Geologic Fact Two:

Early in Earth's history, a young planet, Theia, crashed into us. Had it been a head-on collision, both planets would've been destroyed. Instead, pieces of Earth and Theia's remains blasted into space. Thanks to gravity, it eventually pulled the rubble together, creating a ring of dust and debris. From this ring, our Moon formed.

At first, because the Moon was so close to Earth and because of Theia's impact, days only lasted six hours. Over time, though, the Moon moved away, and days became longer.