Much of the science of geology deals with the history of the earth. The evidence is in rocks, which may seem lifeless but are really incredible storytellers. If the lava that shoots out of Kilauea volcano in Hawaii cools into a smooth black rock called basalt, an old basalt in a rock pile tells us that a Kilauea-like volcano once erupted nearby, even if the volcano has long since eroded away. Although there may be different environmental conditions in different places or times, e.g. the Earth had no free oxygen before photosynthetic plants evolved, scientists assume that the physical and chemical laws of nature are the same for all time periods and all planetary bodies. This is called uniformitarianism .
Geologists look for places where they can most easily and accurately interpret the earth's history.
And there is probably no more spectacular place to do this than the Grand Canyon in northern Arizona, in the United States. It's as if each rock layer is a chapter in a book about the geologic history of northern Arizona. Inc. All rights reserved.