Is my body composed of a different set of atoms from when I was born?
June 20, 2016 5:29 AM   Subscribe

I would like to know if this statement is scientifically correct, or if it's hyperbole, or if it's basically correct but requires qualification: "Most of the atoms that formed your infant body at birth are now dispersed, as your present atoms will be again, if you have the good fortune to live a few more years on this oxygen-rich planetary home."

The excerpt quoted above is from chapter 7 of Robert Hazen's The Story of Earth, on page 180 of the 2012 Viking edition. Here's some more context to the excerpt:

"Today we experience oxygen in the most intimate exchange. With every breath we take, a tiny portion of the air becomes a part of us, even as a tiny part of us becomes the air. As days pass, our bodies melt away and form again in moment-by-moment chemical reactions with oxygen. Our tissues are replaced over and over again throughout our lives, Earth's finite store of atoms recycling among air, sea, land, and all its living forms. Most of the atoms that formed your infant body at birth are now dispersed, as your present atoms will be again, if you have the good fortune to live a few more years on this oxygen-rich planetary home."
posted by paleyellowwithorange to Science & Nature (15 answers total) 21 users marked this as a favorite

Certain parts are not replaced in this way, e.g. tooth enamel, but it seems that most are.

This link has the best citations that I can find:
posted by richb at 5:36 AM on June 20, 2016 [4 favorites]

What about neurons?
posted by I-baLL at 5:56 AM on June 20, 2016

Radiolab did a great story on this.
posted by sanka at 6:13 AM on June 20, 2016

Depends on which body part, and depends on how old you are - this article explains it.
posted by julthumbscrew at 6:14 AM on June 20, 2016 [2 favorites]

Even in neurons, the atoms are replaced. It's true that adults don't grow very many new neurons, and many/most of them stay alive throughout the lifespan, but that doesn't mean the literal materials they are made of stay the same. Just like any cell, neurons respire, repair themselves, exchange molecules with their surroundings, etc.
posted by Cygnet at 6:15 AM on June 20, 2016 [3 favorites]

Although, the atoms in DNA in neurons should be composed mostly of the same atoms as when the neurons were created. (Actually true of DNA in most mature, non-dividing cells, but for most tissues the cells themselves are not that long-lived, as discussed in the previous answers and links.) It's not 100%, as DNA damage can still occur, and DNA repair mechanisms in the cell fix that damage (resulting in the replacement of some atoms within the DNA), but largely DNA is pretty constant once a cell has stopped dividing. Per Cygnet's comment, though, even most of the other components of neurons will be periodically exchanged. So it's fair to say, as in the quote, that most of the atoms in your body are exchanged, but not all.
posted by DevilsAdvocate at 6:29 AM on June 20, 2016 [2 favorites]

So... tattoos. How do they work? (serious question)
posted by quinndexter at 6:53 AM on June 20, 2016 [2 favorites]

You have your answer but Ship of Theseus is always worth a read.
posted by SaltySalticid at 6:56 AM on June 20, 2016 [2 favorites]

Re: tattoos. While the majority of your body's cells are periodically replaced, they are replaced on-site (in situ), with old/bad components being circulated into the bloodstream and cleaned up by the liver, the kidneys, etc. Imagine that your body is a house that is constantly being renovated. It's having its siding replaced, it's having the walls repainted. Getting tattooed is like slipping something INSIDE the walls. Unless there is massive physical trauma to the structure itself (e.g. road rash on a motorcycle), the ink itself is in an interstitial place, in between two areas experiencing cell turnover.
posted by julthumbscrew at 8:01 AM on June 20, 2016 [7 favorites]

So... tattoos. How do they work?

Imagine a bin of loose apples at a grocery store.

Now, gently set a bowling ball in the middle of the bin so it's not crushing any apples, but gently nestled among them.

Then, as individual apples rot, replace them with fresh apples. Not the whole bin at once, just a couple apples, here and there, as they go bad.

How long before the bowling ball is gone?
posted by AzraelBrown at 12:20 PM on June 20, 2016 [6 favorites]

Thanks! sry for threadjacking
posted by quinndexter at 2:07 PM on June 20, 2016

Related question: If someone had plastic surgery to alter their face, how come when the cells are replaced they grow to the new form and not the original DNA blueprint form?
posted by marienbad at 12:07 PM on June 26, 2016

Re: plastic surgery. Your body is not a monolithic sheet of cells, like a slab of granite. It's more like an old house, with drywall, THEN studs, THEN brick, THEN some ivy growing on the outside. The ivy is your skin. If you bash a hole in the outside wall, or put on an addition, the ivy grows AROUND the underlying shape of the hard structures underneath. This is why GOOD plastic surgery is often MODERATE plastic surgery - because there's only so much rearranging of that outermost sheet you can DO without it looking funky and engineered.
posted by julthumbscrew at 12:19 PM on June 27, 2016

I've often thought the Ship of Theseus approach to this could help reassure those who believe a real version of the Star Trek transporter would amount to murder and replacement. If that were true, then living has also, though very very slowly, murdered and replaced every one of us with an imposter. We are the system, or structure, not the exact substance, of our bodies.
posted by aught at 1:42 PM on June 27, 2016

I was thinking about this question the other day, and the answer is that surely you retain a great number of your original atoms, or at least the ones you get by adolescence.

The reason I think this is tatoos. Get a tatoo at age 15, and you'll still have it when you die. Faded, maybe, but the design will be recognisable. Your body doesn't renew the pigments, so the atoms for those must stay there. Same with, for instance, the calcium in your bones.
posted by kandinski at 12:38 AM on July 2, 2016 [1 favorite]

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