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Plate tectonics

 Plate tectonicsWhy is the Earth like a jigsaw puzzle? And was it ever possible to walk from Africa to South America?

Some truly revolutionary scientific theories may take years or decades to be accepted. This is certainly true of plate tectonics, one of the most important and geological theories of all time, which was ridiculed when it was first proposed.

Wegener’s discovery

Alfred Wegener was a German geologist and explorer who first made the important discovery. In the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals found on opposite sides of the Atlantic. At the time it was believed that land bridges, now sunken, had once connected far-flung continents, and this explained the fossils.

However Wegener noticed the close fit between the coastlines of Africa and South America. Not only that, but the Appalachian mountains of North America matched with the Scottish Highlands, and the distinctive rocks of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil. Wegener also found that fossils of tropical plants, such as ferns and cycads, are found today on the Arctic island of Spitsbergen, which would only happen if Spitsbergen had once had a tropical climate.

When the world was united

In 1915 Wegener published his book The Origin of Continents and Oceans, outlining his theory of “continental drift”. He claimed that about 300 million years ago, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or split, and its pieces had been moving away from each other ever since.

Reaction to Wegener's theory was almost uniformly hostile, and often exceptionally harsh and scathing; Dr. Rollin T. Chamberlin of the University of Chicago described Wegener as ‘footloose.’ Part of the problem was that Wegener had no convincing mechanism for how the continents might move.

Proving him right

Wegener died in 1930 while on an expedition in Greenland, with most scientists still rejecting his findings. However the mapping of the ocean floors revealed such structures as the Mid-Atlantic ridge and scientists came to realise that new magma from deep within the Earth rises and eventually erupts along the crest of the ridges to create new oceanic crust. This process operating over many millions of years continues to form new ocean floor all across the 50,000 km-long system of mid-ocean ridge so that by the 1960s it had become accepted that Wenger’s theory was mostly right.

We now know that both continents and ocean floor form solid plates, which "float" on the underlying magma of the Earth’s core. We also know that Pangaea, the supercontinent postulated by Wegener did indeed exist about 250 million years ago, before each of the continents drifted to their current places.

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