For millennia mankind has inhabited the third planet from the sun; the planet that supports life and is know to us as Earth. Although there has been life on Earth for quite sometime, it is only in the past few centuries that man has come to learn about what makes up the interior of this planet.
The English scientist, Isaac Newton, can be seen as a pioneer in regards to learning about the Earth's interior, as he 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 a much denser material¹. Our knowledge of what's inside the Earth has improved immensely since Newton's time, but his estimate of the density remains essentially unchanged.
So what is this new knowledge of the Earth's interior?
A round sphere with many layers, all varying in thickness, each having it's own colour and taste ' this is a description of a gob-stopper and also bares a close resemblance to the internal structure of the Earth; a sphere divided into three layers, differing in density, composition, strength, and state.
The densest of these layers is the core, which is composed largely of metallic iron, with small amounts of nickel and other elements². The less dense mantle then covers this layer, being composed of magnesium and iron silicates. The outermost layer is that of the crust, it has the lowest density of all the layers and can be separated further as its thickness varies greatly from place to place, with the difference being distinguished by land and sea and also its composition. For this reason the core is subdivided into the continental crust (average thickness 45km with a granitic composition) and the oceanic crust (average thickness 8km with a basaltic composition)¹. Similarly the core can also be subdivided, but the difference is not one between compositions but one by physical state. The inner...