Continental drift

Fossil records suggesting that continents now separated were once together: see Pangaea

First known illustration of the opening of the Atlantic Ocean, by Antonio Snider-Pellegrini, 1858.

Continental drift is a historical theory. The theory was first proposed by Abraham Ortelius in 1596. It was fully developed by the German geologist and meteorologist Alfred Wegener in 1915.

The theory said that parts of the Earth's crust moves slowly on top of a liquid core. The theory has now been included in the wider theory of plate tectonics.

Evidence

The theory was supported by finding the same rocks and fossils in western Europe and the eastern North America. There are also similar fossils on the western coast of Africa and the eastern South America. The shapes of these continents nearly fits together. The theory was plausible (believable), but there was no known mechanism to drive these great movements. This problem was later solved by plate tectonics.

The pattern of volcanic activity, mountain building (orogeny) and earthquakes is explained by continental drift. The existence of identical rocks widely apart supports the theory.

Examples (there are hundreds):

1. Fossils of the fern Glossopteris are found in rocks from Australia, South America, Antarctica, India, Africa and Madagascar. These were all together in the supercontinent Gondwana, after the global continent Pangaea broke up.
2. Table Mountain at the Cape of Good Hope, South Africa, and mountains south of Rio de Janeiro are made of identical rocks. This corresponds to the fit of Africa with South America in Pangaea.
3. The Giant's Causeway in Northern Ireland, and Fingal's Cave on Staffa, Inner Hebrides, Scotland is the same rock formation.

Mechanism

The basic machine driving continental movement is heat moving from the Earth's mantle through the crust and out of the planet. The effect of this it to cause convection, and plate movement.

Two events in particular are of huge importance:

1. The production of new crust at places such as the Mid-Atlantic Ridge.
2. The removal of crust by subduction (moving under) at the points where plates collide.