Physicist, Professor Happer points out carbon dioxide is an important trace gas and an integral part of the carbon cycle, a bio-geo-chemical cycle in which carbon is exchanged between the oceans, soil, rocks and the biosphere. Virtually all of life on the plant requires CO2 concentrations to be above 150 parts per million. The concentration of CO2 in the atmosphere over the past 500 million years has been as high as 4,000 ppm and as low as 180 ppm.
