"Since about 1 per cent of your breath is argon we can determine approximately the number of atoms in your next argonic intake. The calculations are really rather simple and straightforward, but to some readers this dizzy arithmetic is repulsive and I shall simply state the results. In your next determined effort to get oxygen to your lungs and tissues you are taking in, besides the nitrogen and oxygen, 30,000,000,000,000,000,000 atoms of argon; in briefer statement 3 X 10^19. (Count the zeros!) A few seconds later you exhale those argon atoms along with quintillions of molecules of carbon dioxide.
"Now let us follow the career of one argon-rich breath in your next exhalation, let us suppose. We shall call it Breath X. It quickly spreads. Its argon, exhaled this morning, by nightfall is all over the neighborhood. In a week it is distributed all over the country; in a month, it is in all places where winds blow and gases diffuse. By the end of the year, the 3 X 10^19 argon atoms of Breath X will be smoothly distributed throughout all the free air of the earth. You will then be breathing some of those same atoms again. A day's breathing a year from now, wherever you are on the earth surface, will include at least 15 of the argon atoms of today's Breath X.
"This rebreathing of the argon atoms of past breaths, your own and others', has some picturesque implications. The argon atoms associate us, by an airy bond, with the past and the future. For instance, if you are more than twenty years old you have inhaled more than 100 million breaths, each with its appalling number of argon atoms. You contribute so many argon atoms to the atmospheric bank on which we all draw, that the first little gasp of every baby born on earth a year ago contained argon atoms that you have since breathed. And it is a grim fact that you have also contributed a bit to the last gasp of the perishing.
"Every saint and every sinner of earlier days, and every common man and common beast, have put argon atoms into the general atmospheric treasury. Your next breath will contain more than 400,000 of the argon atoms that Gandhi breathed in his long life. Argon atoms are here from the conversations at the Last Supper, from the arguments of diplomats at Yalta, and from the recitations of the classic poets. We have argon from the sighs and pledges of ancient lovers, from the battle cries at Waterloo, even from last year's argonic output by the writer of these lines, who personally has had already more than 300 million breathing experiences. Our next breaths, yours and mine, will sample the snorts, sighs, bellows, shrieks, cheers, and spoken prayers of the prehistoric and historic past.
Harlow Shapley, Beyond the Observatory
Mass of atmosphere = 6E15 tons (radius of earth= 4000 miles; weight = 14.7 lb/in2
Volume adult human lungs = 5 L
