Sir Charles Lyell, 1st Baronet (1797-1875) was an English lawyer and the foremost geologist of his day. He is best known as the author of Principles of Geology (published in three volumes in 1830-33), which popularized James Hutton's concepts of uniformitarianism; the idea that the earth was shaped by slow-moving forces still in operation today. The central argument in Principles was that the present is the key to the past. Lyell's interpretation of geologic change as the steady accumulation of minute changes over enormously long spans of time was a powerful influence on the young Charles Darwin. Lyell's geological interests ranged from volcanoes and geological dynamics through stratigraphy, paleontology, and glaciology to topics that would now be classified as prehistoric archaeology and paleoanthropology. He died in 1875 while revising the twelfth edition of Principles. He was 77 years old.