PPT Slide
Notes:
We know about these tremendous changes in the earth, in part, from fossils. While some of the dynamic processes on our earth, like volcanoes, have resulted in helping to preserve these clues to ancient life and climate, there are other natural processes that help to destroy them. 35 million year old petrified redwood trees are broken apart in a very, very small fraction of that time by freeze\thaw cycles in which water filling small cracks in the petrified wood is frozen and expands, pushing the wood apart.