The Colorado cuts the Grand Canyon
Two billion years made legible by one river
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The Grand Canyon is a gorge in Arizona, some 450 kilometres long and over a kilometre and a half deep, cut by the Colorado River. The canyon is due not to erosion alone but to the Colorado Plateau rising while the river already lay there and cut down just as fast. Exactly when this happened is still disputed: dates range between six and seventy million years, probably because different reaches of the canyon are of different ages and were later joined. The layers also hold one of the world's clearest angular unconformities, the Great Unconformity, where more than a billion years of history is missing entirely.
For children
The Colorado River has cut down through layer upon layer of rock, laying bare almost two billion years of Earth's history in a single wall. Walking down into the canyon is walking backwards in time — the oldest rocks lie at the bottom, by the river.
Sources
- National Park Service: Grand Canyon — Geologic Formations
- Karlstrom m.fl., Nature Geoscience 7 (2014) — canyonens alder
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