geology - East

Precambrian Geology - West

Last updated: October 26, 2020


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