The Universe-3.
Enumerating the basic building blocks and understanding how they fit together,
is the province of the science of particle physics.
This quest continues at the Large Hadron Collider at CERN in Geneva.
By early 2011 we had discovered that the Universe is composed of 12 building blocks.
Three of them are required to build everything on our planet, including our bodies.
These three components, known as Up and Down quarks and the electron,
can be assembled into the more familiar protons and neutrons.
Two Up quarks and a Down quark make a proton.
Two Down quarks and an Up quark make a neutron.
Protons, neutrons and electrons make up the chemical elements.
94 of these elements, like hydrogen, oxygen, carbon, iron, gold and silver occur naturally.
For thousands of years ancient astronomers endeavoured to catalogue the stars they could see.
The oldest known record of a star chart may be over 30000 years old.
A 30,000 year old carved ivory tusk discovered in Germany in the 1970’s,
appears to be imprinted with the pattern that resembles the constellation of stars,
we now call Orion.
In France, cave paintings reveal that humans were mapping the night sky,
tens of thousands years ago.
The Egyptians were one of the ancient cultures to not only map the night sky,
but to name some of the stars they observed.
They called the North star, the star ‘that cannot perish’.
They also recorded the names of constellations .
The Sumerians and Babylonians went a step further,
by writing down these early names and patterns and creating astronomical catalogues,
that listed and grouped stars, in ever increasing complexity.
Greek, Chinese and Islamic astronomers all continued to build,
more complex systems of classification .
Many stars today are still being referred to their original Arabic names.
To the ancients the stellar back drop had a deceptive permanence,
that motivated them to mythologise the patterns they saw.
In 185 AD, for the first time in recorded history,
a particular type of fleeting addition to the night sky was observed and documented.
Understanding the nature of this rare and spectacular phenomena,
eventually led us beyond merely naming stars, and enabled us to tell the story,
of their births and deaths.
In 2006, the remains of the cosmic event of 185 AD, that illuminated the skies and minds,
of Chinese astronomers 2000 years ago was identified.
A picture was taken of the object RCW 86.
This object thought to be the still glowing remains of a supernova explosion.
Supernovae are the final act in the life of massive stars.
They are colossal explosions in which a single star can shine as brightly as a billion Suns.
RCW 86 is the remains of the 185 AD supernova, the guest star described,
by the Chinese astronomers that glowed brightly in the skies for 8 months,
before fading from the view.
It was around 8000 light years away.
The ancient astronomers didn’t know it at that time, but they had documented,
the first clear evidence that the stars must eventually die.
There are vast stellar nurseries in the Universe, where new stars are born.
These fertile areas of star formation are known as nebulae.
They are among the most beautiful structures in the skies.
One of these, the Orion Nebula, is perhaps the most studied astronomical object.
It was discovered in 1610.
There is evidence from the folk tales that the Mayans knew about the faint smudge,
beneath the stars of the Orion’s belt.
It can been seen with the naked eye on a very dark clear sky.
It is this complex, ever changing formation that has taught us most about how stars are born.
The Omega nebula, is a vast interstellar cloud that is over 15 light years across,
and illuminated by hundreds of bright young stars.
These stars will burn for hundreds of millions or billions of years,
sending a constant stream of light across the sky.
Ultimately the hydrogen in their cores will get depleted,
and force them to expand and transform into giants.
At the end of their lives, the most massive stars are transformed into colossal giants.
One such star is the Red Mira.
Its radius is 400 times that of our Sun.
It is just clinging on to life.
When the end finally comes for stars like these, the ensuing supernova explosion,
will leave only a faint trace of the star.
For the largest stars, the supernova will leave a black hole behind.
A black hole is an object so dense that even light cannot escape its clutches.
Slightly smaller stars will end their post supernova days as neutron stars.
We detect neutron stars by the light house beam of radio waves they emit,
as they spin every few seconds or less.
Stars much smaller than Mira won’t go out with a bang.
Such relatively cool stars are called red dwarfs.
They are the most common type of stars in our galaxy.
Perhaps the most famous of these, we have studied is Gliese 581.
It is just over 20 light years away from Earth.
A light year is 9.5 trillion kilometres.
The star has been the subject of intense observation in recent years,
due to the discovery of at least 6 exoplanets orbiting around it.
More excitingly planet Gliese 581g is thought to orbit within the habitable zone of the star.
It is considered a prime location for extraterrestrial life.
One of the most exciting areas of current astronomical research,
is the hunt for planets around other stars, known as exoplanets.
They are potential homes for extraterrestrial life.
Until recently such a search would have been impossible,
as planets are too faint to see in interstellar distances.
Thanks to modern instrumentation, we are now able to detect them.
We use the telltale signals of exoplanets using two main techniques.
The radial velocity method, and the transit method.
With these techniques, individual planets have been discovered around hundreds of stars.
Masses of these exoplanets range from a few times that of Earth, to the size of 25 Jupiters.
Whether a planet could support life depends on the distance from the parent star.
Around each star is a ‘habitable zone’, in which temperatures are suitable,
for water to exist as liquid.
The size of the zone depends on the energy output of the star.
The smallest ones have the closest, narrowest, zones.
The red dwarf Gliese 581, is believed to have at least one planet within its habitable zone.
As we observe the Cosmic structures, each tells us something different,
about the life cycle of stars.
Stars are the ultimate origin of all but the simplest of atoms.
They are the building blocks of life.
To comprehend how the stars could play such a vital role in our existence,
we need to look at our own Earth.
With over 100 peaks exceeding 7200 metres, the Himalayan range is truly a land of giants.
9 of the 10 highest mountains are part of the Himalayan range.
The greater Himalayan is home to 45 of the World’s top 50 highest peaks.
Despite their majesty, just a few 10’s of millions years ago,
these mountains were something very different.
As well as being the largest mountain range, the Himalaya is one of the youngest.
Just 70 million years ago, the Himalayas did not exist.
The relentless movement of Earth’s tectonic plates shaped these mountains,
in a geological heartbeat.
As the Indo-Australian plate collided with the Eurasian plate,
at the rate of 15 centimetres a year.
The ocean floor in-between began to crumble and rise up to form the mountain range.
This means that much of the rock out of these towering peaks are made,
was formed at the bottom of the ocean.
It was lifted up thousands of metres into the air over a few millions of years.
If you look closely at any piece of Himalayan limestone,
you will see a chalky granular structure.
What you are looking at are the petrified remains of sea creatures.
They are the bodies and shells of coral polyps that died millions of years ago.
Given a relatively short timescale, and some pressure, these biological remains,
are converted into solid rock.
Limestone can also be formed by the direct precipitation of calcium carbonate from water.
However the biological sedimentary form is more abundant.
We know that the Himalayan limestone is predominantly biological,
because we have found fossils at the top of Mount Everest.
There is perhaps no better example of the endless recycling of Earth’s resources,
since the formation of Earth, almost 5 billion years ago.
We humans are also very much part of that system.
Every atom in our body was once part of something else.
It may have made up an ancient tree, or a dinosaur.
It was certainly a part of a rock.
The rocks of Earth can become living things.
Living things will eventually die, and become rocks again.
Everything in the Universe is composed of the same basic ingredients.
The periodic table is a chart, that lists all the chemical elements,
which are the fundamental units of matter.
It was considered to be the basic building blocks of the world.
It wasn’t until 1869, that the Russian chemist Dmitri Mendeleev finally tamed,
the ever expanding list of basic constituents of matter.
Mendeleev’s genius was to arrange the list of then known 66 elements,
into a table according to their chemical properties.
In the process the table provided a neat way of grouping the elements,
according to their properties.
It also predicted the existence of 8 elements, yet to be discovered.
Over the next 36 years all 8 elements were discovered.
This included gallium and germanium which had the exact properties,
predicted by Mendeleev’s table.
The number of elements continued to grow.
The 101th element was discovered in 1955.
It was named Mendelevium as a tribute to the father of the periodic table.
Today 118 elements have been categorised.
The latest is ununseptium, synthesised and detected in 2010.
Starting with hydrogen and ending with plutonium, the first 94 elements of the table,
have been found occurring naturally on Earth.
These elements are nature’s building blocks.
The remaining 24 elements, can only be created artificially,
and live for very short period of time.
Using these 94 elements we can explain all of biology and chemistry,
without knowing the underlying structures of protons, neutrons, electrons and quarks.
We need very high energies and temperatures to break apart the elements,
a condition that exists naturally deep inside the stars.
The first step of our journey to explain where we come from,
is to understand the origin of these 94 elements.
But first we must discover how we know that everything in the Universe,
is made of the same stuff.
On 21st July, 1969, in the Apollo 11 mission, Neil Armstrong and Buzz Aldrin,
became the first humans, to set foot on the moon.
They spent two hours and 36 minutes there.
They drove two core tubes into the lunar surface,
to collect the most famous rock samples in history.
They collected 22kg of lunar treasure.
These rocks continued to be analysed to this day, in the laboratory in Texas
These priceless samples of alien geology,
are remarkably similar to the rocks found on Earth.
They are composed of the common rock forming elements, oxygen, silicon, magnesium,
iron, calcium and aluminium.
There was absolutely nothing new on the moon.
Since Apollo 11’s success, we have landed on Mars and Venus,
parachuted into Jupiter’s atmosphere, touched down on Saturn’s moon Titan,
and visited asteroids Eros and Itokawa, and the comet Tempel 1.
Each time the story is the same: the solar system is made up of the same elements as Earth.
We have landed multiple times in Mars, and explored the planet’s geology in intimate detail.
We now know Mars is rich in Iron, which has oxidised to form the familiar rusty red colour.
The Martian soil is slightly alkaline, and contains elements,
such as magnesium, sodium, and potassium,
We know that Venus’ thick atmosphere is full of sulphur.
Mercury is a large ball of iron, with a thin crust comprised mostly of silicon.
Even at the very edge of the Solar System, billions of kilometres away,
we have discovered that Neptune is rich in organic molecules, such as methane,
found in plenty in Earth.
There are no new elements to discover in the Universe.
This is not surprising.
Long ago Mendeleev’s table revealed that there isn’t any room,
for other light element in nature.
We have discovered the full set.
What about the rest of the Universe?
How universal are the elements across the far reaches of the Cosmos?
Could it be that there are places in the distant Universe,
where the laws of physics are different ?
It may seem impossible to presume that we could ever answer this question directly,
and discover what the stars are made of, because they are so far away.
In fact we knew what the stars are made of,
long before we got our hands on the first piece of lunar rock.
The Sun, the star of our Solar System is 150 million kilometres away.
Beyond that and the nearest known star,
the red dwarf Proxima Centauri is 4 light years away.
This is about 40 trillion kilometres.
We have learnt a lot about Proxima Centauri, since it was discovered in 1915.
It is thought that Proxima Centauri is part of a triple star system,
with its neighbouring binary star system, Alpha Centauri A, and B.
Although it cannot be seen with the naked eye,
we are able to measure its mass and diameter,
and chart its brightness across the last 100 years.
Despite the fact that our only contact with neighbouring stars, or any star,
is the light that has crossed the Universe to reach us, we are being able to go much further,
than merely cataloguing them.
We can measure the precise constituents of any and every visible star.
This is because encoded in the light, is the key to understanding what they are made of.
It is made possible by a particularly beautiful property of the elements.
The story of how we learnt to read the history of stars in their light,
began with a work of Newton in 1670.
In his ‘Theory of colour’, Newton demonstrated that light,
is made up of a spectrum of colours.
With a simple glass prism, we can split the white light of the Sun,
into its colourful components.
150 years later the scientists Joseph von Fraunhofer made the startling discovery,
about the solar spectrum, while calibrating his state of the art telescopic lenses and prisms.
Lying within the solar spectrum, Fraunhofer documented the existence of 574 dark lines.
He was unaware of the significance of the discovery at that time.
Fraunhofer carefully mapped their positions in great detail.
He went on to discover black lines in the light from the moon and planets,
and from other stars.
They are now known as Fraunhofer lines.
Further work by two scientist in the 19th century, Gustav Kirchhoff and Robert Bunsen,
finally gave meaning to the lights.
They surmised correctly that these black spectral lines,
were the finger prints of the chemical elements in the atmosphere of the Sun itself.
Across 150 million kilometres, the light of our Sun,
carried the signature of its constituents to us.
Kirchhoff and Bunsen’s discovery were purely empirical.
They had observed that when gases are heated on Earth,
they do not simply glow like a piece of hot metal.
They give off specific colours.
Interestingly those colours depend only on the chemical composition of the gas,
and not on the temperature.
In particular, each chemical element gives of its own unique set of colours.
The elements strontium for example, burns with a beautiful red colour,
sodium with a deep yellow, and copper with emerald green.
The two scientists also noticed that the missing black lines in the solar spectrum,
corresponded exactly to the glowing colours of the elements.
There are, for example, two black lines in the yellow part of the Sun’s light,
that correspond exactly to the two distinct yellow emission lines of hot sodium vapour.
We will be familiar with this mixture of two very slightly different yellows -
which is the colour of sodium street lights.
Interestingly, Kirchhoff and Bunsen had no idea why the elements behaved in this way.
This didn’t matter if all you wanted to do was to match the signature of elements,
observed on Earth, with the signature of light from the Sun and stars.
It wasn’t until the term of the 20th century,
that an explanation for the strange behaviour of elements was discovered.
The answer lies in quantum mechanics.
The spectrographic work of scientists like Krichhoff and Bunsen,
was a major motivating factor in the development of quantum theory.
Elements emit and absorb light,
when the electrons surrounding their atomic nuclei jump around.
The key insight that lit quantum theory,
was that electrons can’t exists anywhere around a nucleus like planets around the stars.
They are instead placed in specific, very restrictive orbits.
The deep reason for this is that electron do not always behave as point-like particles of matter.
They also exhibit wave like properties.
This severely restrict the ways in which they can be confined around the atomic nucleus.
What happens at a microscopic level, when an atom absorbs some light,
is that an electron jumps to a different more energetic orbit.
It emits light when an electron falls back from a higher to a lower energy orbit.
The difference in energy between the lower orbit, and the higher orbit,
must correspond exactly to the energy of the light observed or emitted.
However quantum theory also stipulates that light should not always be thought off as a wave.
Just like electrons, light can behave as both the wave and a stream of particles.
These particles are known as photons.
Now, photons of a particular energy correspond to a particular colour of light.
Red photons have a lower energy, then yellow photons,
which have a lower energy than blue photons.
Since each element has electrons in unique orbits around the nucleus,
this means that each element will only be able to absorb particular photons,
in order to move its electrons around into higher energy orbits.
Conversely, when the electrons drop from higher to lower energy orbits,
they only emit photons of a particular energy, and therefore a very particular colour.
This is what we see when we observe elements emitting particular colours of light.
We are in a real sense seeing the structure of the atoms themselves.
When we look at a spectrum of light from our Sun, we can see hundreds of Fraunhofer lines.
Each and every one of them corresponds to different element in the solar atmosphere,
which absorbs light as it passes through.
From the sodium in the yellow, through iron, magnesium,
to all the way across to the so-called hydrogen alpha line in the red,
the signatures of each of the elements are encrypted in the solar code,
so by looking at the lines in precise detail, we can work out exactly,
which elements are present in the sun.
This turns out to be 70% hydrogen, 28% helium,
and the remaining 2% is made of other elements.
We can apply this theory not only to the Sun, but for any of the stars we can see in the sky.
This allows us to measure the constituents of their atmosphere with extraordinary accuracy.
These spectrographic investigations of the light from the Cosmos,
have confirmed what our scientific intuition suggested to us.
Where ever we look, we only see the signature of the set of 94 naturally occurring elements,
we have identified on Earth.
It is very clear we are connected in a very real sense to the whole of the Universe,
with 100s of millions of stars across billions of galaxies.
We are intrinsically made of the same stuff.
There is one very simple reason for that: everything in the Universe shares the same origin.
In order to understand where we come from, we have to understand events that happened,
in the first few seconds of the life of the Universe.
When the Universe began it was unimaginably hot and dense.
There was no structure.
There was certainly no matter.
It was exactly the same whichever way you looked at it.
It is a difficult concept to grasp, but we can get some idea of what happened,
to the early Universe,
by looking at the behaviour of one of the most common substances on Earth: water.
High in the Andes mountains, in North Chile, we will find the spectacular El Tatio Geysers.
Erupting at 4200 metres above sea level, this is one of the geological wonders in Earth.
It is not only the largest geysers fields in the world, it is also one of the highest.
In the early morning, the combination of super heated water and freezing cold air,
produces a rare phenomena.
Like all geysers, the boiling delivered to the surface by the geological plumbing,
bursts out and flashes into steam, forming the majestic columns.
But here, because of the high altitude and low temperatures, the steam rapidly condenses,
and returns to its frozen state, covering the ground with sheets of ice.
It is a spectacular sight to see water in all its three phases: liquid, vapour and solid.
It is rapid transformation of water through its three phases, that provides us with an analogy,
to discuss what happened in the very early life of the Universe.
A water molecule is made up of two chemicals elements, oxygen and hydrogen.
Oxygen and hydrogen are symmetric when they are alone and uncombined.
This means that the atoms themselves would look the same,
no matter what angle you viewed it from.
In the language of Physics, this is called rotational symmetry.
A perfect sphere has perfect rotational symmetry, because whichever way you look at it,
or spin it around, it looks exactly the same.
When a oxygen atom combines with 2 hydrogen atoms, to form a water molecule - H2O -,
this rotational symmetry disappears.
This is because the water molecule has a particular shape.
There is an angle of 105 degrees between the hydrogen and oxygen atoms.
A physicists would say that the symmetry is now broken,
because the water molecule has a distinct orientation.
We can break the symmetry of water still further by cooling down all the molecules,
until they stick together and solidify into ice.
The crystals of ice are beautiful and impossibly intricate.
They are full of structure and complexity that completely hides the perfect symmetry,
of the original atoms, and also the simple but different symmetry,
of the water molecules themselves.
The important point here is that all this complexity emerged, when the symmetry was broken.
But we did nothing to the water itself to break the symmetry, other than cooling it down.
It looks like a master sculpture chiselled down beautiful patterns in the ice.
This intricacy and beauty emerged completely spontaneously, out of the building blocks,
that are themselves utterly symmetric.
Physicists called this process spontaneous symmetry breaking.
This is the idea that lies at the heart of our understanding of the early Universe.
Thirteen billion years ago, the Universe began in the event called the Big Bang.
We don’t know why.
We also don’t know why it took the initial form, that it did.
This is one of the unsolved mysteries, that make fundamental physics so exciting.
The first milestone we can speak of in scientific language, is known as the Plank Era.
This is a period that occurred a mind blowing 10 to the power of minus 43 seconds,
after the Big Bang.
This number can be arrived at very simply,
because it is related to the strength of the gravitational force.
It is so incredibly tiny ultimately, because gravity is so weak.
We don’t know the reason for that either!
At that time the four fundamental force of nature, that we know today, gravity,
the strong and weak nuclear forces, an electromagnetism, were one and the same force.
It was a single ‘superforce’.
There was no matter at this stage, only energy and the superforce.
This is what physicists call a very symmetric situation.
As the Universe rapidly expanded and cooled,
it underwent a series of symmetry breaking events.
The first, at the end of the Plank Era, saw gravity separate from the other forces of nature.
And so the perfect symmetry was broken.
10 to the power of minus 36 seconds after the Big Bang,
another symmetry breaking event occurred, which marked the end of the Grand Unification Era.
This saw the strong nuclear force, the force that sticks the quarks together,
inside protons and neutrons, split from the other forces.
At this point, the Universe underwent an astonishingly violent expansion, known as inflation.
It expanded 10 to the power of 26 times, in an unimaginably small space of time,
of 10 to the power of minus 32 seconds.
This was when subatomic particles entered the Universe for the first time.
But they weren't quite what we see today, because none of them had any mass at all.
Up until this point, the story is theoretically well motivated, but experimentally untested.
The next great symmetry breaking event, however,
which occurred 10 to the power of minus 11 seconds after the Big Bang,
is absolutely within our reach.
This is because, you are recreating and observing this era, at CERN’s Large Hadron Collider.
It is called electroweak symmetry breaking.
At this point the final two forces of nature,
electro magnetism and the weak nuclear force are separated.
During this process the sub-atomic building blocks we see today,
the quarks and the electrons, acquired mass.
The most popular theory for this process is known as the Higgs mechanism.
The Higgs particle was recently discovered in the Large Hadron Collider project.
We are now on very firm experimental and theoretical ground.
From this point on we know pretty much exactly what happened, in the Universe,
because we can do experiments at particle accelerators,
to check that we understand the physics.
The emergence of the familiar particles and forces, we see in the Universe today happened,
we believe, as a result of as a series of symmetry breaking events,
which began way back at the end of the Planks era.
The concept of spontaneous symmetry breaking in the early Universe,
is the same as far the transitions from water vapour to liquid water to ice.
Complex patterns emerge without prompting, just as the result of fall in temperature.
These patterns obscure the underlying symmetry of the initial state.
Just as the seemingly infinite complexity of snowflakes,
masks the simple symmetry of oxygen and hydrogen atoms, so the array of forces of nature,
and subatomic particles, we see as the building blocks of the Universe today,
obscures the symmetry of the early Universe.
There is now one final step needed to arrive at the protons and neutrons,
the building blocks of the elements, and the first element themselves.
This began around a millionth of a second after the Big Bang.
This is when the quarks had cooled enough to become glued together,
by the strong nuclear force, to form protons and neutrons.
The simplest element, hydrogen, consists of a single proton.
So after only a millionth of a second, in the life of the Universe, the first chemical element,
made its appearance.
After 3 minutes, the universe was cold enough,
for the protons and neutrons themselves to stick together, to form helium.
With two protons and one or two neutrons in its nucleus,
helium is the second simplest chemical element.
There were also very, very small amounts of lithium with 3 protons, and beryllium.
This is pretty much where the process stopped.
After 3 minutes the Universe had the four distinct forces we known of today-Gravity,
the strong nuclear force, and the weak nuclear force and electromagnetism.
It was composed of 75% hydrogen by mass, and 25% of helium.
Our Understanding of the structure of matter has increased in the last century.
Originally, atoms were thought to be the basic building blocks of life.
Rutherford’s famous diffraction experiment proved that matter consisted mainly of space,
with each atom containing a very small dense nucleus, surrounded by a cloud of electrons.
Further investigation showed that each nucleus was composed of protons and neutrons,
which were composed of up and down quarks.
We have now reached what is believed to be the smallest particles possible.
Scientists have not discovered that all matter is composed of 9 particles,
and 4 forces, plus the Higgs Boson.
The history of the Universe can be split into several phases,
according to the physical conditions that existed at the time.
In the first fraction of a second, the Universe was filled,
with a intensely hot soup of energy and exotic particles.
From this emerged the first protons and neutrons.
They later formed the nuclei of the first atoms, mostly hydrogen and helium.
After the emission of the cosmic microwave background radiation,
400,000 years of the Big Bang, the pace of events became more sedate.
Some of the significant events in the history of the Universe can be summarised as below.
13.7 billion years ago time begins.
Temperature is 10 to the power of 18 degrees centigrade.
10 to the power of minus 43 second- Plank Era,
gravity separates from the other forces of nature.
10 to the power of minus 36 second- grand unification era,
the strong nuclear force splits from other forces.
10 to the power of minus 32 second- Inflation Era, super fast expansion of the Universe,
from the size of an atom to that of a grapefruit.
The Universe becomes a seething soup of quarks, electrons and other particles.
10 to the power of minus 11 second- electroweak symmetry breaking occurs.
The electroweak force is split into the electromagnetic force, and the weak nuclear force.
One micro second-Universe has cooled down to 10 trillion degrees centigrade.
This allows quarks to combine and form protons and neutrons.
One second- neutrons gradually convert into protons.
Helium nuclei begin to form, but it is still too hot at 10 billion degrees,
and energetic for atoms to form.
Charged electrons and protons create a dense fog.
400,000 years- electrons combine with protons and neutrons, to form atoms,
mostly hydrogen and helium.
Temperature has come down to 2700 degrees.
1 billion years- gravity makes hydrogen and helium gas coalesce to form giant clouds.
They will later become galaxies.
Smaller clumps of gas collapse to form the first stars.
Temperature of the Universe cools down to minus 200 degrees.
13.7 billion years- present day.
Universe has cooled down to minus 270 degrees.
Galaxies cluster together under gravity.
The first stars die and spew heavy elements into space.
These eventually form new stars and planets.
There is a mystery at the heart of science for which, as yet, we have no explanation.
That is the Universe is simple.
Underlying all that astonishing complexity appears to be a magnificent simplicity.
Nowhere is that simplicity more obvious than in the construction of the elements.
Throughout human history the discovery and use of specific elements,
has been intricately linked with the rise of civilisation.
It is believed that copper was mined and crafted by humans 11000 years ago.
The specific characteristics of this metal ushered in the new age of technology,
when the transition from stone tools and weapons, to metal ones.
4000 years later it happened again with iron.
Even today iron mixed with carbon to form alloy steel is the exoskeleton of industrial civilisation.
These two elements played a crucial role in our history,
because of their particular physical characteristics.
Copper was almost certainly the first metal to be used by humans.
It is such a unreactive element, that it is one of the few metals,
that occurs naturally in its peer state.
It is also very soft and malleable, and so relatively easy to work into tools and weapons.
When combined with tin it forms the alloy bronze.
When combined with zinc it forms brass.
Iron is the most abundant element on Earth,
and the fourth most abundant element in the rocks of Earth’s crust.