What role does the moon play in the evolution of life on Earth? Is the moon drifting away? How fast? How far would it have to drift before there is a noticeable change on Earth?
Suzanne,
The moon and its significant role in the evolution of our Earth deserves an entire book, but let me summarise some of the most interesting parts:
The moon formed from a collision between a proto-planet (named ‘Theia’) and our proto-Earth about 4.5 billion years ago. The molten rocky debris scattered into orbit about the Earth coalesced into the moon – which is literally made in part from material that was once inside the Earth. This explains why the composition of the moon is very close to that of our planet.
Our moon is responsible for causing two tides in the ocean each day. This is because the pull of gravity from the moon is slightly stronger on the side of the Earth that is facing the moon at any point in time because that point is closer – the moon literally squishes the Earth into a shape like an egg, although we are talking about just a few meters in shape difference from a sphere. The ‘egg shape’ always points at the moon, so as the Earth spins, the entire planet is continuously being deformed and the ocean tides are due to the time difference it takes for the land and water to recover from this time dependent shape change. The water literally ‘sloshes’ over the two bulges on the Earth.
There are a couple of other effects that cause the rate of spin of the Earth to slow down and to cause the distance to the moon to increase with time. Due to a lag in the time it takes for the ‘egg shaped Earth’ to deform back to a sphere, the Earth and moon shapes do not point exactly at each other. There is whats called a ‘torque’ on the spin of the Earth and also a similar back-reaction on the moon. In addition, there is significant loss of energy due to heat generated by the compression and motion of material inside the Earth & the water sloshing over the Earth’s crust. Over time, the day has gotten a lot longer – billions of years ago, the day was just a few hours long! We can find evidence of this in the growth rate of fossilized coral which is sensitive to the length of the day and the lunar month.
The continuous deformation of the Earth’s shape is replicated on the moon due to the similar gravitational force of the Earth on the moon. The spin of the moon has also slowed down over time, so much so that we now only ever see one side of the moon! This is called ‘tidal locking’ in astrophysics language. In the distant future, the Earth will rotate exactly once every lunar month (which will be about 60 days long) so that one side of our planet will always be facing the moon – future generations living on the ‘dark side of the Earth’ may never see the moon for themselves. Don’t worry, this is not going to happen soon but in a few billions of years from now.
The implications for life are fascinating. When the moon formed it was much closer to the Earth – perhaps ten times closer. The moon moves away since the total energy of the Earth-moon system must be conserved. In fact by bouncing a strong laser onto mirrors left on the moons surface by the Apollo astronauts in the 60′s, we can measure the distance to the moon to an accuracy of about 1mm and we know that every year the moon moves about 4cm further from the Earth. The moon will eventually come to rest at about twice its current distance, when both the Earth and moon will be tidally locked, at which time the tides will not be strong enough for surfing, so enjoy the ocean whilst you can 
It’s a simple calculation to show that the height of the tides is proportional to the distance to the moon^3, i.e. if the moon was once ten times closer, the ocean tides were 1000 times higher! So in the distant past, when water first appeared on Earth from the icy bombardment of comets, there were tidal waves nearly a km high crossing over the land every few hours. Not a good time for life to crawl out of the ocean!!!
There is another interesting fact about our moon. All the planets without their own moon, or with a small moon, are spinning chaotically. Small perturbations can cause their spin axis to change – dramatically and rapidly. Fortunately, our massive moon stabilises the spin axis of the Earth. Without our moon, on a short timescale, life evolving on the equator would have suddenly found itself at the new ‘North Pole’. Not a good situation for the first immobile life forms to face.
Enjoy our moon, we wouldn’t be here without it.
Ben