Mostly it is assumed that gold and other heavy metals were formed inside our planet way back when the Earth was still a mass of molten rock.
But that's not the case. Gold is heavy. So if gold, platinum, tungsten or any of the other ‘heavy metals’ were around before the Earth’s crust solidified, these metals would have sunk through the liquid rock and have vanished deep into the Earth’s core. Instead they are (relatively) abundant in the Earth's crust. So whats the theory here?
Evolution of Gold
We’re all made out of “star stuff”, so gold shouldn't be an exception.
The ancient Aztecs believed gold was in fact “the sweat of the sun”. Though this isn’t true, the phrase is a highly accurate metaphor.
Gold, like most heavy metals, was forged inside stars through a process called nuclear fusion. In the beginning, following the Big Bang, only two elements were formed: hydrogen and helium. A few hundred million years after the Big Bang, the first stars were blazing away with their nuclear fires. These nuclear fires forced lighter elements together to make slightly heavier elements, and these nuclear reactions released a huge amount of energy.
Gradually, these early stars began making elements such as carbon, nitrogen, oxygen — working their way up through the periodic table towards iron. But there was still no gold in the Universe. Once these earlier stars ran out of light elements to burn, they kicked in on the heavier ones.
Finally, as they burnt silicon to make iron, they exploded as a supernova, and for a few short moments, each star would release as much energy as all the regular stars in that galaxy put together. In that cataclysmic explosion, for the first time, atoms of gold were manufactured — and then hurled out into the Universe, along with the other debris from that explosion.
Gold on Earth
On Earth, gold finally reached us some 200 million years after the formation of the planet when meteorites packed with gold and other metals bombarded its surface. During the formation of Earth, molten iron sank to its center to make 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 entire surface of Earth with a four-meter thick layer.
So the heavy metals mined today fell on Earth approximately 3.8 million years ago. That's when the Earth was bombarded with literally billions of tons of material in the course of a massive asteroid shower. There was gold in those asteroids, and they ended up embedded in the ground, just ready for us to mine it.
Another theory concerning the formation of gold that’s been gaining a lot of attraction today is that the element can form following the collision of two neutron stars. Following the collapse of a massive star – at least eight times more massive than the Sun – what remains is a extremely dense core. They have masses comparable to a star, but that mass is compressed into an object roughly 10 kilometers in diameter, or the size of a city on Earth. Another way to look at this would be to imagine cramming Mount Everest into your morning cup of coffee to achieve the same density as a neutron star. At these huge densities, the fabric and space and time is stretched by exotic physics.
Two neutron stars in mutual orbit can collide when gravitational waves carry enough energy away from the system to destabilize the orbit. When this happens, a type of gamma-ray burst can occur – these are the most powerful explosions in the universe. The intense energy would be enough to create gold and other heavy elements, according to a paper published in the Astrophysical Journal.
So the next time you see gold jewels, do remember where it came from..