Question

How do we know that the centre of the earth is hot as we have never been down to the core?

Answer 1

The Earth has a crust, mantle, outer core and the inner core with each one getting hotter than the next. How come, over millions and millions of years, the heat that is at the center of the Earth hasn't conducted throughout the planet's material so that the entire planet is one even temperature?

This always bothered me because we all learn that temperature diffuses from high areas to low areas, yet the Earth's center is super hot while if you dig a one foot hole, the ground feels quite cold.

Answer 2

Seismologists interpret data from earthquakes and even simulate seismic activity with air guns and explosions, and their work has shown that the Earth's interior has different layers, some of which are easier for seismic waves to travel through than others. They can even tell us the densities of these layers.