Historical geology is the use of the principles of geology to reconstruct and understand the history of the earth. It focuses on geologic events that change the earth's surface and the use of stratigraphy to tell the sequence of these events. It also focuses on the evolution of plants and animals during different time periods in the Geologic timescale.
Nicolaus Steno (also known as Niels Stensen) was the first to observe and propose some of the basic concepts of historical geology. One of these concept was that fossils originally came from living organisms. The other, more famous, observations are often grouped together to form the Laws of Stratigraphy. James Hutton also contributed to early understanding of the earth's history with his observations at Edinburgh concerning an angular unconformity in a rock face. He first proposed the theory of uniformitarianism which is a basic principle in all branches of geology. Hutton also supported the idea that the earth was very old as opposed to prevailing theory at the time which said the earth had only been around a few thousand years. Uniformitarianism describes an earth created by the same forces of sun, wind, and water which are at work today. The opposing theory, catastrophism, says that the earth was created by a series of various sorts of cataclysms or catastrophes, similar to the story told in the Bible. This theory was once thought to be invalid but, with the recent advent of extinction theories based on meteor impacts, may be making a comeback. Perhaps the truth is somewhere in between the two ideas.