In its natural form, it is found deep in the layers of the Earth, where it is carried by water, molten lava and volcanic eruptions and earthquakes. Geologists have found gold in rocks that are 4.5 billion years old. Unlike other metals that form in the Earth's crust, gold comes from space. The stars are mainly composed of helium and hydrogen, which provide light.
Within the core of the star, nuclear fusion produces energy. When the star's life comes to an end, a massive stellar explosion known as a supernova occurs. On Earth, gold finally came to us about 200 million years after the planet formed, when meteorites filled with gold and other metals bombarded its surface. During the formation of the Earth, molten iron sank to its center to form the core.
This took with it the vast majority of the planet's precious metals, such as gold and platinum. In fact, there are enough precious metals in the core to cover the Earth's entire surface with a layer four meters thick. Gold has only one stable isotope, 197Au, which is also its only natural isotope, making gold a mononuclidic and monoisotopic element. In a monetary system known as the gold standard, a given weight of gold was given the name of a monetary unit.
Under this gold standard, anyone could present paper money to the government and demand an equal value of gold in return. Common colored gold alloys include the distinctive eighteen-carat rose gold created by adding copper. The proportion of gold in the alloy is measured in carats (k), with 24 carats (24 k) being pure gold (100%) and the lower carat numbers proportionally lower (18 carats 3 75%). The World Gold Council states that over 190.040 metric tons of gold have been mined throughout history.
Only 10% of the world's consumption of new gold produced goes to industry, but by far the most important industrial use of new gold is the manufacture of corrosion-free electrical connectors in computers and other electrical devices. Gold is the highly efficient conductor that can carry these small currents and remain free of corrosion, which is why electronic products made with gold are very reliable. In the Book of Exodus, the golden calf is a symbol of idolatry, while in the Book of Genesis, Abraham was said to be rich in gold and silver, and Moses was instructed to cover the mercy seat of the Ark of the Covenant with pure gold. Although the gold ion is toxic, the acceptance of metallic gold as a food additive is due to its relative chemical inertness and its resistance to corrosion or transformation into soluble salts (gold compounds) by any known chemical process found in the human body.
Gold also dissolves in mercury, forming amalgam alloys, and since gold simply acts as a solute, it is not a chemical reaction. The city of Johannesburg, located in South Africa, was founded as a result of the Witwatersrand gold rush, which resulted in the discovery of some of the largest natural gold deposits in recorded history. Gold is also used in infrared shielding, the production of colored glass, the coating of gold leaves, and the restoration of teeth.