Meteorites are chunks of matter that fall from outer space. Their size ranges from small pebbles to huge rocks that weigh many tonnes.
Meteorites contain radioactive atoms of uranium. Some of these radioactive atoms gradually decompose to form the stable element, lead.
Scientists have estimated that it takes about 4.5 billion years for half the quantity of uranium in any sample to turn to lead. This time span is known as the half-life of a radioactive element. So the amount of lead present in the meteorite sample is measured using a mass spectrograph and then by calculating how much of the original uranium has decomposed, the age of the meteorite is worked out.
This method, called the radiometric dating technique, has been used to find the age of several meteorites. E.g., the over 60-ton Hoba meteorite found in Namibia, the largest ever, is estimated to be 200-400 million years old.
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