8. Iron, oxygen, and silicon comprise the Earth — mostly.
To better understand the Earth’s components, you should also understand the basics of the Earth’s layers. The ocean basins and continents make up the ‘crust’ layer, which is the Earth’s outermost layer. It varies between three and 46 miles deep. If you could separate the Earth into piles of material, you would have four main components: iron, oxygen, silicon, and magnesium. The majority would be iron at 32.1%; the second would be oxygen at 30.1%. Silicon would come in third at 15.1%, and lastly, magnesium at 13.9%.
However, most of this iron is located at the ‘core’ of the Earth, which is the innermost layer. The core has two parts: a solid inner core and a liquid outer core. The inner core rotates at a different speed than the rest of the Earth. If you could get down and truly sample the Earth’s core, it would be 88% iron. On the other hand, if you tested the Earth’s crust, you would find that 47% of it is oxygen. The ‘mantle’ is between the crust and the core. It is about 1800 miles deep and is mostly composed of magnesium and iron. When this mantle layer is pushed through the crust, we experience volcanoes.