ELI5: Explain Like I'm 5

Giant impact hypothesis

Long long time ago, when the solar system was very young, there were lots of rocks and dust flying around in space. One of these rocks was about the size of Mars and was floating around the sun just like Earth.

One day, this rock and the Earth were in the same place at the same time. They got so close to each other that they collided really hard. This collision was so strong that it made rocks and dust fly everywhere!

This giant impact caused a lot of damage and the rock and the Earth both changed shape. Some of the pieces that flew off even started orbiting the Earth and eventually became the Moon that we see in the sky today!

This is the giant impact hypothesis - the theory that the Moon was formed by a big collision with the early Earth. Scientists have studied the rocks on the Moon to learn about this event and it has helped us understand how the planets in our solar system were formed.