Final answer:
The concept of uniformitarianism suggests that the Earth is constantly shaped and reshaped by natural forces working over vast stretches of time, in contrast to catastrophic events. This idea was proposed by Scottish geologist Charles Lyell and is based on the principle that the same geologic processes operating in the present have operated in the past.
Step-by-step explanation:
The concept of uniformitarianism suggested that the earth is constantly subject to shaping and reshaping by natural forces working over vast stretches of time. This idea was proposed by Scottish geologist Charles Lyell, who argued that the same geologic processes operating in the present had operated in the past, and at the same rate. According to the principle of uniformitarianism, gradual and continuous processes like erosion and deposition shape the Earth's surface over millions of years.