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RADIOACTIVE DATING

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Scientists use radioactive dating to calculate the age of the Earth. All the uranium on Earth will eventually, with precise yet fantastic slowness, become lead. An isotope of uranium will take 2250 million years to become 25% lead. By measuring the proportion of uranium and lead in rocks they have found the age of the oldest rocks to be 3600 million years. Older rocks may yet be discovered. However, our planet existed before rocks started to form. To estimate how much older the Earth is than its oldest rocks, scientists calculate the age of meteorite fragments using radioactive dating, as it is assumed that all of the Solar System came into being at the same time. The age of the Earth is generally accepted as 4500 million years.