The Earth's layers of atmosphere differ in chemical composition and temperature. They combine to create a protective sheild that maintains our delicate energy balance essential for life on Earth. Most weather occures in the nearest layer, the troposphere (0-7 miles). The stratosphere is the level where jet airliners fly and the ozone layer resides (7-30 miles). Beyond that is the coldest part of the atmosphere, the mesosphere where only large helium balloons fly (30-50 miles). Finally, the thermosphere gradually fades into space (50-180 miles).
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 188.8.131.52.0