As this material rises and spreads, it carries the seafloor along, similar to a conveyor-belt. He described that the oceanic ridges were located above areas of convective upwelling in the mantle. Using the newly discovered facts, Harry Hess quickly came up with the hypothesis of seafloor spreading. As this new crust formed, the two parts of the old crust would be carried in opposite directions.Ģ) Seafloor Spreading- there was a discovery made of the oceanic ridge system that wound its way through all the major oceans. Vine and Matthews explained that as the magma solidified with the existing magnetic field, it would slowly increase in width as more crust formed as a result of the seafloor spreading. Rocks that have the opposite are said to have reverse polarity. Rocks that exhibit the same magnetism as present is said to possess normal polarity. Thus, as the crust moved, and the rocks recorded the magnetic history, it would do the same when the Earth went through its geomagnetic reversal period. Geophysicists were beginning to accept the idea that over periods of hundred of thousands of years, the Earth went through periods of magnetic reversal where the north magnetic pole became the south, and the south the north. Vine-Mathews-Morey hypotheses connected the two hypotheses, seafloor spreading (described next) and geomagnetic reversals. Thus, rock magnetism provides us a record of its direction and distance from the magnetic poles during the time they became magnetized again. As these rocks moved, they still retained their magnetic alignment and are said to possess paleomagnetism.
When they cool, the minerals would become magnetic again and would freeze in the direction of the existing magnetic poles. When heated above a certain point known as the Curie point, the rocks lose their magnetism. These iron-rich rocks are abundant in lava flows of basaltic composition. Certain rocks contain iron-rich minerals, such as magnetite, that allows it to be used as a "fossil compass". You can think of the Earth as having a magnetic bar, with magnetic fields passing through the planet, extending from one magnetic pole to the other. The Earth has a magnetic north and a magnetic south pole. How are the continents moving across the globe?Ībout 20 years after Wegener's death, two new types of evidence appeared to help understand how the Earth worked.ġ) Paleomagnetism- aka fossil magnetism. One very large issue with his hypothesis was that Wegener was unable to provide the mechanism for his continental drift idea. Wegener received much criticisms for his hypothesis. Much of the glacial evidence lies within 30 degrees of the equator. Layers of glacially transported sediments were found in India, South Africa, South America, Australia, and India. For example, the Appalachian Mountain Range extends fluidly from Eastern America to Western Africa, Greenland, British Isle, and into Scandinavia.Ĥ) Paleoclimatic Evidence: As a meteorologist, Wegener was fascinated to learn that ice sheets covered extensive areas of the Southern Hemisphere and India. Wegener learned that these seeds only grew in subpolar climate.ģ) Rock Types and Structural Similarities: Wegener noticed that if you fit the continent puzzle pieces together, mountain rages and rock types continued from one continent to the next. This plant fossil, with large seeds, was found in regions such as Africa, Australia, India, and Antarctica. Another fossil used as an example for the fossil evidence was the glossopteris. In other words, it's remains should be more widely distributed. Wegener thought, if the creature could travel across the vast Atlantic Ocean, then it should also be able to have traveled to various other regions. One type of fossil organism, the reptilian mesosaur, was found in Eastern South America and Africa. While some areas overlap, such as the west coast of middle Africa, the pieces of the continents fit better than some of the scientists expected.Ģ) Fossil Evidence: Wegener learned that identical fossil organisms were found on both Africa and South America. They discovered that you can get a much better approximation of the actual boundary of the continents if you look at their continental shelf as a boundary line.
There are four main evidence for his hypothesis that he came up with:ġ) Puzzle Fit of the Continents: Some scientists argued that it is a very crude fit so they set out to see how the continents fit together. Wegener hypothesized that Pangaea began to split apart during the Mesozoic Era (approximately 200 million years ago). He proposed a hypotheses called Continental Drift to explain this idea. The Theory of Plate Tectonics first begins with the meteorologist and geophysicist, Alfred Wegener. Wegener proposed that all continents were once joined together at one point called Pangaea (Pan=all Gaea=Earth).
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