Davis, an American geographer, geologist, and meteorologist, began his varied career at the age of 20 as a meteorologist with the Argentine Meteorological Observatory. He later joined the faculty at Harvard University, where he taught for 36 years. In the 1870s, his interest shifted from meteorology to geography, and he began the study of landforms and landform evolution. Davis is credited with introducing the ideas of cyclic erosion to landscape development, proposing that the crust of the earth in a certain area is initially uplifted and is then eroded downward, passing through a precise series of sequential stages. His most noteworthy essay, "The Rivers and Valleys of Pennsylvania,"… introduced these notions of cyclic landscape evolution. Davis is known as the great synthesizer of the modern science of geomorphology and is recognized as the leader of the "America school" of physiographers. Although he was a prolific writer in all three of his fields of study, he is best remembered for his works in geography. After his retirement from Harvard in 1912, Davis remained active, lecturing and conducting field studies until his death in 1934.