Historical geology

Historical geology is a discipline that uses the principles and techniques of geology to reconstruct and understand the geological history of Earth. It focuses on geologic processes that change the Earth's surface and subsurface; and the use of stratigraphy, structural geology and paleontology to tell the sequence of these events. It also focuses on the evolution of plants and animals during different time periods in the geological timescale. The discovery of radioactivity and the development of several radiometric dating techniques in the first half of the 20th century provided a means of deriving absolute versus relative ages of geologic history.

Economic geology, the search for and extraction of fuel and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, including most importantly the geologic hazards of earthquakes and volcanism, must also include a detailed knowledge of geologic history.

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 concepts 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 and Charles Lyell also contributed to early understanding of the Earth's history with their observations at Edinburgh in Scotland concerning angular unconformity in a rock face and it was in fact Lyell that influenced Charles Darwin greatly in his theory of evolution by speculating that the present is the key to the past. Hutton first proposed the theory of uniformitarianism, which is now a basic principle in all branches of geology. Hutton also supported the idea that the Earth was very old as opposed to the prevailing concept of the time which said the Earth had only been around a few millennia. Uniformitarianism describes an Earth created by the same natural phenomena that are at work today.

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