Once scientists knew the diameter of a typical atom, they could estimate the number of atmos in the typical human body. That number? 10,000,000,000,000,000,000,000,000,000. It means that the atoms in a human body are far, far more numerous than the sand grains on all the beaches of the Earth; than [all] the leaves and needles on all the trees of the Earth's forests. Waves in an Impossible Sea - Matt Strassler