 Alfred Wegener proposed a theory in 1912 that the great continents of the Earth had drifted over geological time and were once all joined together in a giant landmass we now call Pangea. His idea was based on the way the present continents fit neatly together and by the way bands of fossil bearing rocks join up across continents like this. Unfortunately, Wegener was unable to provide a mechanism for this movement and his theory was ridiculed by the scientific community until 1965 when the theory of plate tectonics was published. This proposed that the continents were moved around on great plates driven by convection currents in the hot mantle of the Earth. For details, see our related video. Perhaps the most dramatic evidence came from the magnetism of rocks each side of the mid ocean ridges. When rocks solidify they become weakly magnetic in the direction of the Earth's magnetic field. However, every few million years the Earth's magnetic field flips so the North magnetic pole becomes South Pole and vice versa and this change is signaled in the rocks. Scientists found that the rocks each side of the mid ocean ridge were magnetized first in one direction and then in another like this. Magma solidifies locking in the magnetism, new magma forms as the plates move apart, the magnetic field reverses, more magma solidifies locking in the reverse polarity and so on creating a pattern that repeats each side of the ridge with the rocks getting older the further you are from the ridge. Clear evidence of the ocean moving apart over millions of years. Further evidence came from plotting where Earth's volcanoes and earthquakes were situated. From this map you can see that they form lines around the globe marking out the edges of the great tectonic plates. You get almost all earthquakes and volcanoes at plate boundaries. And finally we find the great mountain ranges right alongside where two plates are pushing into each other. The Himalaya are being thrust upwards as India moved and is still moving slowly into Asia. And as the Pacific plate is subducted under the Asian plate the islands of Japan with many earthquakes and volcanoes and the deep ocean trench to the east were formed and are still being formed.