Final answer:
Sir Charles Lyell influenced Darwin with the principle of uniformitarianism, extending the perceived age of Earth and promoting the idea of gradual geological changes, which paralleled Darwin's thoughts on biological evolution.
Step-by-step explanation:
Sir Charles Lyell, known as the father of modern geology, influenced Darwin with the principle of uniformitarianism. This principle, detailed in Lyell's work Principles of Geology, asserts that the forces that have shaped the Earth's surface, such as erosion and sedimentation, have been the same throughout Earth's history and have occurred over a very extended period of time.
This idea was significant because it proposed that the Earth was much older than the commonly held belief of a few thousand years. By suggesting a much greater age for the Earth, Lyell provided a timeframe that allowed for the slow and gradual processes necessary for biological evolution, something that proved crucial to Darwin's development of the theory of natural selection.
Lyell's ideas not only altered the perceived age of the Earth but also supported the concept that small, gradual changes could culminate in significant transformation over time, an analogy that Darwin applied to biological evolution in species.