Dating rocks by radioactivity

Posted by / 24-Aug-2019 19:35

Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.

After all, the ever-changing Earth rarely left a complete geological record.

For example, isotopes with very long half lives are no good for dating rocks younger than about 100 million years.

Scientists discovered that rocks could be timepieces -- literally.

Many chemical elements in rock exist in a number of slightly different forms, known as isotopes.

For example, about 1.5 percent of a quantity of Uranium 238 will decay to lead every 100 million years.

By measuring the ratio of lead to uranium in a rock sample, its age can be determined.

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Using this technique, called radiometric dating, scientists are able to "see" back in time.