Summary

The Earth started as a ball of molten rock and has been cooling ever since. Although the crust has cooled enough for us to live on it, the mantle and core are still very hot. Radioactivity and convection move heat from Earth’s core and mantle toward Earth’s surface. This is why mines can get very hot.

Why watch this video?

Would you like to know how the layers of the Earth keep it warm?

Have you ever been confused by why it’s warmer underground than it is above ground on a sunny day?

Have you ever wondered why miners are always so sweaty?

Key terms

Mantle – the rocky layer between Earth’s crust and core. It is mostly solid rock, but can flow over long timescales.

Convection – when hot rock rises from the boundary between the core and mantle, then once it nears Earth’s outer layers, it cools and sinks back down again. This moves heat throughout Earth’s interior.

Radioactive decay – when an atom’s nucleus breaks apart, releasing energy. This is a source of heat within Earth’s interior.

Loose ends

• The video doesn’t directly address the title; so, why exactly is it hotter underground? As you dig deeper into the Earth, you are gradually getting closer to the mantle. Because the mantle is so hot, we can feel its heat even from kilometers away!
• Why does radioactive decay happen? Radioactive decay happens when there is an unstable number of neutrons and protons in the nucleus of the atom. The atom breaks apart, getting rid of unwanted particles, to stabilize itself.
• How hot are the mantle and core of the Earth? The temperature of the mantle ranges from 500 to 4000 °C, and the core is about 6000 °C.

Self-Test Questions