People have had a lot of ideas about how the Moon formed.
Most scientists believe a small planet-like body smacked into Earth about 4.5 billion years ago. Our planet was still young then. It was only 100 million years old! The crash threw pieces of rock into orbit. The pieces joined and became the Moon. Both Earth and the Moon spent the next 700 million years being hit by big meteorites. Earth’s scars from that time have mostly healed. That’s because of the weather, erosion, and plant life on Earth. But the Moon still has big pockmarks, called craters.
The last part of the Moon’s formation took place over the next 2 billion years. Hot lava came up from below the surface. It formed dark areas called maria (MA-ree-uh), or seas. As this process slowed down, the surface got harder. It turned into the grayish-green crust we see today.
