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Introduction in Plate Tectonics and the theory of Alfred Wegener (continental drift)

More than 100 years ago Alfred Wegener realized that the different continents fit exactly together. This is particularly visible in South America and Africa. Also, the same fossils of plants and animals were found on different continents. Because this is only possible if the plates used to be part of one supercontinent, he thought the plates had moved apart. The theory that plates can move is called plate tectonics. Because no one could imagine that there is a force large enough to move continents, his theory was rejected. About 50 years later, the scientific methods were much more advanced. It became possible to  measure that the seabed was much younger in the middle of the ocean. This seabed was therefore newly added, which ment that the continents moved apart. When this became known, the theory of plate tectonics was accepted in a short time. The supercontinent that existed 250 million years ago when all the plates were stuck together called Wegener Pangea. Pan means whole, while gea stands for the earth. This continent lived up to its name, because it consisted of all the land. If the plates move, there are areas where some plates are separated. These are called divergent zones. There are also areas where plates move towards each other. These are called convergent zones. Finally, there are areas where plates move past each other in opposite direction. These are called transformed zones. The plate boundaries are easy to recognize, because these are the places where earthquakes and volcanoes occur. The plates were able to move because the interior of the earth is very hot. This rock is called magma. Because it’s hot, the magma can flow a little, causing plates to break and move. Although it is often thought that the flowing magma is the driving force for the plate tectonics, it has been found that in divergent zones there are forces that push plates apart and in convergent zones forces that pull the plates towards the convergent zone. These forces are much stronger and therefore they are the cause of the plate tectonics. The plates move very slowly. It usually concerns 1 to 3 centimeters per year. This means that we hardly see a change in the appearance of the earth in a lifetime. But in millions of years, those few centimeters per year suddenly mean a lot. If plates move apart by 1 cm per year for 100 million years, then they are 100 million centimeters further apart, which is 1000 kilometers. The following videos explain more about plate tectonics.