If you could mine Earth's core, you would find enough trapped gold to coat the entire surface of the planet in a solid shell more than a foot and a half thick.
Our planet’s composition is full of bizarre contradictions. What we experience on the surface is a tiny, highly unrepresentative fraction of what is actually beneath our feet.
During Earth's formation, heavy molten iron sank toward the center to create the core. As it sank, it dragged the vast majority of the planet's precious metals—like gold and platinum—down with it. The gold we mine today was actually delivered much later by asteroid impacts. The inner core itself is a solid sphere of iron and nickel with temperatures reaching around 5,400 °C (9,800 °F), making it roughly as hot as the surface of the Sun. It would normally be a boiling liquid, but the crushing pressure—about 3.6 million times standard atmospheric pressure—forces the atoms into a solid state.
Moving upward to the crust, the elements flip in an unexpected way. When people think of oxygen, they think of the atmosphere. But the air we breathe contains a relatively small fraction of Earth's oxygen. By weight, oxygen makes up about 46.6% of the Earth's crust. It is highly reactive and combines with elements like silicon, aluminum, and iron to form solid silicate minerals such as quartz and feldspar. Almost half of the rock beneath your feet is oxidized metal and silicon.
Even deeper beneath the crust, the mantle hides a subterranean "ocean" that dwarfs all surface water. Hundreds of miles down, there is no sloshing liquid ocean, but rather water trapped inside a rare blue mineral called ringwoodite. The extreme pressure and temperature of the mantle's transition zone force this mineral to act like a sponge, locking hydrogen and oxygen atoms within its crystal structure. Geologists estimate that if ringwoodite in the mantle contains just 1% water by weight, it holds up to three times more water than all the oceans on the surface of the Earth combined.