“What evidence is there to support Alfred Wegener’s theory of continental drift?”
Alfred Wegener, born November 1st 1880, was a German scientist who took a great interest in meteorology and paleoclimatology and in 1905 graduated from the University of Berlin with a Ph.D. in Astronomy. His most notable work was the theory of continental drift. However his theory was highly controversial at the time as he had little evidence, but as technology enhanced neumerous discoveries were made which helped prove his idea of continental drift was true.
In 1912, Wegener published this theory that a single continent existed about 300 million years ago. He named his super-continent Pangaea, and maintained that it had later split into the two continents of Laurasia in the north and Gondwanaland in the south. Today’s continents were formed from further splitting of these two masses. Wegener published this theory of continental drift and claimed that it was supported by several pieces of evidence and that these areas were once joined. Although Abriham Ortelius previously proposed the idea of continents ‘drifting’ Wegener had thought it through in greater detail. He started gathering evidence and found that they fell into three categories, geological, biological and climatological. Wegener noticed the way in which continents such as South America and Africa appear to fit’ together, especially when the edge of the continental shelf is used rather than the present coastline, suggesting that they may have once been joined together – this is also known as the ‘jigsaw fit’. The diagram shows the break-up of the super-continent Pangaea, which figured prominently in the theory of continental drift — the forerunner to the theory of plate tectonics.
Wegener also noticed a link between the rock types and geological structures that were seen to be similar on the two sides of the Atlantic. Such as the Appalachian Mountains in North America and the Caledonian Mountains in Scotland which have the same sequence of igneous and sedimentary rocks, suggesting that they were formed at the same time and in the same place. Other evidence Wegener used to help back to his thesis was that there is evidence of glaciations during the late Carboniferous period 290 million years ago, where striations on rocks left from the ice age were found in South America, Antarctica and India further supporting that they must have been formed together then moved apart. Wegener’s biological evidence was found from some fossils such as that of the Mesosaurus, a small freshwater reptile, which can be found in both southwest Africa and Brazil.
Another fossil was of a small fern, Glossopteris, which were found widely across all southern continents, also suggesting that the landmasses were once joined and such creatures and plants lived in the whole combined area. Climatological evidence found referred to coal and oil reserves found in Antarctica that suggests that this area was once in a different climatic zone in order for this process to have occurred. In this diagram it shows Wegeners idea of how the continents must have been together due to the same fossils being found on different continents around the world.
At the time when Wegener proposed his theory he was widely ridiculed for them because he did not have sufficient evidence to completely prove his theory and due to this many scientists didn’t believe him. Also Wegener wasn’t an official geologist, he was a professor who taught at the University of Marburg in Germany, therefore many people did not take him as a reliable source. Moreover, people in society at the time didn’t believe in Wegener’s theories due to religious beliefs in the early 1900’s, believing that god had created the earth in 6 days, so were therefore stubborn to change particularly as the evidence was insufficient. Another reason why Wegener’s theory was not accepted was that Wegener suggested that the mechanism for the movements of the continents was a combination of centrifugal force and the gravitational pull of the moon. Physicists quickly proved these forces were insufficient to move continents and, partly for this reason, the theory was not widely accepted.
At the time little was known about the nature of the sea floor and this made it difficult to explain the movement of the continents. In addition, it could not be explained why continents appeared to be strong enough to plough through ocean basins even though it was the continents themselves that were deformed by folding and faulting. However from the 1940’s onwards, more evidence began to accumulate as more scientists like Holmes began investigating Wegener’s theory more thoroughly. As more scientists began to expose evidence that was not available to Wegener at the time when he presented his theory, it proved that Wegener could have been right. The mid – Atlantic ridge was discovered and later a similar feature in the Pacific Ocean. When examining the ocean crust on either side of the mid – Atlantic ridge, alternating polarity of the rocks that form the ocean crust were discovered suggesting sea – floor spreading was occurring. When the lava cools and solidifies, particles of iron oxide called magnetite, which are formed in the lava and then erupted onto the ocean floor record the Earth’s orientation at the time. Depending on the polarity at the time the iron particles will align themselves in the same direction. Earths polarity reverses every 400,000 years, meaning a series of magnetic ‘stripes’ of rocks align, alternating towards the north and south poles.
The stripped pattern is symmetrical on each side of the mid – Atlantic ridge suggesting that the ocean crust is slowly spreading away. The switching of magnetic fields was measured by magnetometers towed behind ships in the Atlantic Ocean. In 1929, plate tectonics had moved on from Wegener’s theory, Arthur Holmes, a British geologist, introduced a theory of thermal convection, where by a substance is heated causing its density to decrease, then rising until it cools sufficiently to sink again. According to Holmes it was this heating and cooling cycle that caused the continents to move. By 1960 Holmes was more accepted. The relatively new theory of sea-floor spreading was formed in 1961 – 1962. Scientists proposed that sea-floor spreading is caused by mantle convection to explain the movement of the earth’s continents and plate tectonics.
In conclusion, Alfred Wegener had insufficient evidence to support his hypothesis of continental drift when he first published it in 1912. It was based off of patterns that he had noticed, like the continents ‘looked’ like they all could fit together like a jigsaw and that the rock types and geological structures were seen to be similar on the two sides of the Atlantic as they had the same sequence of igneous and sedimentary rocks – this could have just been coincidence and that they were created around the same time. However as time has progressed, so have people’s views and
technology within the world, therefore more and more evidence has been collected which has helped strengthen Wegener’s hypothesis of continental drift. The fact that people’s views have changed which is obvious as Wegener’s theory is now taught in schools from a young age showing that it must be widely accepted. Today’s scientists proposed the idea of mantle convection to explain the movement of the plates and there has been lots of help form the US Scientists as they are the ones who have discovered Palaeomagnetisim that has helped prove that the continents could move over time, which was one of Wegener’s major flaws in his theory.