Earth is actually made up of two planets, scientist have found.
A young Earth was mixed with a baby planet called Theia, following a head on collision 4.5 billion years ago that was so violent it also formed the Moon.
It was thought that the Moon was created when Theia grazed the Earth and broke apart which sent a smaller chunk into space which was caught in Earth's gravity.
However scientists have now matched oxygen particles from the Moon with Earth and concluded they are identical.
Edward Young, leader of the study, said: "Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them."