Earth's Iron Core Exists Because Molten Planet Sorted by Density

What was said

"Earth was once molten. When in the early days of formation, when you're molten and as big as the Earth, gravity will do things to that molten mixture. If you're denser, you will sink to the middle. If you're lighter, you'll float."

Tyson explained that Earth's crust is composed of the third-lightest materials (after gases and water), with all heavy metals like iron and nickel having sunk to the core when the planet was molten. This is why surface rocks are relatively low-density and iron ore must be mined from preserved veins.