Question

How hot is each layer of the earth?

Answer 1

Hint: Recall that the earth consists of an outermost crust made up of rocks and minerals, the mantle made up of silicate rocks, and the outer and inner cores made up of iron and nickel in liquid and solid-like states respectively. In such a case, determine the temperatures at which the different layers can maintain their respective states of matter to arrive at how hot each layer is. Account for the increasing pressure and density with depth as well.

Complete answer:
We know that the internal structure of the earth consists of concentric spherical layers subdividing the solid Earth. It consists of an outer silicate solid crust, a solid mantle, a liquid outer core and a solid inner core. Each layer has a unique chemical and geological composition, based on which they have different ranges of temperature.
The crust is the outermost layer of the planet consisting of cooled and hardened rocks, that ranges through a depth of $5 – 70\;km$. Owing to the relatively cool rock formations constituting this layer, the temperature of this layer ranges from $0 – 700\;^{\circ} C$ .
The mantle is predominantly solid but behaves as a very viscous fluid in geological time. Its depth ranges from $7 – 2900\;km$ based on the thickness of the crust. The fluid behaviour of the mantle is by virtue of its temperatures ranging from $900 – 4400\;^{\circ}C$.
The outer core, composed of iron, nickel and other lighter elements is about $2300\;km$ thick. This layer is not under enough pressure to be solid, so it is liquid even though its composition is similar to that of the inner core. Thus, the temperature of this layer ranges from $4400 – 5500\;^{\circ} C$.
The inner core has a radius of about $1220\;km$ and is composed mainly of iron and nickel maintained at temperatures around $5200\;^{\circ}C$. The density of this core is very high and is subject to extreme pressures due to which it retains a solid.
Thus, the temperature mostly increases with depth through the structural layers of the earth.

Note:
Note that the temperature of the inner core is far above the melting point of iron. However, unlike the outer core, the inner core is not even liquid or molten. The pressure on the inner core due to the layers around it and the earth’s atmosphere prevents the iron from melting since the pressure and density are simply too great for the iron atoms to disperse into liquid state. Thus, the appropriate way to classify the state of matter in the inner core would be to call it a plasma behaving as a solid.