| Themes > Science > Paleontology / Paleozoology > About Paleontology / Paleozoology, Generalities > Geologic Time > Relative Time |
The record of past events which took place on the surface of the earth is entombed within the rocks. Although some information can be gleaned from igneous and metamorphic rocks, these rock types mainly record events which took place at depth, and help us unravel plate tectonic events. Much of the information available about surface events is linked to those rocks which formed at the surface, sedimentary rocks. Covering some 70% of the earth's surface, these rocks have two characteristics which are of central importance for time considerations. Firstly they are layered, and secondly they contain fossils. The question is, how can geologists decipher the available record? To use an analogy, the record we have is the equivalent of loose-leaf rock diaries, utterly lacking dates, scattered all over the earth, whose pages have been subjected to the ravages of erosion. Moreover, the story was written in a language which we can understand only if we understand the processes we can see going on today and assume that the same processes that operate today also operated in the past. This concept of uniformitarianism was first understood and enunciated by the person we consider the father of geology, James Hutton. |
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