The first task about internal geology is ‘internal structure of the earth’, this topic explains how our planet is made of different substances that react to stresses in different ways. This topic is basic for understanding later features about internal geology like plate tectonics theory or volcanoes as they involve forces and materials happening inside the earth.

Of course we don’t know how the inside of the earth is because we have visited it, the methods by which we know how the earth is inside will be explained in the next task.

Internal structure of the earth

The main characteristic of the earth’s interior is that it’s layered. We can distinguish these layers according to different features, these can be either chemical or mechanical (how they react).

According to their chemical properties there are five different layers:

  • Crust: it is the thinnest and the outermost layer. It’s solid and made of rocks, we can sort out two types:

–   Oceanic crust: it´s dense and narrow (around 8 km), made of  iron magnesium silicate rocks (mainly basalt) it´s also younger than continental crust.

–   Continental crust: it´s lighter, bigger thicker and older; it’s made of potassium aluminium rocks (mainly granite).

  • Mantle: is the thickest layer of the earth and represents nearly the 80% of the earth’s volume. The mantle is made of semi-solid materials which may remind us of jam when flowing. The main difference between the upper mantle and the lower mantle (usual divisions of the mantle) is that the upper one is more viscous (except for a thin solid part in the uppermost part) and flows more easily than the lower one which is rather stiff (brittle, rigid) because pressure increases as we go deeper inside the earth.
  • Core: it is usually divided in two: the outer core is liquid and is constantly spinning around the rest of the core; and the inner core is solid. Both are very dense but especially the inner one and both are made of the same materials – some metals probably  iron and nickel -, which are radioactive and so constitute the heat source of the earth.

As a result of their mechanical properties we can divide the earth into four layers:

  • Lithosphere: it is the hard and rigid outer layer of the planet. It’s broken up forming moving plates that float over the underlying layer.
  • Asthenosphere: it is a relatively mobile zone composed of hot, semi-solid material, which can flow as fluids. It takes plays a very important paper role in explaining plate tectonics as the convection currents that happen on it are the force moving plates from beneath.
  • Mesosphere: this layer is more rigid and denser than the asthenosphere.
  • Endosphere: it’s the center (British English: centre) of the earth there the core is, it’s usually divided in two: the outer and the inner core. The outer core is liquid because of the high temperatures it‘s exposed to; it’s constantly spinning round the inner core. The inner core is solid and very dense because of the enormous pressures acting on it.
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