How did the Moon form?

• 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.

Sources:

1. NASA
2. History Channel