James Hutton, a Scottish physician and farmer, is considered by many to be the "father of geology." Hutton observed geological changes and theorized that the forces which were changing the landscape of his farm were the same forces that had changed the earth's surface in the past. He built on this theory to form his "Principle of Uniformitariansm" in 1785.

This principle states that current geological processes, for example volcanic activity and erosion, are the same processes that were at work in the past, and will still be at work in the future. A summary of his theory is the phrase "the present is the key to the past." He watched these slow changes occurring on his own farm and theorized that over time, a stream could carve a valley, rain would erode rock, and sediment could accumulate and form new landforms. He realized that these forces must be...