Structure of the Earth

The structure of the Earth is divided into layers. These layers are both physically and chemically different. The Earth has an outer solid layer called the crust, a highly viscous layer called the mantle, a liquid layer that is the outer part of the core, called the outer core, and a solid center called the inner core. The shape of the earth is an oblate spheroid, because it is slightly flattened at the poles and bulging at the equator.

The boundaries between these layers were discovered by seismographs which showed the way vibrations bounced off the layers during earthquakes. Between the Earth's crust and the mantle is a boundary called the moho. It was the first discovery of a major change in the Earth's structure as one goes deeper.

1. The crust is the outermost layer of the Earth. It is made of solid rocks. It is mostly made of the lighter elements, silicon, oxygen, aluminium. Because of this, it is known as sial (silicon = Si; aluminium = Al) or felsic.
2. The mantle is the layer of the Earth right below the crust. It is made mostly of oxygen, silicon and the heavier element magnesium. It is known as sima (Si for silicon + ma for magnesium) or mafic. The mantle itself is divided into layers.
   1. The uppermost part of the mantle is solid, and forms the base of the crust. It is made of the heavy rock peridotite. The continental and oceanic plates include both the crust proper and this uppermost solid layer of the mantle. Together this mass makes up the lithosphere. The lithosphere plates float on the semi-liquid aesthenosphere below.
   2. Upper aesthenosphere: magma
   3. Lower aesthenosphere
   4. Lower mantle
3. The Earth's core is made of solid iron and nickel, and is at about 5000–6000 °C. which is about the temperature of the photosphere of the Sun.
   1. Outer core is a liquid layer below the mantle.
   2. Inner core is the very center of the Earth.^[1]

A full explanation of these effects is not yet clear. It seems that the high temperature and pressure cause changes in the crystallization of minerals, so that the composition might be a kind of changing mixture of liquid and crystals.

1. ↑ Cite error: The named reference Levin was used but no text was provided for refs named (see the help page).