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 infrastructure emerged as environmental concerns for the rush. In Pennsylvania, controversy has surrounded the practice of releasing wastewater from "fracking" into rivers which serve as consumption reserves. Methane release contributing to global warming is a concern. The word “fracking”, slang for hydraulic fracturing, has entered the English language. The Great Shale Gas Rush refers to the growth in unconventional shale gas extraction in the early 21st-century. Pennsylvania was featured in the Academy Award-nominated, environmental documentary Gasland by Josh Fox in 2010. Most of the filming for the 2012 Gus Van Sant dramatic film, Promised Land, starring Matt Damon, took place