1596

• Abraham Ortelius was a map maker and the first to notice the geometrical coincidence between the coasts of America and Europe-Africa, and how they fit together like puzzles pieces. He attributed continental drift as the reason.

1785

• James Hutton theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. The law of superposition states sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.

1912

• Albert Wegener suggested that a supercontinent he called Pangaea had existed in the past, broke up starting 200 million years ago, and that the pieces "drifted" to their present positions. He cited the fit of South America and Africa, ancient climate similarities, fossil evidence (such as the fern Glossopteris and mesosaurus), and similarity of rock structures.

1960

• Harry Hess discovered what he called sea floor spreading. He proposed that hot, less dense material below Earths crust rises toward the surface at the mid-ocean ridge. Then, it flows sideways, carrying the seafloor away from the ridge in both directions. As the sea floor spreads apart, magma moves upward and flows from cracks. It becomes solid as it cools and forms a new seafloor.