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25 November 2021
In northern Arizona, the Grand Canyon is a mile-deep gorge. According to scientists, the Colorado River cut a channel through layers of rock 5 to 6 million years ago, forming the canyon. In and around the canyon, humans have lived since the last ice age. Spaniards were the first Europeans to reach the Grand Canyon in the 1540s. The Grand Canyon was first protected as a forest reserve by President Benjamin Harrison in 1893, and it was made a national park by President Theodore Roosevelt in 1919.
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In northern Arizona, northwest of Flagstaff lies the Grand Canyon. It is over 270 miles long, 18 miles wide, and a mile deep, making it one of the world’s largest canyons.
Five to six million years ago, erosion from the Colorado River cut a deep channel through layers of rock that formed this natural landmark.
Some of the oldest exposed rock on Earth can be found in the Grand Canyon. A cross-section of Earth’s crust dating back nearly two billion years can be seen on the mile-high walls. The rock layers have allowed geologists to study evolution over time.
Vishnu Basement Rocks, the oldest known rocks in the canyon, are found near the bottom of the Inner Gorge. Approximately 1.7 billion years ago, magma hardened and connected this region, which was once a volcanic ocean chain, to the North American continent.
The South Rim of Grand Canyon National Park houses the Trail of Time interpretive exhibit, which traces the canyon’s geologic history. So how exactly did this vast canyon form?
In a river canyon, the water pressure of a river cuts deep into a riverbed, and the sediments from the river bed are carried downstream, resulting in the creation of a deep, narrow channel.
Other factors that contribute to the formation of canyons are weathering and erosion. In winter, the water that seeps into cracks in the rocks, freezes, expands and turns into ice. Ice causes the cracks to become larger, in the process eroding bits of stone. During heavy rains, water rushes and hits the cracks, eroding even more stone and rocks. With the crumbling and fall of more rocks, the canyon grows wide at the top.
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The Grand Canyon, 277 miles long, 18 miles wide, and 6,000 feet deep, is a product of tectonic uplift. Tectonic plates beneath the Earth’s crust shift and collide, causing an area of the crust to rise higher than the surrounding land. For millions of years, the canyon has been carved as the Colorado River cuts through the Colorado Plateau.
The age of the Grand Canyon is being debated among geologists. Some believe it may be between 5 million to 70 million years old.
The rock layers in the Grand Canyon have provided geologists the opportunity to study evolution through time. They revealed the eras and periods in Earth’s history when each of these layers was formed. They also provide a glimpse of what to expect in the future. For example, geologists estimate that the Grand Canyon is being eroded at 1 foot every 200 years and that it will continue to deepen as long as the Colorado River flows.
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