Query: The Ozone Layer stops UV radiation from entering our atmosphere.

Relevant passages:
Earth <=SEP=> Earth ( from Eorðe -LSB- Γαῖα , Gaia -RSB- Terra ) , otherwise known as the World or the Globe , is the third planet from the Sun and the only object in the Universe known to harbor life . It is the densest planet in the Solar System and the largest of the four terrestrial planets .   According to radiometric dating and other sources of evidence , Earth formed about 4.54 billion years ago . Earth 's gravity interacts with other objects in space , especially the Sun and the Moon , Earth 's only natural satellite . During one orbit around the Sun , Earth rotates about its axis over 365 times ; thus , an Earth year is about 365.26 days long . Earth 's axis of rotation is tilted , producing seasonal variations on the planet 's surface . The gravitational interaction between the Earth and Moon causes ocean tides , stabilizes the Earth 's orientation on its axis , and gradually slows its rotation .   Earth 's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years . About 71 % of Earth 's surface is covered with water , mostly by its oceans . The remaining 29 % is land consisting of continents and islands that together have many lakes , rivers and other sources of water that contribute to the hydrosphere . The majority of Earth 's polar regions are covered in ice , including the Antarctic ice sheet and the sea ice of the Arctic ice pack . Earth 's interior remains active with a solid iron inner core , a liquid outer core that generates the Earth 's magnetic field , and a convecting mantle that drives plate tectonics .   Within the first billion years of Earth 's history , life appeared in the oceans and began to affect the Earth 's atmosphere and surface , leading to the proliferation of aerobic and anaerobic organisms . Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago . Since then , the combination of Earth 's distance from the Sun , physical properties , and geological history have allowed life to evolve and thrive . In the history of the Earth , biodiversity has gone through long periods of expansion , occasionally punctuated by mass extinction events . Over 99 % of all species that ever lived on Earth are extinct . Estimates of the number of species on Earth today vary widely ; most species have not been described . Over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival . Humans have developed diverse societies and cultures ; politically , the world has about 200 sovereign states .

Ozone <=SEP=> Ozone -LSB- ˈoʊzoʊn -RSB- ( systematically named 1λ1 ,3 λ1-trioxidane and catena-trioxygen ) , or trioxygen , is an inorganic molecule with the chemical formula . 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 , breaking down in the lower atmosphere to or 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 of the atmosphere .   Ozone 's odour is sharp , reminiscent of chlorine , and detectable by many people at concentrations of as little as in air . Ozone 's O3 structure 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 at elevated temperatures or fast warming to the boiling point .  It is therefore used commercially only in low concentrations .   Ozone is a powerful oxidant ( far more so than dioxygen ) and has many industrial and consumer applications related to oxidation . This same high oxidising potential , however , causes ozone to damage mucous and respiratory tissues in animals , and also tissues in plants , above concentrations of about . This makes ozone a potent respiratory hazard and pollutant near ground level . However , the ozone layer ( a portion of the stratosphere with a higher concentration of ozone , from two to eight ppm ) is beneficial , preventing damaging ultraviolet light from reaching the Earth 's surface , to the benefit of both plants and animals .

Ozone layer <=SEP=> The ozone layer or ozone shield is a region of Earth 's stratosphere that absorbs most of the Sun 's ultraviolet ( UV ) radiation . It contains high concentrations of ozone ( O3 ) in relation to other parts of the atmosphere , although still small in relation 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 about 0.3 parts per million . The ozone layer is mainly found in the lower portion of the stratosphere , from approximately 20 to above Earth , although its thickness varies seasonally and geographically .   The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson . Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500 -- 6,000 K ( 5,227 to 5,727 ° C ) , except that there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum . It was deduced that the missing radiation was being absorbed by something in the atmosphere . Eventually the spectrum of the missing radiation was matched to only one known chemical , ozone . 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 .   The ozone layer absorbs 97 to 99 percent of the Sun 's medium-frequency ultraviolet light ( from about 200 nm to 315 nm wavelength ) , which otherwise would potentially damage exposed life forms near the surface .   The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer .   Venus also has a thin ozone layer at an altitude of 100 kilometers from the planet 's surface .