Spare a moment for the mathematics: it's mind boggling. With every resting breath, we inhale (∼3 ×) 10 21 molecules of oxygen (O 2 ) and (∼5 ×) 10 18 molecules of carbon dioxide (CO 2 ), assumptions notwithstanding (Table 1). If lined up, and given Lennard-Jones kinetic diameters of 3.46 and 3.99 Å, respectively, they would each stretch out for 9,079 × 10 5 and 2,044 × 10 3 km, wrapping themselves around the Earth no less than 22,655 and 51 times, respectively (assuming Earth's average circumference of 40,075 km). Roughly 5 s later, you'll need just as many again, and that's only at rest: you'd need 20 times as many at maximal exercise!