Ozone layer

The ozone layer or ozone shield refers to a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet (UV) radiation. It contains high concentrations of ozone (O₃) relative to other parts of the atmosphere, although still very small relative to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is only about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, though the thickness varies seasonally and geographically.

The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The "Dobson unit", a convenient measure of the amount of ozone overhead, is named in his honor.

Ozone

Ozone /ˈoʊzoʊn/ (systematically named 1λ¹,3λ¹-trioxidane and catena-trioxygen), or trioxygen, is an inorganic molecule with the chemical formula O
3. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O
2, breaking down in the lower atmosphere to normal dioxygen. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth's atmosphere (stratosphere). In total, ozone makes up only 6993600000000000000♠0.6 ppm of the atmosphere.

Ozone's odour is sharp, reminiscent of chlorine, and detectable by many people at concentrations of as little as 6992100000000000000♠10 ppb in air. Ozone's O₃ formula was determined in 1865. The molecule was later proven to have a bent structure and to be diamagnetic. In standard conditions, ozone is a pale blue gas that condenses at progressively cryogenic temperatures to a dark blue liquid and finally a violet-black solid. Ozone's instability with regard to more common dioxygen is such that both concentrated gas and liquid ozone may decompose explosively. It is therefore used commercially only in low concentrations.

Arctic

The Arctic (/ˈɑːrktɪk/ or /ˈɑːrtɪk/) is a polar region located at the northernmost part of the Earth. The Arctic consists of the Arctic Ocean and parts of Alaska (United States), Canada, Finland, Greenland (Denmark), Iceland, Norway, Russia, and Sweden. The Arctic region consists of a vast ocean with a seasonally varying ice cover, surrounded by treeless permafrost. The area can be defined as north of the Arctic Circle (66° 33'N), the approximate limit of the midnight sun and the polar night. Alternatively, it can be defined as the region where the average temperature for the warmest month (July) is below 10 °C (50 °F); the northernmost tree line roughly follows the isotherm at the boundary of this region.

Socially and politically, the Arctic region includes the northern territories of the eight Arctic states, although by natural science definitions, much of this territory is considered subarctic. The Arctic region is a unique area among Earth's ecosystems. For example, the cultures in the region and the Arctic indigenous peoples have adapted to its cold and extreme conditions. In recent years, the extent of the sea ice has declined. Life in the Arctic includes organisms living in the ice, zooplankton and phytoplankton, fish and marine mammals, birds, land animals, plants and human societies.

Keke Palmer discography

The discography of Keke Palmer, an American R&B singer-songwriter, consists of one studio album, one extended play, three mixtapes and seven singles. In 2005, Palmer signed a record deal with Atlantic Records. Palmer released her debut album So Uncool on September 18, 2007. The album failed to chart on the US Billboard 200, but did chart at number 85 on the R&B chart. The album was preceded by the lead single "Keep It Movin'". In 2010, Palmer was signed by the Chairman of Interscope Records, Jimmy Iovine, and began working on an album.

In January 2011, Palmer released her first mixtape Awaken. The mixtape was officially released on January 10, 2011, for downloads on mixtape-downloading websites. The first and only single released from the mixtape was "The One You Call". A music video was also released for the song. In July 2012, Palmer released the single "You Got Me" featuring Kevin McCall. The video for the single was released on July 11, 2012. Palmer released a self-titled mixtape Keke Palmer on October 1, 2012. It includes her new singles "You Got Me" & "Dance Alone" which have already been released. On May 16, 2013, Keke Palmer released a video showing her recording and performing a cover of Alicia Keys song "If I Ain't Got You".

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