Continental drift

Abstract

During the nineteen-twenties and thirties there was a vigorous controversy as to whether the continents have moved. The arguments largely concerned similarities between now-separated continents. These similarities did not provide direct evidence of motion. There is now direct evidence for motion of hundreds of kilometres and perhaps of over 1000 km on transcurrent faults. Palaeomagnetism also has provided strong evidence for movement, the only alternative being to suppose that before the Eocene the Earth's magnetic field was nothing like a dipole and was not related to the axis of rotation. Recent work on the oceans makes it difficult to believe in 'land bridges' or 'lost continents'. The only plausible mechanism for moving the continents is thermal convection in the mantle with rising currents beneath the oceans. This leads to the suggestion that the oceans may be widening by tension cracks along the crests of the mid-oceanic ridges.