Some of the gases in Earth's atmosphere, such as CO2, are called greenhouse gases. Greenhouse gases interact with sunlight in a way that traps heat in the atmosphere. By trapping heat, greenhouse gases help insulate Earth. The table below lists some important greenhouse gases and their atmospheric concentrations in units of parts per million (ppm), parts per billion (ppb), or parts per trillion (ppt).

Greenhouse gas Concentration in 2015

Carbon dioxide (CO2) 400 ppm

Sulfur hexafluoride (SF6) 9 ppt

Methane (CH4) 1,750 ppb

Nitrous oxide (N2O) 325 ppb

Use the data in the table to put the following greenhouse gases in order of atmospheric concentration.

Hint: A concentration of 1 ppm is 1,000 times more than 1 ppb, and 1 ppb is 1,000 times more than 1 ppt.