Age of the Solar System
About 4.567 billion years, measured from the oldest solid grains found inside meteorites.
The age of the Solar System is usually defined as the time when the first solid materials condensed from the hot cloud of gas and dust around the young Sun. Those first solids survive as pale calcium-aluminium-rich inclusions (CAIs) inside some meteorites. Uranium–lead dating gives their age as about 4,567 million years, often written as 4.567 billion years.
We cannot get this number from Earth rocks, because our planet has been melted, eroded and recycled so thoroughly that none of its first rocks survive. The oldest known pieces of Earth are tiny zircon crystals from Western Australia, about 4.4 billion years old. Meteorites, by contrast, come from small bodies that changed very little, so they act like time capsules from the beginning.
The Allende meteorite, which fell in Mexico in 1969, has been especially important because it contains plenty of large CAIs and over 2 tonnes of it was collected. Other dates are measured from this starting point. Chondrules formed within a few million years, and Earth and its Moon took shape over the following tens of millions of years. Different studies give values differing by a million years or so.
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Level: Explorer Ages 10 and up