Earth is hot inside — Earth science, 4–6 years
The ground is cool where we stand, but deeper inside Earth, rock is under great heat and pressure.
The cool surface covers a hot inside
Earth is not the same temperature all the way through. The thin, solid part where we live is called the crust, while deeper rock is much hotter and pressed tightly by the weight above it. We cannot dig to the centre, but hot springs and melted rock give us clues.
Why ask what is underground?
People saw hot water rising from some ground and hot material coming from deep openings, so they wondered whether Earth was warm inside. The question matters because underground heat can change rock and power some natural events. Since no one can see the deep interior, scientists use clues rather than pretending to have a window into it.
A hot spring is a clue
Imagine visiting a hot spring: first, water comes out of the ground warmer than the air. Next, notice that it has travelled through cracks in rocks below the surface. Finally, infer carefully: something underground heated the water. This does not show the exact centre of Earth, but it is evidence that the ground can be hot below.
“The whole Earth is melted”
It is a reasonable mistake because lava and hot springs show that some material below is extremely hot. Yet the surface is solid, and not every deep layer is liquid. Heat and pressure act together, so Earth has different layers with different states and temperatures.
Using heat from underground
In some places, people use underground heat to warm buildings or produce electricity; this is called geothermal energy. Hot water from below can be useful, but it is not available in the same way everywhere. Engineers must check the local rocks and protect water supplies before using it.
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