CG: n

CT: The ozone layer is a belt of naturally occurring ozone gas that sits 9.3 to 18.6 miles (15 to 30 kilometers) above Earth and serves as a shield from the harmful ultraviolet B radiation emitted by the sun. Ozone is a highly reactive molecule that contains three oxygen atoms. It is constantly being formed and broken down in the high atmosphere, 6.2 to 31 miles (10 to 50 kilometers) above Earth, in the region called the stratosphere. Today, there is widespread concern that the ozone layer is deteriorating due to the release of pollution containing the chemicals chlorine and bromine. Such deterioration allows large amounts of ultraviolet B rays to reach Earth, which can cause skin cancer and cataracts in humans and harm animals as well.

S: National Geographic – http://environment.nationalgeographic.com/environment/global-warming/ozone-depletion-overview/ (last access: 16 December 2014).

N: 1. ozone (n): 1840, from German Ozon, coined in 1840 by German chemist Christian Friedrich Schönbein (1799-1868) from Greek ozon, neuter present participle of ozein “to smell”. So called for its pungent odor.
layer (n): late 14c., “one who or that lays” (especially stones, “a mason”), agent noun from lay (v.). Passive sense of “that which is laid over a surface” first recorded 1610s, but because earliest English use was in cookery, this is perhaps from French liue “binding,” used of a thickened sauce. Layer cake attested from 1881.
2. The ozone layer is one layer of the stratosphere, the second layer of the Earth’s atmosphere. The stratosphere is the mass of protective gases clinging to our planet.
3. The ozone layer absorbs a portion of the radiation from the sun, preventing it from reaching the planet’s surface.
4. The initial concern about the ozone layer in the 1970s led to a ban on the use of CFCs as aerosol propellants in several countries, including the U.S. However, production of CFCs and other ozone-depleting substances grew rapidly afterward as new uses were discovered.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=layer&searchmode=none (last access: 16 December 2014). 2. National Geographic – http://education.nationalgeographic.com/education/encyclopedia/ozone-layer/?ar_a=1 (last access: 16 December 2014). 3 & 4. EPA – http://www.epa.gov/ozone/science/sc_fact.html (last access: 16 December 2014).

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CR: air pollution, biosphere, chlorofluorocarbon, environment, ionosphere, mesopause, mesosphere, stratosphere, stratospheric ozone, tropospheric ozone.