Traveling across the Earth
Once on Earth, your atoms 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.
The average person is made of seven octillion atoms, which is a number so great that it is almost impossible to conceptualise. Seven octillion is a seven followed by twenty-five zero’s. If you had seven octillion standard sized bricks, they’d fill the volume of the planet Jupiter… four times over.
They no doubt that this huge number of atoms combined into different molecules and broke down again billions of times. But the atoms themselves have 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 — up to a billion for each of us, it has been suggested — 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 — though short-lived ones. When we die, our atoms will disassemble and move off to find new uses else-where — 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 at the birth of life on Earth.
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 the muscle tissue of both a Tyrannosaurus and its prey.
In the chaos of Earth’s ever-changing chemistry, it seems like our seven octillion atoms have truly been everywhere.
Eventually, through your digestion of food and metabolism, some of your atoms came together to create your hands, heart, and the eyeballs you’re using to read these words.
One thing we know for sure though is that your carbon atoms were very recently part of a plant, and considering our modern diet, it was probably corn or wheat. The plant pulled in carbon dioxide molecules floating in the air and 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.
The last glass of water you drank 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 through 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 — 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 borrowing them.
“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 Earth: The long future of your atoms
After another five billion years of cycling around the Earth, all atoms on our planet will be scorched by the Sun as it expands into the final stage of its life, a red giant.
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The Sun’s outer layers will expand 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, completely 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 the 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.
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 the remaining hydrogen and helium, and the galaxies will go dark.
The end of the road?
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, where the time scales are so long that time begins to lose its significance, even the black holes disappear, evaporating into nothing but radiation.
This is the end of the line of what scientists know will happen for sure.
Or will it all begin again?
But there is much 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 the quarks that they consist of.
These particles will fill the universe in a ‘thermal equilibrium’, where every place in the universe is barely above a temperature of absolute zero, and no further exchange of energy becomes possible.
This means no stars, life, or intelligence will be possible. It may 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 first slowly, and then rapidly 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.
There may be a new Big Bang that creates a whole new, different universe, which may one day have new stars, new planets, and new life.
In this distant universe, the energy that was once you may one day cycle through a planet and its creatures once again.
It may form the light of a distant star that impacts the retina of a scientist or storyteller who wonders about the universe, and where her own atoms came from.