Radon concentrations found in natural environments are much too low to be detected by chemical means. A 1,000 Bq/m3 (relatively high) concentration corresponds to 0.17 picogram per cubic meter (pg/m3). The average concentration of radon in the atmosphere is about 6 molar percent, or about 150 atoms in each milliliter of air. The radon activity of the entire Earth's atmosphere originates from only a few tens of grams of radon, consistently replaced by decay of larger amounts of radium, thorium, and uranium.