Carbon dioxide in Earth's atmosphere

Carbon dioxide is an important trace gas in Earth's atmosphere currently constituting about 0.04% (400 parts per million) of the atmosphere. Despite its relatively small concentration, is a potent greenhouse gas and plays a vital role in regulating Earth's surface temperature through radiative forcing and the greenhouse effect. Reconstructions show that concentrations of in the atmosphere have varied, ranging from as high as 7,000 parts per million during the Cambrian period  about 500 million years ago to as low as 180 parts per million during the Quaternary glaciation of the last two million years.