1891-1989

British geophysicist and astronomer known for his work on Earth's internal structure and earthquake travel time tables compiled with Keith Bullen—commonly known as the JB Tables. After studying tidal effects, Jeffreys proposed that Earth's core was molten rock. He opposed continental drift theory and estimated the solar system's age at several billion years. He calculated the surface temperatures of the outer planets and modeled the internal formations of Jupiter, Saturn, Uranus, and Neptune.