1837 - Louis Agassiz begins his glaciation studies which eventually demonstrate that the Earth has had at least one Ice Age
1862 - Lord Kelvin attempts to find the age of the Earth by examining its cooling time and estimates that the Earth is between 20--400 million years old
1903 - George Darwin and John Joly claim that radioactivity is partially responsible for the Earth's heat
1907 - Bertram Boltwood proposes that the amount of lead in uranium and thorium ores might be used to determine the Earth's age and crudely dates some rocks to have ages between 410--2200 million years
1960 - Harry Hess proposes that new sea floor might be created at mid-ocean rifts and destroyed at deep sea trenches
1963 - F.J. Vine and D.H. Matthews explain the stripes of magnetized rocks with alternating magnetic polarities running parallel to mid- ocean ridges as due to sea floor spreading and the periodic geomagnetic field reversals