The Earth is surrounded by a gaseous envelope which we call the atmosphere. This atmosphere extends over our heads for about 1,000 miles- becoming thinner and thinner and finally merging into interplanetary space.
Shaw, R. H. and Elford, C. R.
"The Air We Live In,"
Iowa Farm Science: Vol. 12
, Article 3.
Available at: https://lib.dr.iastate.edu/farmscience/vol12/iss10/3