 Here you see a cross-section of a mountain, and you see the layers the rocks in the mountain. These started out horizontally, but now you see where they've been broken and turned and flipped and all sorts of things have happened to them over geologic time. How do we know what happened to them? Let's go back hundreds of millions of years and see what happened, how these layers got to the point they are. We start with some mud that is washed in by rain and streams. The sun comes out, it dries out the mud, and the mud cracks, and you get these little cracks at the surface going down. After a while another layer of mud is washed in, it fills the dried out cracks. Next, a dinosaur comes stomping through, leaving his tracks in the second layer of mud. More mud washes in, raindrops plop into that and make little pock marks in the surface, and another layer of mud and a little erosion and more layers and on and on through geologic time. But while this sediment is piling up, other things are happening. Plate tectonics drifting continents are out there, and eventually a collision starts, and the rocks start to bend and break and fold as they're being smashed by the great tectonic forces that are going on. And during this, some of the layers are tilted, some of them can be even turned upside down. Now you can see we have reached the modern condition with this beautiful history behind it, and you can see how it happened. So take a brief look here at how this image appears to where we started from the first deposits, and I hope you can see the history of geology here.