Most of the atoms in your body are 13.7 billion years old, and being you is just the latest page in the story of their life.

We know for sure that they’ve been inside of stars, and floated suspended in outer space for far longer than our species has been around.

They’ve washed through the chemical cycles of the Earth countless times, which might have included being frozen to the top of a mountain in one eon, to stomping through dense jungles as part of the thigh bone of a brontosaurus in the next.

We can use modern science to see the story of us from its true beginning. Along the way we will discover how we are born from the universe, not seperate, like a wave that emerges from an ocean.

Atoms are the minuscule LEGO blocks of everything we see around us. They make up the cells that make up our bodies, and most atoms will journey around the universe for 10 million billion billion years before they break down. They are practically immortal (with some exceptions).

Though there are different types of atoms (called elements) with slightly different but parallel origin stories, they all begin in the same place; the Big Bang.

To find out where their story starts, the lens we have to use is a field of science called astrochemistry, which is the study of atoms and molecules in the universe.

The Plasma Storm

While the nature of the Big Bang itself remains one of the greatest unsolved mysteries in science, we do have a good grasp on what happened immediately afterwards.

From a microscopic point, the universe erupted outwards in a condition of unimaginable heat and pressure. From the sheer amount of energy coursing through the fabric of reality, the first quarks seared into existence like waves erupting from a turbulent ocean.

Within minutes, quarks joined together to form protons and neutrons. They formed an opaque cloud of plasma so vast that it stretched across the new universe. It rippled with light and electricity, and may have looked something like a combination of being inside a plasma globe and the most intense lightning storm of all time.

The universe passed 240,000 years in this dense, violent plasma storm, a time so long on human timescales that it would have encompassed the entire history of our species.

But the same explosive force of the Big Bang that created the plasma storm kept the universe expanding, and eventually, it started to cool off.

The electricity which rippled through the cloud began to combine with its protons and neutrons to form the transparent gasses hydrogen and helium, and thus the first complete atoms to exist in the universe.

About 60% of the atoms in our bodies are directly descended from this hydrogen and helium.

The plasma storm began to fade and was replaced by this new, transparent cloud, and the universe began to resemble space as we now know it.

Inside a Star

In the cold silence of space, your atoms would have been witness to one of the most sublime visions in the universe: the formation of the Milky Way galaxy through a veil of a nebula.

At this point the remaining 40% of your atoms began to diverge from hydrogen and helium.

They started to feel the pull of gravitation. First subtly and slowly, but soon like a colossal riptide, they were pulled into the gravity well of a still-forming giant star, one of the ancestors of our Sun.

As more material fell into the growing star, the pressure felt by your atoms climbed to over 250 billion times the pressure of our atmosphere. A dull glow began as the star ignited, which soon became a heat and light hotter and brighter than anything we could imagine.

Your atoms spent hundreds of millions of years here, adrift in the ebb and flow of the internal storms of the star.

Some fell deep into the star’s core. Here they were subject to pressure that was extreme compared even to the rest of the star, and in this furnace atoms of hydrogen and helium fused together to become oxygen, carbon, iron and other elements, releasing bursts of heat and light as they merged.

In the present day, the light from the Sun that warms your skin and the flickering of light from the stars at night originates from the same brutal process of fusion.

After three to four million years the giant star began to run out of hydrogen and helium fuel in its core. At the same time, its waste products of oxygen, carbon, and iron began to build up, and its light dimmed.

It erupted in a supernova explosion, a blast so violent that it would have been visible from across the other other side of the Milky Way galaxy, if there was anyone there to see it.

The searing explosion fused other atoms, creating more oxygen and carbon, as well as rarer elements like silicon, chlorine, and sodium.

The shockwave pushed the newly formed elements back into what was left of the original hydrogen and helium cloud, disrupting it and seeding it with countless new atoms.

As the shockwave impacted the surrounding gas, it compressed millions of miles of hydrogen and oxygen together to form icy water.

Disrupted from the blast, the gas cloud began to once again feel the pull of gravitation.

But this time, it was full of ice and new rocky elements, which clumped together and grew larger and larger. From the cloud hundreds of new, smaller stars were forming, and possibly planets too.

This cycle of the birth and death of stars and planets repeated a number of times until eventually, one of the new stars was our Sun.

In the small part of the cloud that our Sun occupied, most of the remaining hydrogen, helium, and now other elements too, were once again captured by gravity and were destined to be set adrift in the internal stellar storms all over again.

But some of the gas and rocks found themselves not being pulled in to the Sun, but held in orbit in a vast ring around it called an ‘accretion disc’.

Over time they collided with each other, forming larger and larger asteroids in a series of impacts until they grew to the size of planets, which were bombarded by asteroids for hundreds of millions of years.

When it ignited, the Sun released a series of immense shockwaves that impacted the new planets and determined the shape of the new ‘solar system’.

It pushed most of the gas outwards, towards the outer planets, where it formed the gas giants Jupiter, Saturn, Neptune, and Uranus.

The heavy, rocky material closest to the Sun was left behind by the shockwave, and it formed the small, rocky planets Mercury, Venus, Earth, and Mars, with a thin remnant of gassy atmosphere for each of them.

One of the main scientific goals of missions sent to the Moon and Mars is to gather and analyse their soil, in order to discover the composition of this accretion disc that formed the planets.

Information like this helps us determine if the conditions on Earth are in some way unique, and if this could account for why there is life here. As it turns out, if there is something unique about the Earth, it’s not the soil.

Over time the asteroid bombardments slowed down, and the atoms that would eventually form you found themselves all in one place; Earth.

Check out the rest of the story of your atoms in Part 2!