What makes Earth’s core hot? Why isn’t it just a cold blob made up of metal and minerals?
In: Earth Science
Two reasons:
1. Before Earth came together, it was a bunch of rocks far apart. In order to move towards each other, the rocks borrowed motion energy from gravity. When they ran into each other, the motion energy turned into heat energy, just like rubbing your hands together turns motion into heat. Part of the heat in Earth’s core is leftover heat from that process, which is still there because the Earth hasn’t had time to cool down yet. In fact, compasses work because the Earth’s core turns itself into a magnet as it cools. Compasses don’t work on Mars because Mars is smaller, and so has already cooled off enough that its core isn’t partly melted.
2. Rocks have a bit of radioactive stuff in them, and radioactive stuff warms itself up by breaking apart big atoms into smaller ones. Really radioactive stuff like some kinds of plutonium can get hot enough to glow even when it’s in small pieces, but for ordinary rocks the warming is so tiny that you don’t notice it unless you have a whole Earth worth of rocks in one place. Without slightly radioactive rocks warming themselves up, the core would be a lot colder than it is.
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