Nearly half of Earth’s history is exposed in the walls of the Grand Canyon in northern Arizona, USA.
Grand Canyon National Park is a natural geology textbook, and each layer of rock or stratum is a page of that history. To hike down the canyon is to walk back into time. The rocks of the upper canyon are relatively soft, flat-lying sedimentary rocks—limestone, sandstone, and shale deposited in ancient shallow seas, beaches, and swamps.
Erosion by the Colorado River and gravity-powered mass wasting have combined to create an upper gorge that is up to 18 miles across. At river level, 2 billion-year-old igneous and metamorphic rocks of the narrow inner gorge mark the remnants of ancient mountains.
Photo from here.
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