" In breathing, as in everything in life, the numbers are staggering – indeed fantastical. Every time you breathe, you exhale some 25 sextillion (that’s 2.5 × 1022) molecules of oxygen – so many that with a day’s breathing you will in all likelihood inhale at least one molecule from the breaths of every person who has ever lived.1 And every person who lives from now until the sun burns out will from time to time breathe in a bit of you. At the atomic level, we are in a sense eternal. "

― Bill Bryson , The Body: A Guide for Occupants