A zettagram (Zg) is an SI unit of mass representing 10^21 grams, or 10^18 kilograms. It is a planetary-scale unit used in geophysics and astronomy. For context, the entire mass of the Earth's atmosphere is approximately five zettagrams, and the mass of the Earth's oceans is around 1.4 million zettagrams.
Heard on the job
The total atmospheric mass is estimated at just over five zettagrams.