In the beginning, Earth was hell.

The planet was completely molten, a roiling sea of magma at temperatures of thousands of degrees. Scientists even referenced Hades to name this period: Hadean Earth.

How did it become the green paradise we know today? Well, over about half a billion years, it cooled. And how it cooled has shaped some important traits of Earth to this day. Logically then, scientists are studying what happened.

They use seismic waves from natural earthquakes and man-made explosions to map today’s inner Earth. And they’re using theoretical modeling to study its ancient past, which suggests that Earth cooled like this:

Very hot surface material, in contact with an early atmosphere, began to cool first.

Convection currents carried warmer magma from Earth’s center up toward the surface and forced cooler material back down.

Metals and elements attracted to iron sunk out of the current to form a central iron and nickel core.

The mantle between surface and core began to cool next, while the lowermost mantle remained liquid.

Scientists think this basal magma ocean had strong fluid currents within it, which may have converted kinetic energy into electromagnetic energy. This could have helped start Earth’s geodynamo—which today generates Earth’s magnetic field from its metal core.

But as with all science, this research is ongoing—so expect updates on a future EarthDate.