From Nova Science Now, by Peter Tyson:
You and everything around you, every single natural and man-made thing you can see, every rock, tree, butterfly, and building, comprises atoms that originally arose during the Big Bang or, for all but the lightest two or three elements, from millions of burning and exploding stars far back in the history of the universe. You live because stars died; it’s that simple.
How is this so? How can you possibly be a walking galaxy of fossil stardust? Well, the story is not a new one, but it bears retelling, if only because its working out was one of the finest achievements of 20th-century astrophysics—and because it’s so astonishing.
The start of it all
The story begins at the beginning, as in the Big Bang. That is when, astrophysicists say, all the hydrogen in the universe came into being. Initially it was just protons, and then, as the young universe expanded and cooled, these became bound to electrons, forming hydrogen atoms. The very hydrogen atoms in the H2O that makes up over half your body were born then. They didn’t come from your parents; they came from the early universe. Did you have any idea you have atoms in your body that are over 13 billion years old?
If you could separate one hydrogen atom from one molecule of water in your body, shrink down to its atomically tiny size like the scientists in Fantastic Voyage, then reverse time and follow it back to through its unimaginable lifetime, you would find yourself in the immediate aftermath of the Big Bang. That very hydrogen atom, an atom now inside you as you read this, has remained unchanged since the beginning of time…