Gold is a chemical element easily recognisable by its metallic yellow colour. It is valuable because of its rarity, corrosion resistance, electrical conductivity, malleability, ductility and beauty.

If you ask people where gold comes from, most of them will tell you that you have to get it from a mine, look for flakes in a stream or extract it from the ocean. However, the true origin of this element predates the formation of the Earth.

How is gold formed? Origins and processes

Scientists believe that all gold on Earth is of extraterrestrial origin. However, there are still two competing theories:

The first is the explosion of massive stars, called supernovas. Consisting of hydrogen, their intrinsic pressure would have eventually triggered a nuclear fusion leading to the formation of metals such as nickel or iron. As this fusion proceeds, the mass and pressure of the supernova diminish: the star collapses in on itself and eventually explodes. The energy released is such that it forms heavier metals such as lead, silver and gold.

The second hypothesis is that gold is the result of a collision of two dead neutron stars, helping the ordinary hydrogen atom to metamorphose into a single pure gold atom. The origin of the gold would then have been almost instantaneous and would have spread throughout our galaxy in the form of dust. All the gold on Earth today would therefore have come from this explosive encounter between two small stars about ten kilometres in diameter but with an incredible mass of about one billion tonnes per cubic centimetre.

Where is the gold?

All the gold found on Earth comes from the debris of dead stars. When the Earth was formed, heavy elements such as iron and gold flowed into the core of the planet. If no other events had occurred, there would probably be no gold on the surface of the Earth. But about 4 billion years ago, the planet was bombarded by asteroid impacts. These impacts would have stirred up the deep layers of the planet and pushed some of the gold into the mantle and crust.

Gold can be found in rock ores. It occurs as flakes, as a pure native element, and with silver in the natural alloy electrum. Erosion frees the gold from other minerals. Because gold is heavy, it sinks and accumulates in river beds and oceans.

Earthquakes also play an important role, as a shifting fault quickly decompresses the mineral-rich water. As the water vaporises, veins of quartz and gold are deposited on the rock surfaces. A similar process occurs in volcanoes.

How much gold is there in the world?

The amount of gold mined from the Earth is a tiny fraction of its total mass. In 2016, the United States Geological Survey (USGS) estimated that 5,726,000,000 troy ounces or 196,320 tonnes had been produced since the dawn of civilisation. About 85% of this gold remains in circulation. Because gold is so dense (19.32 grams per cubic centimetre), it does not take up much space for its mass. In fact, if all the gold mined to date were melted down, it would make a cube about 18 metres square!

Source: www.thoughtco.com