Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit, making the Moon's orbit bigger (but, a bit pardoxically, the Moon actually moves slower!). read more
The Earth would also adjust to its two moons, giving life a chance to arise. But life on a two-mooned Earth would be different. The combined light from the Moon and Luna would make for much brighter nights, and their different orbital periods will mean the Earth would have fewer fully dark nights. read more
While Comins's book is hypothetical, some researchers theorize that the Earth already has two — or sometimes more — moons. These scientists argue that we pick up small asteroids that make several orbits around the Earth over a period of a few weeks or months before taking back off into space. read more