How old is the Earth?
Earth is about 4.54 billion years old. Scientists worked this out by dating meteorites and the oldest Earth minerals using radioactive elements that decay at known rates.
The method is called radiometric dating. Some elements, such as uranium, slowly turn into others, such as lead, at a steady rate. By measuring how much has changed in a rock or crystal, scientists can calculate its age. Meteorites formed at the same time as the planets give an age of about 4.54 billion years for the solar system.
The oldest known pieces of Earth are tiny zircon crystals from the Jack Hills in Western Australia, about 4.4 billion years old. The oldest known rocks, found in Canada, are about 4 billion years old. Older rocks have mostly been destroyed by plate tectonics and erosion.
Earth's long history
If Earth's history were squeezed into one day, the first simple life would appear early in the morning, animals would arrive in the evening, dinosaurs would live for less than an hour before 11 p.m. and modern humans would appear only in the last few seconds before midnight.
Did You Know?
In the 1600s, some scholars estimated from historical texts that Earth was only about 6,000 years old. Geology and physics later showed it is vastly older.