Luna

This here is NASA's Astronomy Picture of the Day from March 20, 2012. It's a short video demonstrating the evolution of the moon. One thing that I really like about this is the fact that it shows how a rocky body without an atmosphere evolves over time as it sweeps out it's orbit.

Another thought that this video provokes is what if the Earth's atmosphere didn't protect us from meteorites? What would the Earth look like if every piece of rock or space dust that the Earth came into contact with was not disintegrated in the atmosphere? For starters, there would be thousands more craters. Craters everywhere. Where your house is would probably be a small crater from some small asteroid that came hurtling toward the Earth. 

Climates would be extremely different. Think of all of the waves that would be caused by meteorites smashing into the ocean. Of course, these would be fairly small for the most part, but once in awhile you'd get a nice sized meteorite slamming into the ocean with enough energy to, perhaps, cause a tsunami of some sort. I don't even know how it would effect forests with the blast radii of all of the meteorites. Would plants survive such an event?

Also, what would happen to the night sky? Meteor showers wouldn't exist. Instead we'd probably live in fear of the meteorites smashing into our house at random. All of those streaks of light that we see during meteor showers and regularly throughout the year would be instead a rock slamming into the ground with surprising effects.

Of course, this is all assuming that the space rocks are able to pass freely through the atmosphere, which is obviously not the case. Because our atmosphere protects us from the meteorites we don't have to worry about things like a small meteorite taking out a bridge or something like that. The only things we have to worry about are comets, meteors, and the like which periodically pass by the Earth. What would we do if one were to be on a collision course with Earth? Could we do anything?