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Humans have been mining gold and other precious metals for thousands of years, but, unfortunately, the planet’s largest deposits are located far beyond our reach.
How far, exactly? Around 1,800 miles (2,900 km) beneath our feet, in the Earth’s core, a region of immense density, temperature, and pressure. According to geologist Bernard Wood of Australia's Macquarie University, there is an estimated 1.6 quadrillion tons of gold at the center of our planet. That accounts for 99% of the total amount of gold on Earth and is many, many times more gold than has ever been mined. It's enough gold to cover the entire surface of the planet in a layer around 1.5 feet (0.46 m) high.
Billions of years ago, small planetesimals containing gold and other metals collided and coalesced together, helping to form our planet. Yet during a period in Earth’s early history, heavy elements that can dissolve in iron (such as gold, platinum, cobalt, and nickel) were drawn to the core, trapping them there as the crust eventually cooled. By contrast, the gold we find today was deposited more recently by meteorites crashing into the planet. Eventually, geological processes concentrated the precious metals from those meteorites into ore deposits that are accessible by mining.
The treasure way, way, way beneath your feet:
- The gold at the center of the Earth is only about one part per million of the core's overall mass. In terms of precious metals, the core has around six times more platinum than gold.
- Professor Wood arrived at his figures by comparing the Earth’s crust to meteorites akin to the planetesimals that crashed together to form the Earth. Compared to the meteorites, the Earth’s crust is vastly depleted of precious metals that sank to the planet’s core before the surface hardened.
- The earliest examples of humans using gold come from the Varna Necropolis in northeastern Bulgaria. Some of the graves contain gold jewelry and other artifacts that may have been created as early as 4,600 BC.
- Starting from the center of the planet, the Earth’s structure consists of the inner core, the outer core, the mantle, and the crust.