Final answer:
James Hutton introduced the principle of uniformitarianism, and it was later popularized by Charles Lyell. Their work suggested Earth's landscapes were shaped by gradual processes and the Earth was much older than previously believed, influencing Charles Darwin's evolutionary theory.
Step-by-step explanation:
The principle of uniformitarianism, the idea that Earth's landscapes were shaped by gradual and observable processes, was introduced by James Hutton and later popularized by Charles Lyell. Hutton, a Scottish geologist, proposed that the Earth's geologic features could be explained by processes that were still operating, which was a stark contrast to the then-prevailing belief in a young Earth shaped by catastrophic events. Charles Lyell, in his work Principles of Geology, expanded on Hutton's ideas, suggesting Earth must be far older than the few thousand years previously thought.
This insight provided a framework for understanding that the same geologic processes observed in the present have been at work in the past and thus, landscapes such as valleys formed by rivers were a result of these slow-moving geological forces. The significance of Lyell's work extended into the field of biology where it influenced Charles Darwin and his evolutionary theory, providing the necessary timescale for the gradual change in species. In short, the principles put forth by Hutton and popularized by Lyell represent a foundational shift in scientific understanding of the Earth's history and surface.