Two of Jupiter's satellites, Europa and Ganymede, pull Io into an elliptical orbit around Jupiter. Differences in the strength of Jupiter's gravitational pull as the distance between the planet and Io varies causes slight changes in Io's shape. Scientists believe that Io heats up internally when it changes shape.
The Atomic Age, also known as the Atomic Era, is the period of history following the detonation of the first nuclear (atomic) bomb, Trinity, on July 16, 1945 during World War II.
The age of Earth was calculated to be about 24-40 million years based on the laws of thermodynamics. Unknown at the time was that the Earth has an internal heat source (radioactive decay) In 1899, John Joly (Irish) calculated the rate of delivery of salt to the ocean.