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Meteorites II

April 18, 2015

The solar system is about four-and-a-half billion years old. One of the major lines of evidence to determine that age comes from meteorites.

Most meteorites are pieces of asteroids — chunks of rock and metal that orbit the Sun. Some of these meteorites contain radioactive elements and their daughter elements, which form when the radioactive materials decay.

The radioactive materials were created by a supernova that exploded shortly before the birth of the solar system. Debris from the supernova “seeded” the cloud from which the solar system formed with many elements.

The radioactive elements form a natural atomic clock.

Scientists know how long it takes any radioactive element to decay to form its daughter element. Uranium-238, for example, has a half-life of four-and-a-half billion years. At the end of that time, half of a given sample of the element will have decayed to form lead-206. So comparing the amount of uranium to lead in a meteorite tells you how much of the original uranium has decayed, which tells you how long the sample’s “clock” has been ticking.

Scientists look at several elements to get a more complete understanding of the age. And they have to make a few assumptions about the composition of the cloud that gave birth to the solar system.

Any way they look at it, though, they get the same age. The oldest meteorites are a bit more than four-and-a-half billion years old, which means the solar system is that old as well.


Script by Damond Benningfield, Copyright 2015

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