The Scottish geologist, James Hutton, in the mid 1700's put forth the ides of "uniformitarianism". Hutton put forth that the processes that shape the Earth today are also the processes that shaped the Earth in the past. many of these past geologic events are recorded in sedimentary rocks. Sedimentary rocks record events such as volcanic eruptions and also contain fossils.
Fossils are the remains of prehistoric life preserved in sedimentary rocks. Igneous and metamorphic rocks do not contain fossils as the heat and pressure would destroy any evidence of past life. Below are listed some characteristics of fossils:
- the type of fossil depends on the conditions where the organism died and how it was buried
- organisms need hard parts and rapid burial
- the faster the burial, the greater the chance of a fossil being formed.
- animals with hard parts, see fossilized horse above right, stand better chance of becoming a fossil.
- petrified wood, above left, is a fossil whose remains have been altered.
- dinosaur footprints and other types of tracks are referred to as molds.