Uniformitarianism

Layers of rock take a certain amount of time to form; the most massive outcrops of rock can only form in millions of years.

Unlike conventional thinking at the time, Hutton believed Earth was millions of years old. One consequence of uniformitarianism is the understanding that extensive rock bodies take huge spans of time to develop, which was one reason Hutton came to believe in ancient Earth. Scientists have set up models that simulate the formation of sedimentary rocks from river sediments at present-day sedimentation rates. The results—rock layers form extremely slowly. Thus, rock layers as thick as those seen in places like the Grand Canyon could only have formed over spans of millions of years.

Hutton’s ideas were advanced by another scientist, Charles Lyell (1797 to 1875), who wrote Principles of Geology, and established uniformitarianism as the method for interpreting the geologic history of Earth. Today, this principle is used in geology to assert that most structures on Earth formed by the slow, gradual work of the same processes that work today, such as erosion and tectonic movement. 

Summarize the principle of uniformitarianism in your own words and explain why you think it is so important to our understanding of the past.

The principle of uniformitarianism states that the laws of nature do not change. This implies that we can decipher what went on in the past by knowing how things work today. This is important to our understanding of Earth’s history because we cannot physically go back in time and study how things happened on ancient Earth. We can, however, assume that the processes that happened in the past are the same processes we see today.