The Earth geological layers were formed slowly over hundreds of millions of years. This planet is five billion years old. At the beginning, it was a glowing ball of molten rocks and minerals. As it cooled off, the different geological layers were formed amid volcanic eruptions, earthquakes and other natural phenomena. Today, the science of geology has estimated that the Earth has five geological layers:
1) Inner core. It is the innermost layer, which is made up of solid iron. Its thickness (radius) is about 1,300 km (800 miles). The Danish scientist, Inge Lehmann, determined it was solid by studying the seismic waves that are produced by deep earthquake. It has 1.5 % of the planet mass. Although, it is solid, this ball of iron generates heat.
2) Outer core. It consists of liquid iron and has a thickness of 2,200 km (1,367 miles). It is the source of the Earth’s magnetic field, which is vital for man’s orientation when traveling. It constitutes about 30% of the planet mass.
3) Lower mantle. It is composed of silica (quartz, sand, and flint) and a small amount of iron. This layer has a thickness of 2,500 km (1,553 miles). Its main activity is convection, which is the slow movement of subcrustal materials, transferring heat from the outer core to the surface. It has about 55% of the Earth’s mass.
4) Upper mantle. It is formed almost entirely with peridotite, which is a granular, plutonic igneous rock. It has only 13% of the mass of the Earth as it is 350-km thick (217 miles). Its activity is plate tectonics, which cause the continental drift.
5) Crust. It is made up entirely of granite and basalt, which are igneous rocks, which are hundreds of millions of years old. The main geological activity of this layer is earthquake. It is also called lithosphere, with litho– meaning ‘stone’. Different kinds of sediments top off the crust.
Below, a diagram of the Earth layers. From ‘Simple Geology’
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