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Introduction

OUTLINE THE EVIDENCE TO SUPPORT THE THEORIES OF PLATE TECTONICS & CONTINENTAL DRIFT The theory of continental drift is the idea that about 175 million years ago all the continents of the earth were a single giant landmass. Scientists over the years have looked for evidence to support the idea that the land was once joined, and use several points in their investigations. If land once was joined, the rocks should share common characteristics across the original divide. As old as the earth is, there is a probability that the continents have all collided with each other many times. Some scientists believe that the current continents have come together more than once. Plate tectonics is the theory that Earth's outer layer is made up of many different plates, which have moved around the Earths surface throughout its history. The theory explains the how and why mountains were formed, and also volcanoes, and earthquakes, as well as how similar animals could have lived at the same time on what are now widely separated continents. ...read more.

Middle

Wegener's theory of continental drift was dismissed by several scientists as he was not considered a specialist in any of the sciences he had used to develop his theory and he could not explain how solid land masses had managed to change their positions, he was unable to suggest the mechanism for the drift. Since Wegener put forward his theory of continental drift there have been several pieces of new evidence that support his unproven theory. The discovery of the Mid-Atlantic ridge, which is a range of mountains that run the length of the Atlantic Ocean, found by Ewing in 1948 during an investigation of islands in the Atlantic has shown that the mountain range consists of fairly new volcanic rock - not ancient rock as previously presumed. This evidence proves that there is still physical activity of the earth's crust still occurring today. Studies of palaeomagnetism in the 1950's showed that the rocks that were either side of the Mid-Atlantic ridge had small deposits of iron that were aligned along the earth's magnetic field. ...read more.

Conclusion

The continental plates are older, less dense and consist of silica and aluminium. As a result of the convection currents these plates are moved about either towards, away or sideways to other plates resulting in Fold Mountains, volcanoes, earthquakes and other major landforms. Due to the lower density of the continental crust when the continental and oceanic crusts collide the oceanic crust is forced downwards into a subduction zone where the rock is heated and turned back into a semi-molten state, which rejoins the mantle or increases the pressure in the mantle and causes eruptions. This has occurred in the Pacific Ocean around Asia. When plates move apart to form constructive plate boundaries magma from the mantle surfaces and cools to form new rock between the plates forming mid-ocean ridges and volcanoes. Using all the evidence that has been collated over the years has let us contrive a reliable theory which looks at all possible ideas that may have been overlooked it has lead us to complete a detailed model of the earth's surface and the explanations for landforms and major natural hazards i.e. Earthquakes and volcanoes. ...read more.

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