When studying plate tectonics the best starting point is examining the structure of the Earth. The Earth is very similar to a peach in its structure. In the centre is a solid core. Surrounding the core is the inner core, then the mantle which is covered by the Earth’s ‘skin’ or crust.
Figure 1. Cross section of the earth (source: Wikipedia)
The inner core is the centre of the Earth and is the hottest part of the earth. It is a solid mass of iron and nickel. The temperature of the core is around 5500°C
The outer core is the layer around the inner core. It is also made up of iron and nickel though it is in liquid form.
The next layer is the mantle. This layer is made up of semi-molten rock, known as magma.
The final layer is the Earth’s crust. This layer is between 0-60km thick.
The are two types of tectonic plates – continental plates and oceanic plates. Continental plates are lighter (less dense) than oceanic plates. Oceanic crust is much younger in geologic age than continental crust. Continental crust is on average thicker than oceanic crust.
Cross section of the Earth illustrating oceanic and continental crust.
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