It's difficult to look at a modern bird and fossils of some theropod dinosaurs and not see a connection. It's equally difficult to imagine the changes in the Earth's crust that must have occurred in order to lift a marine fossil to a mountain top. The Earth is over 4.5 billion years old. The possibilities for change over that period of time are enormous. During the course of this thread, we will discuss how our understanding of the origin of life has changed. We will examine the role played by natural selection and look into those factors that influence natural selection. How do species change over time? What kinds of conditions need to exist in order for change to occur? What is the role of mutation in the process?