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The atoms in your body were not always yours. Right now it’s more like you’re borrowing them. Most of them are 13.7 billion years old, made shortly after the Big Bang, and being you is just a single page in their long and incredible story.

If we understood how this happens, we’d be able to see how physically interlinked we are with the rest of the universe.

To do this, we have to look into a field of science called astrochemistry, which is the study of molecules in the universe. It can tell us that your atoms haven’t all come from the same place. This isn’t surprising, as the average person is made of seven octillion atoms. That is a seven followed by twenty-seven zeroes!

We know that about four octillion of them are hydrogen atoms, and we can roughly trace their history. They were made just after the Big Bang and floated in vast, ghostly clouds in interstellar space for billions of years.

In the cold silence of space, they 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.

The remaining three octillion atoms of your body were also in the dust cloud but had a very different experience. Like bubbles caught in a colossal riptide, they were pulled into the gravity well of a still-unborn giant star. This star was not our Sun but was one of its ancestors.

They were pulled into absolute darkness as dust closed around them. As more dust fell into the growing star, the pressure felt by your atoms climbed to over 250 billion times the pressure of our current atmosphere. The darkness gave way to a dull glow as the giant star ignited, which soon became a light brighter than anything we could imagine.

Three octillion of your atoms spent hundreds of millions of years here, or in neighbouring stars just like it, adrift in the ebb and flow of the internal storms of the stars. Some atoms 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 atoms of hydrogen fused together to become helium and other elements, releasing blasts of light.

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

After long eons the giant star ran out of fuel. It had burned through all of its hydrogen and as its light began to dim, other elements like helium were pulled into the core to make carbon and oxygen.

Eventually the star erupted in a supernova explosion, a blast so violent that it can be seen from across a galaxy.

The searing explosion fused other atoms, creating more oxygen and carbon. The resulting shockwave pushed them back into the remnants of the original hydrogen gas cloud, disrupting it and seeding it with new atoms. As its shockwave impacted surrounding gas, it compressed millions of miles of hydrogen and oxygen together to form icy water.

Once again, the gas cloud began to collapse but this time, it was full of ice and new rocky elements, which clumped together and grew larger and larger.

From the dust cloud and the remnants of the giant star, hundreds of new, smaller stars were forming. One of them was our Sun.

Some of the cloud was pulled into the Sun’s gravity well, destined to be captured and 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 star, but held in orbit in a vast ring 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 bombardment by asteroids for hundreds of millions of years.

As it ignited, the Sun released a series of immense shockwaves that impacted the new planets and determined the shape of the new ‘solar system’. They pushed most of the gas 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 atmosphere.

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

Here on Earth, they began to cycle through the air, land, and water. At this point, it’s hard to track exactly where your atoms went, but we do know that they have been very well recycled. They no doubt combined into different molecules and broke down again billions of times, but the atoms themselves never degraded.

Every atom you possess has almost certainly passed through several stars and been part of millions of organisms on its way to becoming you. We are each so atomically numerous and so vigorously recycled at death that a significant number of our atoms β€” up to a billion for each of us, it has been suggested β€” probably once belonged to Shakespeare. A billion more each came from Buddha and Genghis Khan and Beethoven, and any other historical figure you care to name. (The personages have to be historical, apparently, as it takes the atoms some decades to become thoroughly redistributed; however much you may wish it, you are not yet one with Elvis Presley.) So we are all reincarnations β€” though short-lived ones. When we die, our atoms will disassemble and move off to find new uses else-where β€” as part of a leaf or other human being or drop of dew. Atoms themselves, however, go on practically for ever.

Bill BrysonA Short History of Nearly Everything

A handful of your atoms may have been used in one of the very first molecules of DNA.

Others may have been used in one of the mandibles of a five-eyed Opabinia regalis, a tiny three-inch predator during the Cambrian Explosion.

Image credit: Dotted Yeti / Shutterstock

Others may have been part of both the muscle tissue of a Tyrannosaurus, and of its prey.

In the chaos of Earth’s ever changing chemistry, it seems like our seven octillion atoms have truly been everywhere. One thing we know for sure though is that your carbon atoms were very recently part of a plant, probably corn or wheat. It pulled carbon dioxide molecules floating in the air and by using the Sun’s light as a catalyst, the green cells of the plant combined them into a long carbohydrate molecule. You recently ate it as part of bread, corn starch, or sugar.

If you recently drank a glass of water, it has also gone through a monumental process. It’s in a constant cycle of rain and evaporation driven by the heat of the sun, while occasionally getting diverted into the belly of a plant or animal. You might have seen a diagram of the water cycle like the one below in school, but what it doesn’t make clear is the scale of this process. Water is exchanged across the entire surface of the Earth, for billions of years at a time.

Your atoms might have been a wave that pushed Christopher Columbus’ Santa Maria across the the Atlantic, or an avalanche that toppled one of Hannibal’s elephants down the Alps, or part of the iceberg that sank the Titanic.

The water cycle. Image credit: NASA

But the atoms that we have now are not the atoms that we’ll keep. In fact, they are completely replaced once every ten years. Steve Grand in his book Creation: Life and How to Make It points out that because our atoms are in constant flux, we are more like a wave than a permanent thing. He invites us to do a quick thought experiment.

Think of an experience from your childhood β€” something you remember clearly, something you can see, feel, maybe even smell, as if you were really there.

After all, you really were there at the time, weren’t you? How else would you remember it?

But here's the bombshell: You weren’t there.

Not a single atom that is in your body today was there when that event took place.

Matter flows from place to place and momentarily comes together to be you. Whatever you are, therefore, you are not the stuff of which you are made.

If that doesn’t make the hair stand up on the back of your neck, read it again until it does.

Steve GrandCreation: Life and How to Make It

To put it another way, the atoms that comprise your mind and body don’t belong to you; you are just renting them for a few years.

“The very dust that blows along the street

Once whispered to its love that life is sweet.”

Hallam HawksworthThe Adventures of a Grain of Dust

After another 5 billion years of cycling around the Earth, all atoms on the Earth will be scorched by the Sun as it expands into the final stage of its life, a red giant. The Sun’s outer layers will inflate until they engulf Mercury, Venus, and finally the Earth. Any life that has not found a way to leave the Earth by this point will be, in a word, cooked.

The Sun will swell into a red giant, scorching then engulfing the Earth. Image credit: James Gitlin

Eventually like the ancestor stars that preceded it, the Sun will explode, returning new atoms to a cold, dark cloud in space. Then the star cycle begins anew. Hundreds of new stars will form, and your atoms will be split amongst a new set of planets, moons, and maybe new forms of life.

The Sun will explode into a nebula, like countless stars before it

Cosmologists believe that this cycle of death and rebirth of the stars will repeat about one hundred times, before the final star in the universe exhausts all fuel and the galaxies go dark.

What will follow is an era of black holes. All matter including your old atoms will either be consumed by them or flung into deep space from their gravity. After countless ages even the black holes disappear, evaporating into nothing but radiation.

The view from a large asteroid in orbit around a black hole

This is the end of the line of what scientists know what will happen for sure, but there is some speculation about what happens next.

One possibility is that, after any surviving atoms and radiation have spent an eternity travelling through the cold, dark remnants of the universe, they will decay into more basic particles. These particles will fill the universe in a ‘thermal equilibrium’, where every place in the universe is almost as cold as absolute zero, and no further exertion of energy becomes possible. This means no stars, life, or intelligence will be possible. It will remain in this state for all of eternity. This is called the heat death of the universe.

A second, more hopeful possibility is that the expansion of the universe itself slows, and is reversed by the pull of its own gravity. After hundreds of billions of years, every atom and flash of radiation are brought back together until they rush to collapse into a single point. This is a reversal of the Big Bang, called the ‘Big Crunch’.

Many scientists believe that the Big Crunch will be the end of our universe, but it may be followed by something spectacular. A new Big Bang that creates a whole new universe, which may have new stars, new planets, and new life.

In this distant universe some of your atoms may make the fingers of a holy man, who holds a pen to write the words;

Let there be light.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.