I know we are all made of “star stuff”. That’s not what I’m wondering about.
Take your average, run-of-the-mill, standard-issue twenty-year-old today. The molecules that make up his or her brain … the brain that is now forming its own thought and opinions … where were those molecules twenty-five years ago?
The molecules the skin and bone structure of his or her face that today creates beauty (or lack thereof)… where were they twenty-five years ago?
In the cells of other living organisms, including parents, plants and other foods, such as meats.
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Or in the earth’s crust. Or the atmosphere. Or the ocean. Plants extract nutrients from the soil/water and carbon dioxide from the air, then animals eat those plants (or eat animals that have eaten those plants). Then we eat those animals (or we eat those plants).
If you eat anything with added salt, that salt may have come from a mine where it sat undisturbed for millions of years.
For agriculture, the chemicals and fertilizers applied to the crops and fields are manufactured elsewhere and trucked in. Likewise with the feed for many farmed animals.
25 years ago, the atoms in your run-of-the-mill now-20YO could have been anywhere on (or in) the planet, especially with international commerce bringing you food from all over the world these days.
Could have been in poop, too. We are all made of some am’t of poop.
A lot of the molecules, such as proteins and nucleic acids, were built in the 20-year-old’s body from atoms (and smaller molecules) that were all over the place.
Even more awe inspiring, some of that poop was once Leonardo da Vinci’s poop.
Perhaps some of us are, but I for one am definitely not. Only quality “Grade-A” molecules went into making me.
So what you’re saying is, the poop you’re made of don’t stink?
[bizarre hijack/] This seems like as good a place as any to ask one of my more exotic questions. Forgive any gross ignorance of basic biochemistry. We’re carbon-based beings, right? So the GATC of our DNA must contain atoms of carbon in its makeup.
Could a human being have a different isotope of carbon, say Buckyballs, substituted for all the regular carbon atoms in their DNA or tissue or whatever, and live? [/bizarre hijack]
Buckyballs are an arrangement of carbon atoms, right?. Once they’re broken apart and used for DNA or tissue whatever former structure they were in is no longer relevant. You couldn’t take a C[sub]60[/sub] and use it in the human body as a building block. It would have to be broken down into individual carbon atoms and reassembled into the required configurations.
Buckyballs aren’t an isotope, they are an arrangement. Is that correct?
Buckyballs are not an isotope of carbon. They are a carbon molecule. Buckyballs are made up of 60 carbon atoms.
As others have pointed out that buckyballs are an allotrope of carbon, not an isotope.
All living things do contain a certain amount of carbon-13 and carbon-14 as well as the much more common carbon-12. Indeed carbon-dating relies on the presence of carbon-14.
As a non-expert guess, I’m guessing you could replace a lot the carbon-12 in someone’s body with carbon-13.
And you could make organic molecules out of some other isotope, and aside from hydrogen isotopes, it won’t make any significant difference to the organism. Doing this is a very useful way of learning how chemical reactions proceed in an organism, since you can put a few “tracer isotopes” in the molecules that go in, and see where they end up in the molecules that come out. In fact, a lot of catalysts, which speed up a chemical reaction but are supposedly unchanged by it, actually turn out to be taken apart during the reaction but then put back together with different atoms.
Nitpick: It might not make any chemical difference, but if you replace everything with radioactive isotopes it probably will make a significant difference to the organism. 
And to add to Chronos’s post; as I understand it, the only chemical differences between isotopes are due to the differing masses of the atomic nuclei since different isotopes have differing numbers of neutrons. For almost every element, that appears to make no significant difference because a neutron on way or the other doesn’t change the mass much. Hydrogen being the exception because it has only a single proton, so adding on a neutron or two does make it significantly more massive and change its chemical behavior. Various odd things happen when you give organisms only heavy water (which has mostly deuterium instead of mostly normal hydrogen) to live on.
Even with hydrogen, the chemical differences between normal hydrogen and deuterium are very, very small. The only reason they’re relevant at all is because biological systems are very, very delicate.
Star dust. For your penance, say 3 Woodstocks and 5 Hail Hendrickses.
i was built up on royal molecules. bow down, you commoners!
Wait a second. Was our OP trying to update a koan? What did your face look like before your parents were born?
Okay, my mistake. I was unclear on the difference/relationship between relative atomic mass, atomic mass, atomic number, and isotopes.
I looked up the effects of heavy water on human physiology. Bummer. I was hoping for some kind of spiderman thing. 
Well, if we are talking about a 20 year old it could just as well be Leonardo Dicaprio’s poop.