Atmosphere of Earth the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around . Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around
Shale gas in the United States thickness of the Barnett varies from 100 to , but most economic wells are located where the shale is between 300 and thick. The success of the Barnett has spurred exploration of other deep shales. In 2007, the Barnett shale (Newark East) gas field produced of gas, making it the second-largest source of natural gas in the United States. The Barnett shale currently produces more than 6% of US natural gas production. In April 2015, Baker Hughes reports that there are 0 rig currently in activity at the Barnett gas field. (That doesn't mean 0 production as there are still