<p>This is a very good question. There a few main heat sources: Heat(and work) left over from the formation of the earth, work (potential energy) generated by dense iron sinking into the center of the earth and forming a core, and radioactive energy. Since the Thermal diffusivity of the materials that make up the earth is low, heat transport is very slow and thus the planet retains a significant amount of its heat. </p>

<p>Another reason why the earth is so hot, is that mantle convection is a very inefficient way to transport said heat, and thus the earth loses energy very slowly.</p>

<p>We know how hot the interior of the earth might be because of laboratory experiments, and also volcanic eruptions. How much energy(temperature) does it take to melt gabbro (mantle rock)? </p>

<p>Interestingly enough, the earth is cooling. And the inner core / outer core boundary is a freezing front (meaning turning from a liquid outer core to a solid inner core). Though, it is a very hot freezing front.</p>

CC BY-SA 3.0
2014-05-03T20:02:11.267Z
"mantle convection is a very efficient way to transport said heat, and thus the earth loses energy very slowly" - shouldn't that sentence include a not?
Siv
CC BY-SA 3.0
2014-04-16T06:00:39.360Z
Will the hot inner-core eventually conduct heat to the crust, increasing surface temperature of the Earth?
Kenshin
CC BY-SA 3.0
2014-04-16T06:03:19.013Z
Sort of; Heat is definitely transported from the inner core all the way to the crust. Thats what drives mantle convection and plate tectonics. But because it is transporting said heat (moving hot rock all the way up to the surface) it loses a lot of energy. Most of the surface heat comes from the sun, as the lithosphere ( more notable than and different than the crust) acts as an insulator for the planets interior, turning it into an oven.
Neo
CC BY-SA 3.0
2014-04-16T06:09:26.447Z
@Mew Actually it does continuously, until a thermodynamical equilibrium is reached, but the continuous heat transport is the reason why geothermal heating systems work.
hugovdberg
CC BY-SA 3.0
2014-04-17T06:51:55.773Z
This answer left me wanting, so I asked [how is heat transferred from the core to the crust?](http://earthscience.stackexchange.com/questions/258/how-is-heat-is-trasferred-from-the-core-to-the-crust)
naught101
CC BY-SA 3.0
2014-04-16T05:58:50.457Z
2014-05-03T22:42:40.900Z
2014-05-03T22:42:40.900Z
Neo
<p>I have heard that the Earth is made up of four layers, being the crust, the mantle, the outer core and the inner core.  I have also heard that the Earth's temperature increases as you move from the crust to the inner core, with the inner core having a temperature of 4700 degrees.</p>

<p>Why is it that the inside of the Earth is so hot compared to the outside of the Earth?</p>

<geophysics><temperature><geothermal-heat>
Why is the inside of the Earth so hot?
Kenshin
# Why is the inside of the Earth so hot?

(Asked by: username_0 on 2014-04-16)

I have heard that the Earth is made up of four layers, being the crust, the mantle, the outer core and the inner core. I have also heard that the Earth's temperature increases as you move from the crust to the inner core, with the inner core having a temperature of 4700 degrees.

Why is it that the inside of the Earth is so hot compared to the outside of the Earth?

**Tags:** geophysics, temperature, geothermal-heat


---

## 1 answers

### Answer by username_1 on 2014-04-16. Score: 13 | Accepted answer

This is a very good question. There a few main heat sources: Heat(and work) left over from the formation of the earth, work (potential energy) generated by dense iron sinking into the center of the earth and forming a core, and radioactive energy. Since the Thermal diffusivity of the materials that make up the earth is low, heat transport is very slow and thus the planet retains a significant amount of its heat.

Another reason why the earth is so hot, is that mantle convection is a very inefficient way to transport said heat, and thus the earth loses energy very slowly.

We know how hot the interior of the earth might be because of laboratory experiments, and also volcanic eruptions. How much energy(temperature) does it take to melt gabbro (mantle rock)?

Interestingly enough, the earth is cooling. And the inner core / outer core boundary is a freezing front (meaning turning from a liquid outer core to a solid inner core). Though, it is a very hot freezing front.

> **Comments:**
> **username_0**: Will the hot inner-core eventually conduct heat to the crust, increasing surface temperature of the Earth?  
> **username_1**: Sort of; Heat is definitely transported from the inner core all the way to the crust. Thats what drives mantle convection and plate tectonics. But because it is transporting said heat (moving hot rock all the way up to the surface) it loses a lot of energy. Most of the surface heat comes from the sun, as the lithosphere ( more notable than and different than the crust) acts as an insulator for the planets interior, turning it into an oven.  
> **username_3**: @Mew Actually it does continuously, until a thermodynamical equilibrium is reached, but the continuous heat transport is the reason why geothermal heating systems work.  
> **username_4**: This answer left me wanting, so I asked [how is heat transferred from the core to the crust?](http://earthscience.stackexchange.com/questions/258/how-is-heat-is-trasferred-from-the-core-to-the-crust)  
> **username_2**: "mantle convection is a very efficient way to transport said heat, and thus the earth loses energy very slowly" - shouldn't that sentence include a not?  

---

