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Determining the age of Earth has been a difficult problem in the history of science. A. Herodotus attempted to calculate Earth's age by observing sediment deposits, but modem principles for estimating Earth's age from geologic processes arose from the work of Steno and Hutton. B. Hutton described the effects of wind and water on masses of uplifted rock and was the first to suggest that much of the sedimentary record was missing due to erosion. C. Gaps in the sedimentary record began to be recognized by Kant and were later made clear by physicists studying the Sun's sources of energy. D. Early estimates of Earth's age based on the rates of geologic processes were inaccurate, and calculations based on estimates of the Sun's age and energy source were also extremely low. E. Radio isotopic dating, made possible by the discovery of radioactivity, and the discovery of nuclear fusion cleared up questions about both Earth s age and the Sun's energy source. F. In the 1960s scientists moved from analysis of meteorites to refinements of solar evolution models and determined the age of the solar system to be at least a billion years.