Dear Science, 

I read once that atoms get recycled so much through the planet that each of us probably includes a little bit of Shakespeare. Can this be true? (And if it is, why is my poetry still so bad?) Where do our atoms come from, anyway?

Here’s what science has to say:

I can’t say for sure whether a piece of you came from William Shakespeare, but I do know this: All of us come from stars.

Suzanne Bell, an analytical chemist at West Virginia University, estimates that a 150-pound human body contains about 6.5 octillion (that’s 6,500,000,000,000,000,000,000,000,000) atoms. The vast majority of them are hydrogen (humans are almost entirely water, which comprises two hydrogen atoms and an oxygen).

All that hydrogen was made in the early days of the universe, about 380,000 years after the Big Bang. At that point, conditions had cooled enough for electrons to get trapped in orbit around nuclei — forming the very first atoms. A single electron circling a single proton created hydrogen; two electrons around a nucleus of two protons and two neutrons made helium.

From these materials formed the first stars, which condensed out of the clouds of helium and hydrogen gas that filled the universe more than a million years after its creation. Stars are fusion factories, powered by smashing atoms together in their hot, dense interiors. Younger, smaller stars, like our sun, burn hydrogen into helium. Older and more massive ones are hot enough to turn three helium atoms into carbon, or four heliums into oxygen. This is how the next 2½ rows of the periodic table — every element up to iron — got created.

This is also where most of the remainder of your atoms come from. According to Bell’s calculations, about a quarter of your atoms are oxygen atoms, a tenth are carbon and another 1 percent are nitrogen — all elements produced in the interiors of stars.

As stars progress through their life cycles, getting denser and denser, hotter and hotter, their cores become full of heavier and heavier elements. At 1,080 million degrees Fahrenheit, carbon fuses into neon. Double the temperatures to turn oxygen into silicon. Finally, at 7,200 million Fahrenheit, silicon fuses into iron.

At this point, the star factory runs out of fuel. Burdened by its heavy iron heart, the star will collapse, then explode, dispersing the elements in its interior and creating new ones.

Supernovae are the sources of all the elements after iron. These elements are present in humans only in trace amounts, but they’re easily spotted if you know where to look. If you have gold fillings in your teeth, those atoms came from a star explosion. So did the zinc that your body requires to make enzymes, the iodine in thyroid hormones and the manganese needed for your bones.

Every tiny bit of your body was either once inside a star or produced during its death throes. “We are stardust,” to quote Joni Mitchell (and Carl Sagan).

But if you’re still wondering about that bit of the bard, let’s look at what happens next.

An atom — let’s say, carbon — got produced in a star factory. After several billion years in operation, the star blew up, and the atom was released into the dark void of space. Eventually, it joined a cloud of gas and dust in a remote corner of the Milky Way galaxy. That’s the beginning of our solar system. Roughly 4.5 billion years ago, something jostled the gas cloud and caused it to collapse and start to spin. The center formed our sun, while the stuff on the outside began accreting into planets, asteroids and comets.

Our little carbon atom wound up on a comet — the balls of ice, rock and organic compounds that circle our solar system — and at some point smashed down to Earth. Maybe it spent a few hundred million years locked up inside a rock in the Earth’s crust, until a volcano erupted, breaking through the crust and spewing the atom into the atmosphere, where it joined with two oxygen molecules to make carbon dioxide. Then a plant plucked the molecule from the air, stripped the carbon of its companions, and forced it into a new molecule — glucose. Maybe hungry Apatosaurus strolled by next, chomped down the plant, processed the sugar and then breathed the carbon back into the air as carbon dioxide.

Time passed and the carbon atom cycled through this process a few billion more times until 1616, when it wound up in a carrot grown on farm in Stratford-upon-Avon. The carrot got eaten by an ailing William Shakespeare. When Shakespeare died shortly afterward, the carbon was buried beneath Holy Trinity Church along with the man’s body. It continued to move through the carbon cycle — air, plant, animal, earth, air again — and yes, maybe, it then drifted across the Atlantic, got bound up in a plant and was eventually eaten by you.

“It’s plausible,” Bell said, when asked to consider whether a carbon atom in a person in Washington in 2016 could have been part of Shakespeare 400 years ago.

Then again, it’s also plausible that your carbon atoms were once part of volcanoes, giant redwoods, Apatosauruses, diamonds, plastic bottles, snakes, snails, lichens, nematodes, photosynthetic algae, the very first cells. It’s certain that your carbon saw the interior of a star, survived a supernova, sailed through the solar system and splashed down on Earth long before arriving at you. Breathe in and marvel at that fact.

Now breathe out. Riding an invisible cloud of carbon dioxide, a carbon atom just left your body, headed for its next great adventure.

It may not be a Shakespearean sonnet, but I think that’s pretty poetic.