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Origins of Gold: Where does all the Gold come from?
Gold was first discovered and used on earth around the 4th millennium BCE. A few thousand years ago, in Pre-Columbian South America native tribes prized the precious metal for its otherworldly power. They would adorn themselves in the metal before battle believing that it would grant them mystical powers to defeat their enemies. Fast-forward to 1849, the First Gold Rush in California; people from all across America flock to California to stake their claim on this new frontier’s riches. No one was asking how the gold got there; all they were wondering was how to get rich off of it. This paper is to explore the origins of gold; following the different theories as to how it formed in the universe, including the Big Bang theory and neutron star collisions, as well as how this precious metal got to earth.
Every single element, substance (both man-made or of nature), and atom we have today came from the Big Bang 13.7 billion years ago. Astronomers define the Big Bang as the event where all hydrogen came into existence. In the young, early universe all that existed were protons and electrons seen as separate entities, but as the universe began too cool down the protons combined with electrons producing hydrogen, and soon thereafter helium. As the hydrogen and helium amounts increased, they coalesced into massive gas clouds that give rise to the first stars of the early universe. Stars are the mega production factories of the universe. They fuse hydrogen into helium through nuclear fusion in their cores and continue fusing atom to atom to produce the different elements all the way up to Bismuth, number 83 on the periodic table. However, it is only the most massive stars in the universe that can produce these heavier elements; meaning all elements with a higher atomic number than iron no the periodic table. In comparison to our star that weighs approximately 1.989×1030 kilograms, the stars that produce heavier elements weigh anywhere from 8 to 30 times the mass of our sun and can produce all elements including those from iron to uranium.
There are a couple of different processes a star can undergo to produce heavier elements. The first way to produce heavier elements is by means of the s-process, or slow process. This process takes place in the core of massive red giant stars where over thousands of years the star can manufacture elements higher than iron on the periodic table. In the image below, the s-process is diagrammed to show binding energy on the y-axis and the amount of nucleons in the nucleus on the x-axis. The image illustrates that the material has to be extremely dense in order to fuse with other elements. And so, as the material fuses together it produces energy. This energy then expands the star and causes a decrease in density that slows the nuclear reaction. However, as long as fusion of elements lighter than iron takes place, energy will continue to be added to the star. This is one of the major contributors to stars for supernova events to occur.
(Figure 1. Taken from Physics)
The second process that can occur is the r-process. R stands for rapid because it takes only seconds for this process to go from beginning to end. This process is what happens when a star goes supernova, expelling all of its matter into space forming an enormous gas cloud in the area it once occupied. What takes place is, “in the first few
seconds, protons in the atoms created during the star’s life collide with highly energetic
neutrons, fashioning in an instant all the naturally occurring elements heavier than bismuth up to uranium, and even a few short-lived still-heavier elements such as plutonium and californium” (Tyson). The below image demonstrates a very standard form of the r-process where the supernova has taken place and now the protons and neutrons are combining together to form heavier elements.
(Figure 2. Taken from Physics)
(Figure 3. Taken from abyss.uoregon.edu)
To further understand where gold came from one must first examine how gold was formed apart from the Big Bang. The most recent explanation comes from the collision of neutron stars where different elements are fused together under the intense heat and pressure of the collision forming all precious metals including gold, silver, and platinum. “Such collisions occur when both the stars in a binary system separately explode as supernovas, and then collapse into themselves, leaving behind a pair of tightly bound neutron stars. As they circle each other, the stars are gradually pulled together by gravitational forces, until they collide” (Stromberg). During these collisions a black hole is produced that releases a Gamma Ray burst and a small amount of matter that is thrown outward into space, and “because of the way that heavy elements form, gold must have formed too. The total amount of these heavy elements produced was about one percent the mass of the sun no. Gold, in that distribution, is about 10 parts per million—so that comes out to about ten times the mass of the moon in gold alone” (Stromberg).
From Neutron star collisions, scientists have discovered that, “you need a lot of neutrons to throw at some seed nucleus to build it up to something heavy like gold or lead or platinum… And these explosions make a lot of [neutrons] – about 20 Earth-masses of gold [were created] in the June event, according to a back-of-the-envelope calculation by Daniel Kasen, a University of California at Berkeley astrophysicist. Kasen said that comes out to about 100 trillion oil tankers of gold” (Achenbach).
To continue, another explanation comes from stars exploding during either a type one or type two supernova. Type one and two supernovae can be defined as follows:
– Type I supernova: the star gains matter from a nearby neighboring star until a runaway nuclear reaction ignites.
– Type II supernova: the star runs out of fuel and collapses under its own gravity causing a massive explosion.
(Figure 4. The lifecycle of a star.)
Under all the heat and pressure of the supernova, lighter elements are fused together forming the denser precious metals. This method was thought to be the most accurate explanation up to date until the discovery of the neutron star collision. When a star undergoes a type two supernova, it has run out of all of its hydrogen and helium for fusion, however the core is so dense and hot that it begins to fuse carbon and then the heavier elements sink into the core forming concentric layers around it all the while amassing more and more dense elements until it becomes so dense the star collapses under its own gravity and explodes releasing millions of tons of matter, including precious metals like gold, into space. The remnants of the star are what form a neutron star.
It is well known that during the formation of Earth, all the heavy metals sank into the core of the planet where they have been for the past 4 billion years. As the metals sank in to the core, so too did the gold. Which raises the question, where did all our gold come from, should it not be in the core with the rest of the gold? The answer is, it absolutely is, “In fact, there are enough precious metals in the core to cover the entire surface of the Earth with a four metre thick layer” (Willbold), however, scientists have found that about 200 million years after the formation of the earth, the planet was bombarded by a wave of gold rich, meteorites that were then, “stirred into the Earth’s mantle by gigantic convection processes” (Willbold).
(Baehr. Figure 5)
(Kremer. Figure 6.)
Figure 5 shows the formation of earth and then the bombardment of meteorites to the earth’s surface, showing how earth’s gold became displaced across the surface of the planet. Figure 6 was constructed to show the different meteorite impacts on earth from 4.5 billion years ago to 3.5 billion years ago. The impacts progress through time showing the oldest impacts in red to the younger impacts in blue. Scientists named this massive amount of meteorite impacts as the Late Heavy Bombardment, and from this earth acquired all of the gold we see in top most layers of the earth.
To conclude, gold was created at the start of the universe during the big bang and from thereon was manufactured in the cores of dying stars as well as from neutron star collisions. In the early universe, particles floated around separately until the event occurred when gravity started to pull those particles together to form hydrogen and then helium, lithium and beryllium. From then on particles kept combining more and more until stars were born and could produce every other heavy element on the periodic table. Nearly 200 million years after earth was formed, and all the preexisting gold had sunk into the core of the earth, an event called Late Heavy Bombardment occurred where gold rich-asteroids and meteorites crashed onto the surface of the planet distributing gold and other precious metals throughout the surface of earth. Through these processes and natural events is where all the gold comes from.
- Achenbach, Joel. “Origin of Gold Found in Rare Neutron-star Collisions.” The Sydney Morning Herald. 18 July 2013. Web. 30 Nov. 2014. <http://www.smh.com.au/technology/sci-tech/origin-of-gold-found-in-rare-neutronstar-collisions-20130718-2q64n.html>.
- Baehr, Leslie. Impact model of meteorites. Digital image. Business Insider. N.p., 30 July 2014. Web. 12 Dec. 2014. <http://www.businessinsider.com/early-earth-hit-by-600-mile-wide-asteroids-2014-7>.
- Kramer, Miriam. “Earth’s Gold May Come From Collisions of Dead Stars.” Space.com. 17 July 2013. Web. 30 Nov. 2014. <http://www.space.com/21995-gold-origins-neutron-star-collisions.html>.
- Kremer, William. “Does Gold Come from Outer Space?” BBC News. BBC World Service, 18 Sept. 2013. Web. 30 Nov. 2014. <http://www.bbc.com/news/magazine-22904141>.
- Nucleosynthesis. Digital image. Nucleosynthesis. Uoregon, n.d. Web. 12 Dec. 2014. <http://abyss.uoregon.edu/~js/ast123/lectures/lec21.html>.
- Physics. “Why Does the Sun’s (or Other Stars’) Nuclear Reaction Not Use up All Its “fuel” Immediately?” – Physics Stack Exchange. 14 Aug. 2014. Web. 10 Dec. 2014. <http://physics.stackexchange.com/questions/130231/why-does-the-suns-or-other-stars-nuclear-reaction-not-use-up-all-its-fuel>.
- Stromberg, Joseph. “All the Gold in the Universe Could Come From the Collisions of Neutron Stars.” Smithsonian. 16 July 2013. Web. 30 Nov. 2014. <http://www.smithsonianmag.com/science-nature/all-the-gold-in-the-universe-could-come-from-the-collisions-of-neutron-stars-13474145/?no-ist>.
- Tyson, Peter. “The Star In You.” PBS. PBS, 2 Dec. 10. Web. 12 Dec. 2014. <http://www.pbs.org/wgbh/nova/space/star-in-you.html>.
- Willbold, Matthias, Tim Elliott, and Stephen Moorbath. “Where Does All the Gold Come From?” Bristol University. Nature, 7 Sept. 2011. Web. 30 Nov. 2014. <http://www.bris.ac.uk/news/2011/7885.html>.
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