age of the Earth

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age of the Earth

The oldest rocks found in the Earth's crust have been assigned ages of 3.96 billion (109) years from radioisotope studies, but other properties of the rocks support the belief that the planet shares a common origin with the rest of the Solar System, about 4.57 billion years ago. The cycling of the crustal material by plate tectonics (see Earth) and the eroding effects of ice, water, and wind mean that none of the earliest rocks survive intact and that evidence of an early meteoritic bombardment, so apparent on the Moon, Mercury, and Mars, is absent. See Earth; Solar System, origin.