Astronomy
The Moon

Was the Moon ever part of Earth?

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10/21/2016

The close similarity of the Moon's composition and the Earth's crust suggest that they had a common formation. One theory is that a large co-orbiting planetoid struck the Earth after the heavier elements had already formed the core (Giant Impact or Massive Collider theory). Some of the collider's exterior and some of the Earth's outer layers were smashed loose and coalesced into the Moon, which gradually moved farther from the Earth.

Because the isotopic composition of lunar crust proved to be practically identical to Earth's, the Giant Impact may have involved two smaller proto-Earths instead, whose compositions then combined.