Continental Drift on Earth
Continental drift is the movement of the Earth’s continents relative to each other by appearing to drift across the ocean bed.The speculation that continents might have ‘drifted’ was first put forward by Abraham Ortelius in 1596. The concept was independently ( and more fully ) developed by Alfred Wegener in 1912. The theory of continental drift was superseded by the theory of plate tectonics, which builds upon and better explains why the continents move.
Alfred Wegener was the geologist who in 1924 propagated the theory of continental drift which is very much in vogue now. According to this theory, nearly 150 million years ago, there was a single continent on earth known as ‘pangaea’ which broke into several pieces and began to drift apart. North and South America pulled away from Africa and Eurasia and drifted to the west. In between the two continental blocks, America and Africa, the Atlantic basin appeared.
Antarctica, Australia, peninsular India and Madagascar were neatly nested together close to the southern tip of South Africa. Again they drifted to the present position, giving way to Indian Ocean basin. This theory has now been established by the theory of ‘plate tectonics’ that, continents are moving as plateaus, on a semi – liquid surface which supports the continental drift theory.
It wasn’t always the case that people believed in continental drift, German geologist and meteorologist Alfred Wegener’s ( 1 ) theory that parts of the Earth’s crust slowly drift atop a liquid core. He believed 200 million years ago there was once a gigantic supercontinent which he called Pangaea ( “All – earth” ) which slowly moved apart.
Wegener’s theory of continental drift became commonly accepted when the driving forces for continental drift were discovered during the 50s and 60s : The enormous heat in the Earth’s core and Earth’s mantle generates the flow of rocks within the Earth’s mantle, a process similar to the movement of warm water in a cooking pot. This heat – driven mass transport by convection leads not only to plate movement on the Earth’s surface but also to drifting of the continents floating on the plates.
In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth’s crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.
Wegener hypothesized that there was a gigantic supercontinent 200 million years ago, which he named Pangaea, meaning “All – earth”.
Fossil Evidence in Support of the Theory
Fossils of Mesosaurus ( one of the first marine reptiles, even older than the dinosaurs ) were found in both South America and South Africa. These finds, plus the study of sedimentation and the fossil plant Glossopteris in these southern continents led Alexander duToit, a South African scientist, to bolster the idea of the past existence of a supercontinent in the southern hemisphere, Eduard Suess’s Gondwanaland. This lent further support to A. Wegener’s Continental Drift Theory.
The theory of plate tectonics ( meaning “plate structure” ) was developed in the 1960’s. This theory explains the movement of the Earth’s plates ( which has since been documented scientifically ) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and other geologic phenomenon.
The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth’s seismic activity ( volcanos and earthquakes ) occurs at the plate boundaries as they interact.
The top layers of the plates are called the crust. Oceanic crust ( the crust under the oceans ) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.
Earth’s Major Plates :
The current continental and oceanic plates include: the Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plates, Caribbean plate, South American plate, African plate, Arabian plate, and the Antarctic plate. These plates consist of smaller sub – plates.
Since the Earth’s crust solidified billions of years ago, plates of its crust have been drifting all over the globe . The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time ( as the temperature on Earth varies and the poles melt or freeze to varied extents ), covering or exposing different amounts of crust.
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