How are moon rocks used to determine the age of the Earth?
The oldest moon rocks are actually older than the oldest Earth rocks. The moon formed from accreted material that resulted from a collision between Earth and a Mars sized protoplanet. Both the Earth and the moon were molten for a period after the collision. Because of the moon’s smaller size, it’s surface cooled very quickly compared to the Earth. The solidified magma (rock) that formed the moon’s crust has been dated at roughly 4.4 billion years of age. Even though no Earth rock has been found to date this old, we can still reasonably assume that the Earth is at least that old due to the fact that the moon is formed from accreted material from the previously mentioned collision.
