Yet Another Snippet from "A Short History of Nearly Everything" by Bill Bryson

“We’re a twin planet. Not many of us normally think of the Moon as a companion planet, but that is in effect what it is. Most moons are tiny in relation to their planet. The Martian satellites of Phobos and Deimos, for instance, are only about ten kilometers in diameter. Our Moon, however, is more than a quarter the diameter of the Earth, which makes ours the only planet in the solar system with a sizeable moon in comparison to itself, and what a difference that makes to us.

“Without the Moon’s steadying influence, the Earth would wobble like a dying top, with goodness knows what consequences for climate and weather. The Moon’s steady gravitational influence keeps the Earth spinning at the right speed and angle to provide the sort of stability necessary for the long and successful development of life. This won’t go on forever. The Moon is slipping from our grasp at a rate of 1.5 inches a year. In another two billion years it will have receded so far that it won’t keep us steady and we’ll have to come up with some other solution, but in the meantime you should think of it as much more than just a pleasant feature in the night sky.”