What would Earth look like with no Moon?

James - This question refers to the giant impact hypothesis, our best guess as to how our moon formed. It's the idea that the earth collided with another planet, which set both bodies on the path to their present trajectories, and we've been able to track down just the man who can help with your question. Dana Mackenzie is the author of 'The Big Splat, Or How our Moon came to be'. I asked him what Earth would've been like before the giant impact.

Dana - To be honest, James, we don't know much about the Earth before the impact because whatever was there before was totally scrambled. A lot of the impactor lunged into Earth, some of it was blown off into space and also a lot of Earth's mantle was churned up and thrown out. All this material made a disc sort of like the disc around Saturn, but much denser, much less stable. And so that disc rapidly coalesced and formed our Moon. And this was about four and a half billion years ago. What are some effects of the giant impact? So first of all, the length of our day 24 hours is governed by the Earth's rotation. That rotation rate was set by this giant impact. In fact, that impact was oblique and set the Earth spinning at about once every eight hours. So we had eight hour long days. Gradually over the billions of years since then, our days have slowed down to our present 24 hours. But it's fair to say that we would have slower days, even than that, if we had never had the giant impact. Another big effect of the impact is tides, because we have a Moon. Our Moon is larger relative to our planet than any other body in the solar system except for Pluto. So the moon has an outsized effect on our planet. A lot of people think that tide pools are where life evolved, the first life, and so possibly the Moon has given us life. In any case, it certainly gave us tides. Another interesting thing, the results from the impact is the Earth's tilt. So our planet is tilted by about 23 degrees, and that's what gives us our seasons. We might have had life without the Moon, but life would certainly have been different if we hadn't had seasons. Another important aspect of the having a Moon, having the giant impact is that the Moon actually stabilizes Earth's rotation. So over the millions of years, the axes tend to move around a little bit, and this moving around has been much more pronounced in Mars, for example. And so they've had much more dramatic climate swings. You know, our poles move a little bit, but not a lot, and that has perhaps contributed to the stability of Earth climate.