Frederick Soddy was a British chemist and physicist who was awarded the 1921 Nobel Prize in Chemistry for his theory of isotopes, a term he coined. Soddy carried out research on radioactivity with Ernest Rutherford, and later William Ramsay. In 1920 he produced an explanation of the radioactive decay of isotopes that proved invaluable in calculating geological time. Soddy and Ramsay found helium to be a product of the decay of uranium. His classic science books include The Interpretation of Radium (1909), Matter and Energy (1912), and The Chemistry of the Radio-Elements (1911–1914).