They say that hot air rises, then why is the Earth's core down below?

Good question. To answer, let's think about why hot air rises. It rises because it's lighter than the other air around it. Now let's think about the molten rock inside the Earth. There are different kinds of minerals in it, and some are heavier than others. Scientists believe that the minerals in the Earth's core are mostly iron. This is heavier than the other minerals, so it falls to the centre, even though it ends up hotter. The lighter minerals rise towards the surface. But if they get too close, they can cool off enough to become solid, and that's what makes the Earth's crust. So, the lightest kinds of rocks float on top, and below them, the molten rock gets heavier and heavier as you go deeper.

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