Every single atom around us, including those in our own bodies, originated in momentous cosmic events that predate the Earth.
We know this because there are only so many ways to make an atom, and they all involve extreme environments like being in the centre of a star.
But the story really begins minutes after the Big Bang. The universe in these moments was a searing fireball of extreme heat and pressure, where trillions of free-floating protons and neutrons fused together to form the first hydrogen and helium atoms. As the universe cooled over the next few million years, they formed enormous gas clouds, from which galaxies and the first stars were made.
Even now, billions of years after the Big Bang, most of the matter in the universe are these original hydrogen and helium clouds.
Hydrogen and helium are like building blocks because these two elements, combined and rearranged, have formed every other type of atom.
This is called ‘nucleosynthesis’, and each element has a slightly different origin story.
Stars are almost always involved in nucleosynthesis. They are born when gravity pulls a region of a hydrogen and helium cloud into a dense ball.
When the ball reaches a certain mass, the internal pressure deep inside the star becomes strong enough to fuse hydrogen and helium together. This releases huge amounts of light and heat energy, which finds its way to the surface and gives the star its shine.
Because the hydrogen and helium have been fused together, they’ve now become new elements like iron, nitrogen, or oxygen which are the star’s waste products.
After billions of years the star will run out of the hydrogen and helium that it uses as fuel, and the waste elements will build up. What happens next depends on how massive the star is.
Stars with 8x the mass of our Sun and smaller are considered to be ‘low mass’ stars. When they die they create a massive explosion called a ‘planetary nebulae’. The blast itself fuses together many atoms, creating lithium, carbon, nitrogen, and other elements in smaller amounts.
Scientists believe that at least 21% of the atoms in our bodies were created in this way.
The core of low mass stars typically survive the explosion. It continues to shine despite having shed the majority of its mass, though it’s small and not very bright. We call these stars ‘white dwarves’.
Stars with more than 8x the mass of the Sun are considered ‘massive’ stars. They tend to blow up in an even bigger explosion called a ‘supernova’, one of the most immense and powerful phenomena in the universe.
If the Sun went supernova, it would appear 1,000,000,000 times brighter on Earth than a hydrogen bomb pressed directly against your eyeball.
It is a cosmic event so powerful and prodigious that we have no frame of reference with which to really understand it. Supernova explosions are visible across entire galaxies and we can often see one every few years through a telescope as a temporary ‘extra’ star in the night sky.
Like planetary nebulae, the explosion fuses atoms together. But due to its size and ferocity, many more elements are created in a supernova. Supernovae give us oxygen, sodium, neon, aluminium, and many more. At least 65% of the atoms in our bodies originate in a supernova.
I feel that statistics like these are among the most incredible in all of science. Who could have predicted that the matter that makes up us is actually star stuff, and the true history of what we are involves such stunning cosmic events.
Massive stars leave behind a tiny ultra-dense core called a ‘neutron star’, compressed by the force of the explosion.
Exploding white dwarves
Many star systems contain two or more stars closely orbiting each other, in addition to their asteroids and planets. These are called ‘binary’ star systems, and if one star is a low mass star, it can create a special type of supernova explosion.
When the low mass star explodes and becomes a white dwarf, it can steal mass from its companion star. If it grows large enough (past the mass of 1.4x our Sun) it will explode all over again in a ‘Type Ia supernova’. This is a unique environment that creates titanium, manganese, nickel, and zinc.
Events like this may seem rare and unlikely, but our galaxy alone contains hundreds of billions of stars; enough for even the most unlikely events to become nearly inevitable.
For these elements to be found on Earth, this must have happened in the distant past in the area near where our Sun formed.
Merging neutron stars
If two companion stars are both massive stars, when they reach the end of their lifecycle to become neutron stars, they may collide. They will be crushed together into an even bigger neutron star, and sometimes into a black hole.
When this happens, spectacularly intense conditions are produced. A magnetic field trillions of times stronger than the Earth’s is created in two to three milliseconds, the gravitational pull is enormous, and a slew of rare elements are fused in the surrounding gas like uranium, plutonium, and gold. More than 90% of all gold in the universe was produced through an incredible event like this.
Cosmic ray fission
When supernovae explode or when neutron stars merge, they emit a form of highly intense electromagnetic radiation into space called ‘cosmic rays’.
They travel at the speed of light and when they encounter something – like a dusty cloud of atoms like carbon, nitrogen, or oxygen, they will collide with them and cleave them in two. From these collisions, we get beryllium, boron, and lithium.
Some atoms (especially big ones) are too unstable to last long in nature. Over periods of time ranging from seconds to millions of years, they emit radiation and decay into smaller elements. We’ve created a number of elements like this, sometimes on purpose and sometimes as waste products of nuclear bombs, nuclear energy, and particle accelerators.
These elements include technetium, used in diagnosing bone cancer, and californium, used in nuclear reactors. Some of these synthetic elements will last for millions of years, and are almost guaranteed to be the final artifacts of human civilisation.
How they got to Earth
Our Sun is what astronomers call a ‘third generation’ star. It and its planets (including the Earth) formed from the remnants of at least two earlier generations of stars.
Our Sun, the planets, and everything on them were formed in just the right place inside of a dusty nebulae, where the remnants of all of these cosmic events were mixed together. Over time they were pulled together by a centre of gravity which became our Sun and the solar system.
On Earth, a special type of chemistry called ‘biology‘ emerged, and discovered how to utilise the many properties of these different types of atoms into an enormous variety of incredible forms, giving rise to the natural world.
The origin of our atoms forms just one chapter of the story of the universe, the most detailed and astonishing creation story ever conceived.