Gold is a chemical element easily recognized by its yellow metallic color. It is valuable because of its rarity, resistance to corrosion, electrical conductivity, malleability, ductility, and beauty. If you ask people where gold comes from, most will say you obtain it from a mine, or panned from a stream. However, the true origin of the element predates the formation of the Earth.
All of the gold found on Earth came from the debris of dead stars. As the Earth formed, heavy elements such as iron and gold sank toward the planet’s core. If no other event had occurred, there would be no gold in the Earth’s crust. But, around 4 billion years ago, Earth was bombarded by asteroid impacts. These impacts stirred the deeper layers of the planet and forced some gold into the mantle and crust.
Some gold may be found in rock ores. It make occur as flakes, as the pure native element, and with silver in the natural alloy electrum. Erosion frees the gold from other minerals. Since gold is heavy, it sinks and accumulates in stream beds, alluvial deposits, and the ocean.
Earthquakes play an important role, as a shifting fault rapidly decompresses mineral-rich water. When the water vaporizes, veins of quartz and gold deposit onto rock surfaces. A similar process occurs within volcanoes.
How Much Gold Is in the World?
The amount of gold extracted from the Earth is a tiny fraction of its total mass. In 2016, the United States Geological Survey (USGS) estimated 5,726,000,000 troy ounces or 196,320 U.S. tons had been produced since the dawn of civilization. About 85% of this gold remains in circulation. Because gold is so dense (19.32 grams per cubic centimeter), it does not take up much space for its mass. In fact, if you melted all the gold mined to date, you’d wind up with a cube about 60 feet across!
Nevertheless, gold accounts for a few parts per billion of the mass of the Earth’s crust. While it’s not economically feasible to extract much gold, there are about 1 million tons of gold in the top kilometer of the Earth’s surface. The abundance of gold in the mantle and core is unknown, but it greatly exceeds the amount in the crust.