Age of Earth

The age of Earth is estimated to be 4.54 ± 0.05 billion years. This age corresponds to the final stages of Earth's accretion and planetary differentiation during the early Hadean eon. Estimates are based on radiometric dating of meteoritic material—the ages of which are approached by those of the oldest-known terrestrial material and lunar samples—and accretion models consistent with observations of planet formation in protoplanetary disks.

Following the development of radiometric dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The oldest such minerals analyzed to date, small crystals of zircon from the Jack Hills of Western Australia, are at least 4.404 billion years old. Calcium–aluminium-rich inclusions (CAIs), the oldest known solid matter that formed within the Solar System, are 4.5673 ± 0.00016 billion years old, giving a lower limit for the age of the Solar System.

It is inferred that the accretion of Earth began soon after the formation of CAIs. Because the duration of this accretion process is not yet adequately constrained—predictions from different models range from around 30 to 100 million years—the difference between the age of Earth and of the oldest rocks is difficult to determine. It can also be difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.