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Every breath we take is comprised of recycled atoms, first released by stars and then used by countless ...
2021-01-19 09:00:00

From the Stars to Our Lungs
The Great Atomic Cycle

From the Stars to Our Lungs

With every breath, we absorb atoms that were previously used by countless other creatures who share the Earth with us. Some of them become us for a moment, after which they return to the great cycle of nature.

Read in 11 minutes

The pandemic has locked all of us up in our own private, masked atmospheres – we would give a lot for a chance to breathe air that is exclusively ours, completely devoid of any virus transmission risk. Air that was never breathed by anyone, never touched, never pushed through the tubing of nostrils, pipelines of tracheae, never squeezed by the decompressing, wrinkly bags of lungs. And what if I tell you that this wish is (almost) impossible to fulfil? It just so happens that when living on Earth – even if we only go for a trek in the desolate mountains – we breathe each other.

There is plenty of matter in the world. Take a little water into your hand: inside, there will be 250,000 billion billion atoms floating in it, some of them on their own, others connected to make strange shapes and zigzags not unlike those particle models you used to make out of matches during chemistry lessons at school. And that’s just a tiny portion of matter you hardly got to touch, a portion so small it might as well not be there at all. If we counted all the atoms of matter that exist on Earth and inside it, every single one – from the particles of iron in the planet’s core to the atoms of oxygen and nitrogen that mix with the emptiness of space, up in the highest layers of the atmosphere – it would make for a wild, beautiful number with no name. One and 50 zeroes. We could try and clumsily name it one billion billion billion billion of billions – but what for? Everything we will ever eat and expel, everything we nip from a nearby tree or release from our lungs, all of it will consist of the same atoms, infinitely circulating along the eternal motorways and cycles, forever used anew. The cosmic recycling and constant devouring of atoms, long dead and released from all those who lived before us. But some of those... well, some are special. They are more ‘dead’ than others.

Cream roll

An atom is a hard cookie. Not easy to split, it gave physicists something to chew on for quite a while. And when they finally figured out how to do it, they decided it would have been better if it had never happened. Splitting the atom is tampering with the most basic forces that keep the entire universe together, and it leads to – among other effects – the creation of immense amounts of energy. When wrongly directed or uncontrollably released, the energy created from splitting an atom turned out to be one of the most malicious forces humanity has ever encountered.

When it comes to most of the atoms we encounter in our daily life, however, we needn’t worry about them splitting. This is a property of large atoms, such as uranium, plutonium or radon. The smaller, everyday atoms we chew on with our food, inhale with the air and drink with a cup of green tea are surprisingly stable and remain in the same shape virtually forever.

Just think about it: you eat some cake. The sweet cream is packed with carbohydrates, so we know one thing for sure – that you’re chewing on a concentrated mixture of carbon, hydrogen and oxygen (hydrogen and oxygen being the ‘water’ in carbo-hydrates). The perfectly-shaped hexagonal bricks they’re made of (known as monosaccharides) are connected in long chains – that’s where the water is caught, giving the cream its thickness, moisture and wonderful smoothness. Elsewhere, monosaccharides connect in pairs, creating disaccharides such as saccharose. They are the perfect shape for the receptors of sweetness on our tongue, fitting them as a key fits a lock. Carbon, it’s all about carbon; it’s the building material for our bodies and the component of our food. You sink your teeth into the sweet filling and your salivary glands explode, flooding the bite with a mixture of enzymes – all of it to release carbon from the food, to begin digesting carbohydrates right now, before they even begin their travel through your oesophagus and deeper inside the body. Life is ruled by carbon, and you’re now feeding your body with its most precious, most energy-rich source. But where does the carbon come from? After all, the confectioner didn’t mix it in a bowl, nobody produced it in some mysterious factory. It was already there, in white sugar and fluffy flour, in milk and cream. That’s too many paths to follow; let’s focus on just one.

Sugar. The carbon in sugar is a warehouse of easily accessible power, thanks to its energy-rich chemical bonds with hydrogen. White sugar (or saccharose, as it’s known in chemistry,) is pretty much just the essence of energy reserves stored in the root of a seemingly inconspicuous plant known as sugar beet.

Seeing just the top part of the beet – the part sticking out from the ground – we would walk right past it without even the briefest of glances. Nothing but a boring tail formed of the plainest leaves imaginable. Luckily, though, someone was smart enough to try and taste the part hiding in the soil, unexpectedly discovering its unmatched sweetness. Having done that, however, they brought a new worry upon the world, equipping us with a source of calories that turned out to be too rich and easy to process.

But where does the beet get all that sugar from? And how did carbon get into the sugar that made your cream roll so blissfully sweet? Well, the beet made the sugar all by itself! Humans, along with every other single animal on the planet, are forced to obtain our food by hunting other beings, eating plants, or finding any other way of nicking sugar from other organisms (some species wait for their prey to die first, but whatever floats your boat). In order to provide our body with the sugar it needs, we have to eat it. Plants, however, obtain it in a much more sophisticated way. They just breathe it in. Every day, their green leaves absorb plenty of air through hundreds and thousands of microscopic crevices that cover the bottom side of every leaf. Along with that air, they get carbon dioxide. The very same we consider to be a waste product of our existence. Indeed, carbon dioxide on its own is rather useless, which is why plants enrich it with energy. With the use of chloroplasts, they absorb energy that falls on the Earth in photon rains sent here by the sun. There, in chloroplasts, carbon dioxide and hydrogen (coming from water) merge into molecules of sugar, packed with solar energy. Then, those molecules travel through microscopic waterways to the farthest parts of the plant. Some of those molecules are used up by the plant just to stay alive, while others (the surplus) are sent to the pantry – the organs whose job it is to store sugar for some other time.

That’s when we get to the core of our atomic investigation. Those atoms of carbon – joined together so deliciously and cleverly to give us the impression of sweetness – are exactly the same atoms that were absorbed by some sugar beet with its stomata a long time ago. Seasoned with hydrogen, packed with sunlight energy, those atoms are still pretty much the same. They haven’t changed much on their way into your cream roll (a chemist would say that their level of oxygenation has changed, but that’s only a fine chemical detail, 100% reversible). And while the following information might sound a bit less appetizing, let’s keep in mind that the plant does not care where its carbon dioxide came from. You could be enjoying a cream filling made of carbon released from some hot springs in Iceland and Yellowstone, brought to Europe by stratospheric winds. Or perhaps it was discharged by a parasol mushroom’s mycelium in a nearby meadow when it was munching on some of the delicious leftover cowpat and decaying plants that make for the parasol mushroom’s favourite spread. It could also be the carbon floating above that rotting piece of bread, quietly devoured by green mould in a forgotten corner of your kitchen cupboard. And maybe it was the carbon dioxide expelled by a diva who sang Un bel di, vedremo on stage, giving goosebumps to the audience of Madame Butterfly.

Dinosaur air

Whenever you breathe or eat your favourite snack – or do anything that involves absorbing atoms – you participate in a great act of planetary recycling of the tiniest bricks of matter. Complex equations and mathematical somersaults aside (those would need to include the number of atoms on Earth, the fraction of atoms actually available to humans, the number of atoms in our body and the pace of their ‘exchange’, along with the cells dying and being expelled from the body) it could be easily proven that the chance of inhaling atoms that someone else has exhaled is – watch out – 100%! This means not only that we most likely breathe the same atoms all people living on Earth ever have and ever will breathe. It can be said with almost absolute certainty that your lungs have pumped the same atoms that were once inside Albert Einstein. And Louis Armstrong. And Frida Kahlo. And the saleswoman in your local grocery shop. And every single person who has had the pleasure to walk on this planet.

Photo by Wil Stewart / Unsplash
Photo by Wil Stewart / Unsplash

Of course, there is a way to – for at least a moment – breathe air that is considerably older than us. Even particles that were almost certainly never inside the lungs of any other human being. In order to experience this, you would have to go on a trip. Carbon dioxide in the atmosphere usually just travels between various molecules containing carbon, but sometimes it ends up in a ‘carbon prison’. This happens when it’s absorbed by an organism that locks it up in transparent crystals of calcium carbonate. These crystals are very hard and almost insoluble in water. Such a trick can be performed by forams, tiny protozoa that live in microscopic carbonate shells. Billions of forams used to live in the oceans, and billions of them still do. After forams die, carbon locked in their shells simply falls down to the sea floor and remains there until it eventually transforms into hard calcium rock. Those atoms of carbon are sentenced to eternal stillness, unless we help them escape.

One time, when teaching a group of young people about atoms and their constant travel, I took my students to Mnikowska Valley. Its steep white walls are layers of calcium, remnants of warm seas that existed here in the Mesozoic era. Hundreds and thousands of tonnes of ancient carbon dioxide, locked inside a rock. I took a calcium lump in my hand. I crumbled it between my fingers and threw it inside a small plastic bag. Then, I poured in a few drops of vinegar. Suddenly, the rock came to life. The acid from the vinegar bit into the calcium and released prehistoric carbon, fizzing in a feast of foamy carbon dioxide, escaping its prison. We could breathe in some of that vinegary gas. Just not too much – let’s keep in mind that, after all, carbon dioxide is a by-product of our breathing process, unlike life-giving oxygen. With this simple trick, we returned a small portion of CO2 into its modern currents that circulate in the atmosphere. It was a portion never inhaled nor exhaled by a human being. Maybe a hundred million years ago, some dinosaur breathed those particles? Or maybe it was released by some Jurassic carrion, or by a volcano spitting fire and lava everywhere?

Cosmic puffballs

Just the very thought that nothing on this planet is truly ours – that with every minute, we absorb and expel masses of foreign atoms, already used by someone else and then returned to circulation and reused by organisms we eat – that concept is deeply inspiring. Biologically, we are part of the life-and-death cycle, but it is the level below it that reveals the true unity of everything that roams this planet. Nothing is special, and nothing really stands out with this sloshing, bubbling atomic soup. Some atoms just become us for a moment, lending us the opportunity to keep living the conscious life, and after that moment, they return to circulation, end up in someone else, or are forever locked somewhere in the dark depths of the ocean.

But that’s not quite the end – there is one more level. We could ask another question: how did those atoms appear on Earth in the first place? Carbon, present in our cream roll as well as in every millimetre of every hair on our head, all of it was here since the beginning of our planet. But it did not appear from nothing. Atoms in the cosmos, at its very beginning, were relatively unexciting. In its youth, the universe was made almost exclusively of hydrogen and helium, the two lightest elements, gasses that, in the pre-cosmos, created great tumbling clouds and nebulas. Everything changed 300 to 400 million years later, when those clouds thickened enough for the first stars to light up within them.

Stars are alchemical wonderlands, forges of chemical elements that emerge from a series of thermonuclear reactions that connect simpler atomic nuclei together in astronomically high temperatures. Inside stars, new elements are born; in many cases (if the star isn’t too large), the entire process ends with carbon. Such a star dies peacefully, gradually losing its external layers (already enriched with heavy elements) and becoming a white dwarf – a densely packed, white-hot ball of carbon. But sometimes, if the star is large enough, the carbon inside it will spark another thermonuclear reaction, hotter and more violent, creating more heavy elements: oxygen, sulphur, silicon, nickel, iron. And that’s as heavy as it gets, for iron is the absolute limit of any ‘regular’ star’s capabilities. The iron core of a great star, surrounded with sheets of lighter elements – like a multi-layered cosmic onion – collapses. The star is torn apart by a bow shock that crushes the core into a neutron star, sometimes even creating a black hole. Meanwhile, the energy released by the explosion (known as a supernova) is so great that in a split second, it produces a whole spectrum of other elements heavier than iron. The star’s life ends in a giant cosmic firework, its body scattered everywhere around, raining elements from all corners of the periodic table.

I like to think of it as a great farm of cosmic puffballs. There they are, growing, swelling up for billions of years, glowing in the cosmic darkness, until finally they die in giant soundless explosions. All that’s left of them are clouds of cosmic dust, chemical sporules swirling in space, mixing with emptiness and travelling along the cosmic pathways. Here and there, by some twist of fate, they slowly become denser, lighting up new stars inside them. And around those stars, there can be planets moulded from the same stardust, sometimes – like in the Earth’s case – sparing enough of it to allow life to develop. In a galaxy such as our Milky Way, two to four supernovas explode every century. When we think of the universe, with its billions of galaxies, we can suddenly visualize a cosmos constantly sparkling with fireworks. And there, we and others just like us are born from the remains of those dead stars to exchange prehistoric atoms through our inhaling and exhaling.


Translated from the Polish by Aga Zano

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Szymon Drobniak

is an evolutionary biologist, researcher on colour, ornithologist, illustrator and author. A passionate fan of diagrams, cross-sections and pea soup. In his spare time, he collects roots (not the mathematical kind).