Evaluate the evidence for the Earths structure & plate tectonic theory

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Evaluate the evidence for the Earth’s structure & plate tectonic theory.

 

The Earth was thought to be to a flat round solid dome, as thought of by biblical scholars. The Earth as a whole is not just a spherical ball, which is of equal density it is weirder than they had ever imagined.

Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material. Our current information comes from studies of the paths and characteristics of earthquake waves travelling through the Earth, as well as from laboratory experiments on surface minerals and rocks at high pressure and temperature. Other important data on the Earth's interior come from geological observation of surface rocks and studies of the Earth's motions in the Solar System, its gravity and magnetic fields, and the flow of heat from inside the Earth. These studies found out the fundamental structure of the Earth; which is divided up into four parts which are:

  • The Core – is approximately the size of Mars & is the densest part of the planet, being made up of rocks rich in iron & nickel.
  • A Semi-Molten Outer - core contains a solid inner core with a temperature of 6,000°C.
  • The Mantle – (it surrounds the core) this is largely composed of silicate rocks rich in iron and magnesium. Apart from the more rigid upper mantle, most of the mantle (asthenosphere) is semi-molten, with temperatures near the core reaching 5,000°C. These high temperatures generate convention currents.
  • The Crust – (the thinnest layer) this has the coolest, least dense rocks. These rocks are high in silicon, oxygen, aluminium, potassium & sodium. There are two types of crust: oceanic crust, mainly basaltic in nature and around 6-10km thick, and continental crust, which is composed of a widely variety of igneous, metamorphic & sedimentary rocks. Continental crust can be as much as 70km thick beneath the world’s major mountain ranges. The crust is separated from the mantle by the Mohorovijic (Moho) discontinuity. Together, the crust and the rigid upper mantle are collectively known as the lithosphere.
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The crust of the earth is not very thick, (refer to figure 1), it is only 5 to 70km thick. Therefore, the knowledge of the crust is far greater & more widely known. As science has improved so has our concept of the Earth, in the late 1960’s, people had begun to notice how the continents either side of the Atlantic Ocean seemed almost to fit together. As the evidence built up it allowed Alfred Wegener to publish his theory in 1912 suggesting that the continents were once all joined together in an ancient supercontinent he called Pangaea. He ...

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