This all renewed interest in Wegner’s idea of continental drift which morphed into the theory of plate tectonics that proposes the Earth’s crust is broken up into a dozen or so rigid lithospheric slabs or tectonic plates that move relative to each other moving away each other, toward each other or past each other. They suggested that oceanic crust was spreading apart at under water mountain belts, carrying the continents apart through a process they called seafloor spreading. Data detailing things like the ocean bottom topography, oceanic crust age, and magnetism of the seafloor helped Harry Hess and Robert Dietz propose a mechanism that could explain why the continentals appear to have moved. When Did Plate Tectonics Theory Take Hold? It wasn’t until World War II when new data became available, largely due to the search for enemy submarines, that the idea of drifting continents resurfaced. Many southern hemisphere geologists thought his observations fit very well but the mechanism part of his theory needed to be reworked. Not every scientist thought he was completely off base. Anytime you have a drastic new idea you need good evidence and Wegner did have good evidence but it wasn’t complete. Geologists pointed to the rock strength contradiction – if the ocean crust was so weak that it could be plowed through then why don’t we see buckled and folded oceanic crust – instead we see buckled and folded continental crust forming mountains which wouldn’t make sense if it was so strong that it could plow through oceanic crust. He suggested that tidal forces of the moon and sun were pulling the continents which geophysicists outright did not accept – basically saying it was not physically possible. He suggested that the continents moved by flowing through the crust in the same way that an ice breaker ship would force its way through ice. He named it Pangea which means “All Earth.” Why Was Continental Drift Not Accepted? Wegner had a lot of evidence but the major flaw in the continental drift hypothesis was the mechanism he proposed. Similar observations were made that connected the other continents as well leading to his hypothesis that all of Earth’s land mass was once joined as one giant land mass. There were fossil assemblages (like a fresh water crocidillian that couldn’t swim across the ocean) that matched across continents and there was also strong evidence of ice movement across continents all supporting the idea that South America and Africa were once joined. He found that there were in fact geologic belts that existed across South America and Africa. What Evidence Supported Continental Drift? Wegner further supported his hypothesis using geologic data, he studied the geology across different continents. With this in mind he thought it could be possible that the continents were moving in the same way since it appeared as though the continents fit together like a puzzle piece. In fact, while these big masses don’t appear to be mobile they can actually move a significant amount over time. As he worked with glaciers he noticed that glaciers can actually move (slowly but move nonetheless). Wegner was a meteorologist who did much of his work in Greenland and specialized in snowfall and ice. However, Wegner was the first to come up with a lot of evidence so we will focus on him. Speculation that continents might have 'drifted' was first put forward by Abraham Ortelius in 1596. Who Discovered Continental Drift? Continental drift hypothesis is widely attributed to Alfred Wegner (1912) even though he wasn’t the only one to come up with this idea independently. The idea of continental drift has since been subsumed by the theory of plate tectonics, which explains that the continents move by riding on plates of the Earth's lithosphere (crust and the upper most part of the mantle). What is Continental Drift Hypothesis? Continental drift is a hypothesis that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed. It helped us understand why these features and processes occur where they do. Plate tectonics is known as a great unifying theory because it brought together many separate observations and it is referred to as a paradigm shift because before plate tectonics geologists knew mountains, volcanoes and earthquakes occurred in some places but not others without really understanding why. Plate tectonics is an extremely efficient theory that explains why the Earth’s crust moves and behaves the way it does. What is Plate Tectonics Theory? To understand how rocks formed in the ocean can end up on mountain tops we have to understand why continents and oceans seem to have mobility.
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