Sir Charles Lyell was a famed geologist and a firm supporter of Uniformitarianism - a theory that the earth was shaped by the same gradual events that are still in motion. This opposed the then-held view of Catastrophism - the idea that the earth was shaped by sudden, abrupt changes. Sir Lyell's work led him to postulate (the first one to do so!) that earth was more than 300 million years too old for its current form to be explained by Uniformitarianism. He also coined the terms Paleozoic, Mesozoic and Cenozoic, terms currently used to describe geological eras.
His work influenced Darwin greatly, who also believed in slow, gradual changes taking place over a geologic time scale in which the current forms of species evolved. The same opposition to Catastrophism (creationism in Darwin's case, which is equally arbitrary) is seen in both the works. Similarly, both their works opposed the then-held view (catastrophism and creationism) which incidentally smacked of religious fervor to them. Darwin, like Lyell, conducted extensive field studies and came up with observable evidence to support his work.
Lyell was also a close friend of Darwin and was instrumental in the publication of Darwin's paper on Natural Selection (Alfred Russell Wallace co-published, having reached the same conclusion independently).