'Rocks don't lie'
2005-10-28 08:28
The devastating earthquake that killed probably more than 30 000 people in northern Pakistan, India, and Afghanistan last weekend, again confirmed the theory of one of the greatest scientists who ever lived.
Alfred Wegener (1880-1930) formulated the theory of continental drift but was never taken seriously by most of his peers.
Wegener's masterpiece, Die Entstehung der Kontinente und Ozeane, was published in 1912 and when it appeared as Origin of Continents and Oceans in an English translation 12 years later, geologists the world over rejected his theory that there originally was only one continent.
Wegener called this land mass Pangaea which he said had started breaking up into different parts in the Late Carboniferous period nearly 290 million years ago.
He theorised that the present continents' profiles clearly fit into each other like a jigsaw puzzle: the northwestern coast of Africa snugged up perfectly to the east coast of South America; Africa and India were once joined, and Madagascar was also once part of the east coast of Africa.
Wegener emphasised that the supercontinent Pangaea later broke up into two subparts: Gondwana and Laurasia. Gondwana included the present South America, India, Australia, and Antarctic parts, and Laurasia most of the present northern hemisphere subcontinents. Over millions of years, the breakup led to new continents and oceans.
When Wegener died a freezing death in isolated Greenland where he was busy with meteorological research, his theory was in tatters. Yet over the next forty years new technology and research vindicated him when the theory of plate tectonics was formulated.
In 1965 the Canadian geophysicist John Tuzo Wilson set out the theory to explain how the continents drifted apart and how the seafloor is spreading.
Plate tectonics
According to plate tectonics, the earth's outermost layer, the lithosphere, consists of a jigsaw puzzle of rigid plates that "move relative to each other, probably under the influence of convection currents in the mantle beneath," as Scientific American's Science Desk Reference explains it.
"At the margins of the plates, where they collide or move apart, major landforms such as mountains, volcanoes, ocean trenches, and mid-ocean ridges are created. The rate of plate movement is at most 15 cm/6 inches per year."
The tectonic plates of the earth are approximately 100km thick and at least 200km accross. When these plates move towards each other, it can create major earthquakes.
The movement of the continents also lead to the Earth's crust crumbling to form mountain ranges, of which the best example is the Himalayas in Asia which is still being formed because of the northward movement of the Indian subcontinent into the rest of Asia.
Another example is the way in which Africa's northward push into Europe is forming the Alps. The British geophysicist Richard Fortey illustrates this aptly in his brilliant book, The Earth - An Intimate History: "The Matterhorn, on the border between Valais (Switzerland) and Piedmont (Italy) ... its upper portion is actually a part of 'Africa' thrust bodily northwards over Europe."
When the tsunami struck Southeast Asia last December, causing the death of more than 300 000 people, it was the result of the sliding of the India tectonic plate under the section called the Burma plate in the deep sea near the island of Sumatra.
The earthquake in the early hours of the morning last Saturday was along the fault line where the Indo-Australian and the Eurasian tectonic plates collide, pushing up the Himalayan mountain range.
The Indo-Australian plate drives northwards at a rate of a few centimetres per year, pushing under the Eurasian plate and creating a zone that is prone to seismic activity, the New Scientist reported.
Another vindication for observable science and, indirectly, for Wegener's theory. And as Fortey points out, "Rocks do not lie... We know that it is not faith that moves mountains; it is tectonics."
George Claassen is science editor of Die Burger in Cape Town and teaches science journalism at the University of Stellenbosch.
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