4.5 Billion years ago infant Earth bombarded with incoming bouldering rocks, slowly grew in size with solid crust, thick mantle and iron core.
A MARS sized neighboring planet named THEIA intruded into Earth’s orbit and collided with the Earth.
The impact resulted in vast portions of mantle from both Earth and Theia ejecting out into space forming an orbital ring revolving around the Earth.
The ejected mantle orbiting around the Earth collided and coalesced into a new companion: The MOON. It took 150 million years for the Earth to stabilize and its molten crust to re-harden.