With the death of the first stars in the form of supernovae, the first metals, such as iron, are formed. However, the formation of heavier metals, such as copper and gold, requires billions of years and further generations of stars. The first generation of stars appears to be Population III, completely devoid of metals. Then, from their debris, Population II forms, already containing iron, albeit in small quantities. Then, in the outer layers of red giants, iron atoms become enriched with neutrons, which then decay into protons, giving rise to elements heavier than iron, such as copper. Finally, with the collision of neutron stars, which releases enormous energy in a fraction of a second (on the order of that emitted by the Sun in its entire 10-billion-year life), heavier elements, such as gold, are formed in enormous quantities: in a 2013 measurement on a supernova, a quantity equal to the mass of the planet Earth was measured. All these elements will then reach Earth and, for the most part, sink to the bottom while it is still liquid, eventually settling in its core. Those we find on the surface are mostly meteoric in nature. The true deposit, however, is the asteroid belt, where billions of asteroids contain precious metals worth several quintillion dollars—about $100 billion for every inhabitant of the planet.
