What is the origin of gold?
Yellow like Sun and Moon, revered for its aesthetic and metallurgical properties for
thousands of years, gold is still today one of the most sought-after precious metals.
There’s no question about it — for better or for worse, gold has played a unique role
for humanity. Today we will explore the fascinating history
of a metal that, like and perhaps more than iron, has influenced the destiny of all civilizations
that have followed one another on Earth in recent millennia, trying to answer the question
that most likely you will have asked yourself from time to time: what is the origin of gold?
Why do we find it on our planet?
From the Neolithic of the Middle East to the Bulgarian Necropolis in the 4th millennium,
from the Egyptian pharaohs to the Spanish conquistadors, the allure of gold – its
powerful effect on us – has been consistent and unmistakable. In fact, the Egyptians called
gold “the breath of God”. And it’s not just the ancients that held gold in high esteem.
What myths made gold such a prized commodity and what factual properties still support
it as a precious metal to this very day? First and foremost, what makes a precious
metal is its rarity. Rarer than silver or copper, two other metals mined since antiquity,
its value was proportionately larger. Second, gold has fantastic properties. It does not
tarnish, it’s very easy to work, can be drawn into wire, hammered into thin sheets,
it alloys with many other metals, can be melted and cast into highly detailed shapes, has
a wonderful color and a brilliant luster. All of these properties could be harnessed
since ancient times, like today, just by heating gold nuggets at high temperatures and using
simple tools like hammers or molds. In short, gold is very memorable, so it shouldn’t
come as a surprise that its main use is in jewelry.
Since time immemorial the noble metal’s resplendent luster allows it to be designed
into the world’s most coveted and exquisite jewelry — fit for queens or kings. Today,
most of the gold that is newly mined or recycled is used in the manufacture of jewelry. About
78% of the gold that’s available, as opposed to stored, each year is used for this purpose.
Because gold is highly valued and in very limited supply it has long been used as a
medium of exchange or money. The first known use of gold in transactions dates back over
6000 years. The first gold coins were minted under the
order of King Croesus of Lydia (a region of present-day Turkey) in about 560 BC. Gold
coins were commonly used in transactions up through the early 1900s when paper currency
became a more common form of exchange. The United States once used a “gold standard”
and maintained a stockpile of gold to back every dollar in circulation. Under this gold
standard, any person could present paper currency to the government and demand in exchange an
equal value of gold. Possibly gold’s greatest use to mankind
didn’t become evident until early last century when its fantastic electrical conductivity
properties came to light. Solid state electronic devices use very low voltages and currents
which are easily interrupted by corrosion or tarnish at the contact points. Gold is
a highly efficient conductor that can carry these tiny currents and remain free of corrosion,
which is why electronics made using gold are highly reliable. A small amount of gold is
used in almost every sophisticated electronic device. This includes cell phones, calculators,
personal digital assistants, global positioning system units, and other small electronic devices.
But the gold is able to amaze us with a bunch of other strange features…
So, before trying to explain its origin, here are some curiosities. Enjoy them!
Gold is the only metal that is yellow or "golden." Other metals may develop a yellowish color,
but only after they have oxidized or reacted with other chemicals.
The chemical symbol for gold is Au, from the Latin word aurum, meaning “shining dawn”
and from Aurora, the Roman goddess of the dawn.
Gold is a noble metal. It is relatively unreactive and resists degradation by air, moisture,
or acidic conditions. While acids dissolve most metals, a special mixture of acids called
aqua regia is used to dissolve gold. The atomic number of gold is 79, which means
there are 79 protons in the nucleus of every atom of gold.
The melting point of gold is 1,064°C Gold is extremely ductile. One ounce of gold
can be stretched to a length of 8 km; the resulting wire would be just five microns
wide. Malleability is a measure of how easily a
material can be hammered into thin sheets. Gold is the most malleable element. One ounce
of pure gold (28,35 grams) could be hammered into a single sheet of nine square meters.
A sheet of gold can be made thin enough to be transparent.
Gold is one of the densest metals found on Earth, a cubic meter of gold weighs 19,300
kilograms, far heavier than lead (11340 kg/m³) and not far off the densest metal, Osmium
(22650 kg/m³). It is estimated that 142,000 tons of gold
have been mined throughout history. Over 90 percent of the world’s gold has
been mined since the California Gold Rush. The coffin found in Tutankhamen's tomb contained
around 1.5 tonnes of gold. The average human body contains 0.2 mg of
gold. Gold ranks 75th in order of abundance of the
elements in the Earth's crust. Fort Knox holds 4,600 tonnes of gold.
Today gold price: 57.22 dollars per gram The visors that protected Apollo 11 astronauts
during the first Moon walk, was gold-coated!
It’s cool, isn’t it? But at this point, it is time to answer the
last question: when was the gold we are finding in the earth's crust formed and where did
it come from? Has it always been there? Or has it not?
The topic is really thorny and even today has aspects not well understood. What we know
exactly is this: gold, like all other heavy elements existing in nature, can be formed
only in thermonuclear reactions of extraordinary power. And in nature, there is only one place
capable of this: the atomic furnace inside the stars.
Could this be the origin of gold? Maybe... let's try to understand it by retracing the
whole process of the formation of a star. All the stars start life largely composed
of immense balls of compressed gas, mainly hydrogen, the first element produced after
the 'Big Bang'. Clouds of stellar hydrogen condense to form
a swirling mass and the inward pressure is held in check by the outward pressure of the
compressed gas. The pressure and friction causes incredible
heat, resulting in a nuclear reaction at the center of the mass. Through a complex series
of reactions, the hydrogen ignites and a star is born. Over billions of years, as the hydrogen
is used up, outward pressure falls enough to allow gravity to squeeze the central core
even tighter, causing greater pressure and temperature. At around one billion degrees,
helium atoms are forged. As this element is devoured in the nuclear
furnace, the core continues to contract and increase internal temperatures until the helium
nuclei fuse to form carbon atoms. The process continues until further fusion
reactions lead to oxygen, neon, and other elements materializing. By now the density
of the core is around 50 tonnes per cubic centimeter, compared to the Earth’s average
density of 5.5 grams per cubic centimeter. With a temperature of around two billion degrees,
neon fuels a fusion reaction to form silicon - a major component of Earth. As each new
element is consumed, so the energy return steadily declines and the star changes, not
every ten thousand years or even every year, but first on a monthly, then daily, and finally
an hourly basis. The last stage is reached when the nuclear
reaction produces an iron core - a more stable element without the ability to burn. The core
by now is typically 200 km across and very dense – it’s estimated that a teaspoon
will comprise around a trillion tonnes of matter – six thousand teaspoonfuls (or 30
liters) would weigh as much as the entire mass of Earth.
The star, with little nuclear energy remaining to support its own weight, contracts so forcefully
under gravity that even atoms are overcome. The trillions and trillions of tonnes of material
surrounding the core rushes inwards at tens of thousands of kilometers an hour, colliding
with the now solid core. The resulting shock wave, like nothing seen
on Earth, travels outwards and is accompanied by a burst of neutrinos formed in the dying
moments. The combined energy of the shockwave and neutrinos transform the star’s outer
layers into an intense stellar furnace. It is in this environment that heavy elements
beyond iron are forged in a mad scramble of hyperactive atoms - then the star literally
disintegrates in the form of a supernova. Iron atoms, along with every other element,
are blasted into space in a nuclear holocaust beyond anything imaginable.
The star will shine with the intensity of ten billion of our Suns - at least for a few
days. Fading within weeks, all that remains of the
star is a huge cloud of gas and dust containing the new elements.
From this cloud, which in astronomy is called "nebula", will condense in turn other stars,
called "second generation stars", which will incorporate and recycle all the new elements
bequeathed by the stars that have preceded them.
But - be careful - among the heavy elements in the nebula there will be no trace of gold!
At most, we will find iron! Until a decade ago it was believed instead
that any star massive enough, at the end of its existence as a supernova would be able
to form elements even heavier than iron, such as gold, but soon it was realized that to
succeed would require energy much greater than that developed by a normal supernova
event ... And on August 17, 2017, astronomers had proof
of their theory! Scientists, in fact, have for the first time
seen the collision of two neutron stars in the galaxy NGC 4993, located nearly 130 million
light years from Earth. But the merger of two neutron stars is more
than fireworks. It’s a factory. Using infrared telescopes, astronomers studied
the spectra - the chemical composition of cosmic objects - of the collision and found
that the plume ejected by the merger contained a host of newly formed heavy chemical elements,
including gold, silver, platinum, and others. Scientists estimate the amount of cosmic bling
totals about 10,000 Earth-masses of heavy elements!
The discovery seemed to confirm that neutron star mergers were responsible for the production
of most of the heavy elements found in the universe.
But certainties, even in astronomy last the space of a morning ... and new observations
already suggest that the number of possible collisions between neutron stars has been
greatly overestimated and that it is, therefore, necessary to assume cosmic phenomena even
more energetic to justify the presence in the universe of so much gold.
Whatever the cosmic origin of gold, to fully answer the initial question we still have
to explain its presence on our planet. It is true that it would be enough to say
(as we have already done) that our solar system, Sun, planets, and everything else, was formed
from dust rich in heavy elements left as an inheritance from stars of previous generations...
However, there is a problem. In fact, as you already know, our planet was
formed about 4.5 billion years ago through a process of accretion that lasted millions
of years, made by attracting dust and planetesimals that met in its orbit around the Sun. The
energy released by this incessant supply of matter then began to produce heat, so much
to reduce the young Earth in an agglomeration of molten rock, homogeneous and undifferentiated.
The high temperatures, also fed by the natural radioactivity of the elements present, reached
and exceeded 1500 degrees centigrade, and this state of fluidity led the heavier elements,
such as iron, nickel, and gold, to slowly sink towards the nucleus, separating from
lighter materials, which were pushed to the outer layers.
So, if 4.5 billion years ago heavy elements left the earth's crust to form the metallic
core of our planet, how come iron, nickel, and gold are still in abundance in mines around
the world? The answer is very simple.
After the Earth's crust cooled, solidifying, there was a period, from 4.2 to 3.8 billion
years ago, in which the meteorite bombardment resumed with great intensity, During this
interval, a disproportionately large number of asteroids are theorized to have collided
with the early terrestrial planets in the inner Solar System, including Mercury, Venus,
Earth, and Mars. And it was the "Late Heavy Bombardment", as it was then called, that
brought back to the Earth's surface most of those minerals that our planet had lost earlier!
In short, we are telling you that all the gold we know... from what we wear to what
we use in computers, from the funeral mask of the sarcophagus of Tutankhamen to the ingots
locked up in Fort Knox...In short, all the gold in this world, is something that comes
from the stars, and from asteroids that devastated the Earth four billion years ago.