Example of relative dating methods
The only disturbance that the layers experience is bioturbation, in which animals and/or plants move things in the layers.
however, this process is not enough to allow the layers to change their positions.
Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.
A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." The principle of intrusive relationships concerns crosscutting intrusions.
He also found that certain animals were in only certain layers and that they were in the same layers all across England.