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Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Laura Blackstone, Yellowstone Geology Program guest scientist, and Jefferson Hungerford, park geologist at the Yellowstone Center for Resources.

Many people understand that Yellowstone National Park is unique because it hosts more than half of Earth's geysers, mudpots and thermal springs. The park is also unique because it contains rock formations that span more than half the Earth's 4.6-billion-year lifespan. These rock formations tell stories of the sinking, pulling, contracting and twisting of an ever-changing landscape.

In the Paleozoic era (542 to 251 million years ago), sea levels rose and fell while the Yellowstone area was close to the equator, due to the ever-shifting nature of Earth's tectonic plates. Layers of limestone, shale and sandstone record periods of deposition in shallow marine environments, like the present day Bahamas and U.S. East Coast. These rocks can be seen in the mountains of the Gallatin Range on the western border of the park.