Imagine there’s a huge hot ball hidden inside the Earth. It's floating in an ocean of molten metal. This ball also spins on its axis, but it moves faster than the rest of our planet. This is what the Earth's core looks like. The solid metal ball is the inner core, and it’s 750 miles thick. The outer core is the molten ocean. To reach the edge of it, you would need to dig a tunnel into the Earth that was about 3,700 miles long.

But you would hardly want to go there, because it’s the hottest point on the planet. The core temperature is 11,000 degrees Fahrenheit. Humans have learned to use the heat coming from inside the Earth as a source of energy. If the core ever cooled down and that heat disappeared, this kind of electricity might become very expensive. Phones, computers, the Internet – all these things would cost a lot more. But this would actually be the least of our worries... So what would happen if the Earth's core went cold?

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