Geology And Geophysics

Alfred Wegener and his Theory of Continental Drift

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Like many scientists over the years, Alfred Wegener died before his controversial assumption was accepted as fact throughout the world. Wegener, who was born in Berlin on November 1, 1880, was known as the most ardent supporter for the Continental Drift Theory. Although he was not the first person to propose such an idea, he presented the most evidence to sustain it, which helped to eventually prove the point.

The Continental Drift Theory is a belief that millions of years ago, there was a single land mass, known as Pangaea (Greek for “all the Earth”), which gradually split into separate continents over the years. This concept was first proposed around 1800 by German naturalist Alexander von Humboldt, when he observed the fact that the coastlines on both sides of the Atlantic Ocean were of similar shapes. Humboldt theorized that perhaps they were joined at one time.

In the mid 1850s, French geographer and scientist Antonio Snider-Pellegrini made another discovery. Identical fossil plants had been found in both North America and Europe. It was Snider-Pellegrini’s belief that this could only have happened if the two continents had previously been connected. His theory was that the separation of the one land mass was due to a catastrophic event, rather than by millions of years of slow movement. He cited the great Flood of the Bible as a possible cause. Frank B. Taylor, of the United States, also had theories about the continents shifting. He believed that some of the world’s mountain ranges were formed by the collision of large land masses.

Alfred Wegener became intrigued by the idea in 1911 after reading a paper about the identical fossils found on different continents. He had also noted that the continents facing the Atlantic looked as though they would fit together like a huge jigsaw puzzle. Wegener began doing his own research on the subject.  He made maps and graphs of the fossil distribution, and discovered that a pathway was indicated where different species of extinct animals lived. These areas amazingly lined up with the exact area on another continent that would have been connected if his theory was correct. He also noted geographical similarities – for example, if the continents were pushed together, the Appalachian Mountains in North America would line up with the Highlands of Scotland. The strata of the Karoo rock formations in South Africa line up with that of rock formations in Santa Catarina, Brazil.

Wegener also found evidence of ancient life in locations that did not make sense, such as fossils of tropical plants on the Arctic island of Spitsbergen, or evidence of previous glaciers on hot African plains. In his mind, the only way this could have happened would be for the land to have been joined. Opponents of his theory claimed that there may have been land bridges at one time, which had since sunk into the ocean. One of the problems Wegener faced in defending the idea was that he could not explain how the movement came to pass. He suggested that centrifugal force from the earth’s rotation and tidal forces from the moon caused chunks of land to “plow” through the earth’s crust, thus rearranging the geography of the land. He did understand that a force that could move an entire continent would be the same type of force that could produce a mountain range, earthquake or volcano.

Wegener died in 1930, while on expedition in Greenland, and his theory was put to rest until the 1950s and 1960s. In the 1950s, scientists were mapping the floors of the North Atlantic and Pacific Oceans with echo sounders. Their discovery of underwater ridges caused by volcanoes, and the variation of the magnetic field under the sea, led to a theory of seafloor spreading. A decade later, oceanographers explored that idea further, along with Wegener’s Continental Drift theory. With more sophisticated equipment, the theory of plate tectonics was introduced.

J. Tuzo Wilson, a Canadian geophysicist, discovered that the Earth’s crust was actually divided into large, rigid segments called plates. The plates float on the asthenosphere, which is an underlying layer of rock. The asthenosphere is under extreme heat and pressure from the magma beneath, and the rocks are actually more of a viscous liquid. With the shift of the liquid rocks, the Earth’s plates could glide into a new position. Although Alfred Wegener’s theory was known as the “Continental” Drift, Wilson’s research showed that the plates also contained oceanic crust, and affected movement of the ocean floor.

Today, the Continental Drift Theory is widely accepted, and the concept provides valuable information for science. Among other things, this information helps seismologists in their study of earthquakes. Using satellite technology and paleomagnetic data, maps can be made of past plate movements, and the speed of current plate movements can be measured.

More about this author: Candy Spilman

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