Radiometric dating
A way of finding the age of a rock by measuring how much of a radioactive element has turned into another element.
Some atoms are unstable. Over time they change, or decay, into different atoms, at a steady rate that heat, pressure and chemistry cannot alter. The original atom is called the parent and the new one the daughter. Radiometric dating works like an hourglass: if you know how fast the sand falls and measure how much has collected at the bottom, you can work out how long the timer has been running.
Scientists crush or separate a sample, then measure the amounts of parent and daughter atoms using a mass spectrometer, an instrument that sorts atoms by weight. Different pairs suit different jobs. Uranium decaying to lead measures billions of years, while carbon-14 is used for thousands of years.
Radiometric dating has shown that the oldest solids in meteorites formed about 4.567 billion years ago. The best-known measurements come from white inclusions in carbonaceous chondrites such as Allende, which fell in Mexico in 1969. The same methods can also date when a meteorite was melted, shocked by an impact, or fell to Earth. When you see an age written with a plus-or-minus figure, such as 4,567.3 ± 0.2 million years, that is usually a radiometric age with its uncertainty.
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Level: Explorer Ages 10 and up