Gold is one of the most sought-after metals in the world, and it has been used for centuries to make jewelry, gold coins, and other valuable items. But how is gold made? And where does it come from? In this article, we will explore how gold is formed in the wider universe and how it came to be on our planet. Learn about geological processes that form gold deposits so you can learn where it's found on Earth.
What is gold made of?
Gold is composed solely of gold atoms, making it a pure substance (or in other words, an Element). It cannot be broken down further into any other substance. At the atomic level, gold has a dense and compact structure. Because its atoms are so tightly packed together, like a bunch of tweens at a K-Pop concert, this results in the characteristic lustrous yellow appearance gold is known for. The physical properties of gold, such as its malleability, ductility, and excellent conductivity, are attributed to this atomic arrangement. Now that we know that Gold is a pure substance all of its own, this leads us to the next question;
How is Gold Formed?
Gold in the universe is formed primarily through the r-process (rapid neutron capture) in supernova nucleosynthesis, and recent insights suggest that significant amounts of gold, alongside other elements heavier than iron, might also be produced during the collision of neutron stars.
Supernova Explosion
When a massive star reaches the end of its life, it explodes. This is called a supernova explosion. This explosion releases an immense amount of energy, causing the outer layers of the star to be hurled out into the universe violently. So great is the energy and force of these explosions, they are known causegravitational waves which cause space and time to compress and distort. The ejected star materials contain newly formed heavy elements, such as iron and gold. Gold is one of the most abundant elements created during a supernova explosion, however it is scattered throughout the universe. Supernovae are responsible for creating many of the elements we see in our universe because Stellar Nucleosynthesis is an ongoing process. Because of this, new quantities of elements are being made all the time.
Neutron Star Collisions
Neutron star collisions play a crucial role in the formation of gold and other heavy elements in the universe. When two neutron stars in a binary system gradually draw closer, their eventual merger releases a vast amount of energy, akin to that of a supernova. This intense energy output during the collision establishes the perfect conditions for the rapid neutron-capture process, or r-process. During this process, the dense environment filled with neutrons enables lighter atoms to capture neutrons quickly and undergo a series of transformations, eventually forming heavier elements, including gold. The observations of such a collision in 2017 confirmed the presence of heavy elements, with estimates suggesting that the amount of gold produced could be several times the mass of Earth. This event not only highlighted the role of neutron star mergers in creating gold but also provided key evidence for understanding the origin of precious metals in the universe.
How does the rapid neutron-capture process work?
This process, also called R-process, involves heavy seed nuclei capturing neutrons more quickly than they can undergo radioactive decay, allowing for the formation of heavier elements like gold.
Stellar Nucleosynthesis
Stellar nucleosynthesis is the process by which elements are created within stars through nuclear fusion reactions. Gold is not formed directly during these reactions, but is believed to be produced during a process called r-process (rapid neutron capture). This occurs when neutron stars explode at the end of their life, or when two collide. The intense energy and heat generated in the explosion lead to the synthesis of heavy elements, including gold, through the rapid capture of neutrons by atomic nuclei. This process is responsible for the creation of most of the elements heavier than iron in our universe. To put it simply, Gold is Born when Stars Die.
Yes, it sounds a bit dramatic and death metal-ish but it's accurate.
Where does the New Gold Go?
Nebula Formation
Some of the freshly made Gold and other elements end up in Nebulas. Nebula formation is a fascinating process. It begins with the mixture of stellar debris, dust, and gas that begins to collapse under the influence of gravity. This gravitational collapse leads to the formation of a nebula, which is a dense cloud of interstellar material. As the nebula continues to contract, it will eventually form new stars and planets from its material. The study of nebulae provides us with valuable insight into how our universe was formed and how it continues to evolve. In short, new stars and planets are partially, made of new elements created when old stars died.
One place it ends up, is inside Stellar Dust and Gas Clouds which are the remnants of supernova explosions that disperse into space, mixing with other interstellar dust and gas clouds. These vast regions of space contain a variety of elements, such as hydrogen, helium, and heavier elements from previous stellar explosions. They also contain precious metals such as gold. These clouds are incredibly important for the formation of new stars and planets, as they provide the raw materials needed for them to form. Without these clouds, our universe would be a much different place.
Proto-star Formation
Within the nebula, regions of higher density continue to collapse, forming proto-stars. These proto-stars are the early stages of star formation, where the gravitational energy is converted into heat, causing the proto-star to become hotter and denser over time. This process continues until the core temperature reaches 10 million degrees Celsius, at which point nuclear fusion begins and a star is born. Gold is one of the elements that can be formed during this process, as it is created when two helium nuclei collide and fuse together. As such, gold can be found in abundance around newly formed stars.
Planetary Accretion
As the proto-star continues to grow, it develops a disk of gas and dust surrounding it, known as a protoplanetary disk. Within this disk, small solid particles collide and stick together through a process called accretion. Over time, these particles accumulate and form larger bodies known as planetesimals. As these planetesimals increase in size, they become more massive and begin to attract more material from the protoplanetary disk. This process is known as planetary accretion and can result in the formation of planets with a wide range of compositions, including those containing gold.
Credit – ALMA (ESO / NAOJ / NRAO) / T. Penque-Carreño (Universidad de Chile), B. Saxton (NRAO)
How Is Gold Formed In The Earth?
Unfortunately, it isn't. Considering the sheer amount of energy required to form elements like gold, new gold cannot be formed on Earth. We now know that almost all the gold that exists on Earth was already here when the planet formed. It, along with all the other heavy metals and elements found within the 'local' cosmic area formed the planets in our solar system over 4.5 billion years ago. It seems that gold is a finite resource, and that once we have mined all the gold out of the Earth that there will be no more left. However, this is unlikely to eventuate, as another prevailing theory about the origins of gold speak to some intergalactic visitors (spoiler alert: not aliens) delivering at least some of the gold deposits present on Earth, which opens up the, albeit remote, possibility that the Earth could get another gold delivery sometime in the future, although considering the violent methods involved, do we really want it?
Earth Formation
The formation of Earth began about 4.5 billion years ago, when the solar system was still a cloud of dust and gas. As gravity pulled the material together, it formed planetesimals which continued to collide and merge until they eventually formed planets. Gold and other heavy elements were already present in these clouds before the formation of our solar system, meaning the Earth was formed from already existing amounts of gold and other elements. The gold found on Earth is thought to be a combination of this early supernova manufactured gold, as well as from asteroid collisions containing gold and other heavy metals. We now mine this very same gold for use in jewelry, gold coins, and other objects.
Can you make gold?
The atomic structure of gold is unique and cannot be replicated through any combination of elements or reactions. Making gold through alchemy has been a dream for many throughout history, but unfortunately it is not something that can be achieved. Alchemy is an ancient practice that aims to transmute base metals into gold through a combination of scientific knowledge and spiritual enlightenment. While alchemy may have led to important scientific discoveries, the quest to make gold remains elusive. Gold has been an important fixture in alchemy due to its value, which is why many alchemists practiced transmutation in the hopes of uncovering its secrets. However, despite centuries of experimentation, we now know that making gold is simply not possible unless you happen to be powering your lab with a neutron star that's about to explode. Ultimately, gold can only be acquired through mining or recycling existing sources.
Where Does Gold Come From?
Some gold on Earth wasn't here when the Earth was born. Asteroid origin theory and Mantle Return theory go some way toward explaining the presence of some of the gold found on Earth.
Asteroid Origin Theory
Approximately 4.6 billion years ago, when the Earth was still in the process of formation, it experienced a period of intense battering, called the Late Heavy Bombardment (leave it to scientists to come up with such creative names). During this time, asteroids and other celestial bodies smashed into the Earth, delivering a wide range of materials, including gold.
The theory proposes that some of these impacting asteroids contained substantial amounts of gold. When they collided with the Earth, the gold and other precious metals were deposited into the planet's crust and mantle.
Geological processes such as plate tectonics, volcanic activity, and erosion have since concentrated and brought gold deposits closer to the surface, where they can be mined.
Evidence supporting this theory includes the similarities between the composition of gold found on Earth and that of certain meteorites, which are believed to be remnants of asteroids. Isotopic studies comparing the composition of gold on Earth and meteorites have shown notable similarities, providing further support for this origin theory.
While the exact contribution of asteroids to our planet's gold content is still under investigation, the theory suggests that these celestial visitors played a significant role in enriching our planet with this precious metal. And yes, in theory, this does mean that there could be gold on the moon.
Mantle Return Theory
According to this theory, gold that was initially concentrated near the Earth's surface was drawn deeper into the Earth through subduction zones.
Subduction zones occur when one tectonic plate slides beneath another, causing material from the subducted plate to sink into the Earth's mantle. It is suggested that during this process, gold-rich fluids and minerals, previously concentrated near the surface, are carried down into the mantle.
Over time, these gold-rich fluids can mix with other molten materials in the mantle and become incorporated into new rock formations. This theory suggests that a significant portion of gold may be stored in the deep mantle rather than being concentrated solely in the crust. Continuing tectonic activity would also bring some of this gold to the surface again.
While direct evidence for the mantle return theory is challenging to obtain due to the inaccessibility of the mantle, studies of volcanic rocks and their geochemical signatures provide support for the transportation of gold and other precious metals into the mantle through subduction processes.
Gold Deposits and Concentration
Gold tends to concentrate in certain geological formations. Hydrothermal activity, erosion, and weathering as well as volcanic activity can all play a role in concentrating gold into veins, placer deposits, or sedimentary rocks. Gold concentration is an important factor when prospecting for gold because it helps identify areas with higher concentrations of gold that are more likely to yield larger amounts of the precious metal. Although there are no guarantees when it comes to finding gold, understanding the process of gold concentration can help increase the chances of success for any prospector.
How Much Gold Is in the World?
It is believed that the total amount of gold in the earth's crust is around 170,000 metric tons. However, the vast majority of this gold is dispersed at low concentrations throughout large volumes of rock, making it economically non-viable to extract.
How Much Gold Remains Unmined?
Mining activities have been ongoing for centuries, and a significant portion of easily accessible and economically viable gold deposits has already been extracted. However, there are still untapped reserves that are potentially recoverable with advancing mining technologies. Some estimates suggest that only about 54,000 metric tons of gold are economically recoverable. These estimates are subject to change as gold is found in new areas, and technology improves, but it is clear that the amount of unmined gold is significantly less than the total gold content that is thought to be in the Earth's crust. This doesn't address gold in the mantle, far below the crust.
Gold on Earth, A Finite Resource
Gold is indeed a finite resource, once it's gone, that's it. Whilst this may seem like a bit of a bum note to end this article on, look on the bright, shiny yellow side, this knowledge does add to the preciousness of this valuable resource. We know where gold deposits exist on the planet, and there's a slim chance of us running out of it anytime soon. We know that gold exists in the mantle and core of the Earth. We have explored the cosmic origins of gold, explosive gold formation, and its role in the formation of the planet we call home. The very creation of this amazing element caused space-time to bend and distort. How cool is that? Now that you know where gold came from and how it came to be with us on Earth, are you a fan?
