Gold is a naturally forming and naturally occurring element. Scientists at the University of Bristol have recently discovered compelling evidence that most of Earth’s mineable gold is the result of extensive meteorite impacts 200 million years after the Earth’s formation.
Iron, along with most of Earth’s precious metals, sank to the planet’s center during formation to form the core. However, precious metals are far more abundant in the mantle and crust than expected. The prevailing explanation for this abundance is cosmic bombardment, and there is good evidence that this is the case. By obtaining samples of ancient rock from Greenland, researchers have observed the makeup of the Earth soon after its formation, but prior to major meteorite impacts. Scientists use isotopes — atoms with identical numbers of protons but different masses — to learn about the composition of rocks. Isotopic differences between the Greenland samples and modern-day rocks point to gold’s cosmic origins on Earth.
Hot fluids beneath the Earth’s surface account for most of the planet’s mineable veins of gold. Gold dissolves in the hot fluids, and the liquids deposit the ore in cracks and fissures as they cool or vaporize. It can take millennia for a truly mineable vein to form, and geothermally active regions of the Earth are responsible for some of the most productive gold mines.