Query: If we halve the carbon dioxide content of the atmosphere, all life dies.

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Atmosphere of Mars <=SEP=> The atmosphere of Mars is the layer of gases surrounding Mars . It is composed mostly of carbon dioxide . The atmospheric pressure on the Martian surface averages 600 Pa , about 0.6 % of Earth 's mean sea level pressure of 101.3 kPa . It ranges from a low of 30 Pa on Olympus Mons 's peak to over 1155 Pa in the depths of Hellas Planitia . This pressure is well below the Armstrong limit for the unprotected human body . Mars 's atmospheric mass of 25 teratonnes compares to Earth 's 5148 teratonnes with a scale height of about 11 km versus Earth 's 7 km .   The Martian atmosphere consists of approximately 96 % carbon dioxide , 1.9 % argon , 1.9 % nitrogen , and traces of free oxygen , carbon monoxide , water and methane , among other gases , for a mean molar mass of 43.34 g/mol . There has been renewed interest in its composition since the detection of traces of methane in 2003 that may indicate life but may also be produced by a geochemical process , volcanic or hydrothermal activity .   The atmosphere is quite dusty , giving the Martian sky a light brown or orange-red color when seen from the surface ; data from the Mars Exploration Rovers indicate suspended particles of roughly 1.5 micrometres in diameter .   On 16 December 2014 , NASA reported detecting an unusual increase , then decrease , in the amounts of methane in the atmosphere of the planet Mars . Organic chemicals have been detected in powder drilled from a rock by the Curiosity rover . Based on deuterium to hydrogen ratio studies , much of the water at Gale Crater on Mars was found to have been lost during ancient times , before the lakebed in the crater was formed ; afterwards , large amounts of water continued to be lost .   On 18 March 2015 , NASA reported the detection of an aurora that is not fully understood and an unexplained dust cloud in the atmosphere of Mars .   On 4 April 2015 , NASA reported studies , based on measurements by the Sample Analysis at Mars ( SAM ) instrument on the Curiosity rover , of the Martian atmosphere using xenon and argon isotopes . Results provided support for a `` vigorous '' loss of atmosphere early in the history of Mars and were consistent with an atmospheric signature found in bits of atmosphere captured in some Martian meteorites found on Earth . This was further supported by results from the MAVEN orbiter circling Mars , that the solar wind is responsible for stripping away the atmosphere of Mars over the years .

Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

Atmosphere of Earth <=SEP=> The atmosphere of Earth is the layer of gases , commonly known as air , that surrounds the planet Earth and is retained by Earth 's gravity . The atmosphere of Earth protects life on Earth by absorbing ultraviolet solar radiation , warming the surface through heat retention ( greenhouse effect ) , and reducing temperature extremes between day and night ( the diurnal temperature variation ) .   By volume , dry air contains 78.09 % nitrogen , 20.95 % oxygen , 0.93 % argon , 0.04 % carbon dioxide , and small amounts of other gases . Air also contains a variable amount of water vapor , on average around 1 % at sea level , and 0.4 % over the entire atmosphere . Air content and atmospheric pressure vary at different layers , and air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth 's troposphere and in artificial atmospheres .   The atmosphere has a mass of about 5.15 kg , three quarters of which is within about 11 km of the surface . The atmosphere becomes thinner and thinner with increasing altitude , with no definite boundary between the atmosphere and outer space . The Kármán line , at 100 km , or 1.57 % of Earth 's radius , is often used as the border between the atmosphere and outer space . Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km . Several layers can be distinguished in the atmosphere , based on characteristics such as temperature and composition .   The study of Earth 's atmosphere and its processes is called atmospheric science ( aerology ) . Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann .

Atmosphere of Venus <=SEP=> The atmosphere of Venus is the layer of gases surrounding Venus . It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth . The temperature at the surface is 740 K ( 467 ° C , 872 ° F ) , and the pressure is 93 bar ( 9.3 MPa ) , roughly the pressure found 900 m underwater on Earth . The Venusian atmosphere supports opaque clouds made of sulfuric acid , making optical Earth-based and orbital observation of the surface impossible . Information about the topography has been obtained exclusively by radar imaging . Aside from carbon dioxide , the other main component is nitrogen . Other chemical compounds are present only in trace amounts .   Mikhail Lomonosov was the first person to hypothesize the existence of an atmosphere on Venus based on his observation of the transit of Venus of 1761 in a small observatory near his house in Saint Petersburg , Russia .   Aside from the very surface layers , the atmosphere is in a state of vigorous circulation . The upper layer of troposphere exhibits a phenomenon of super-rotation , in which the atmosphere circles the planet in just four Earth days , much faster than the planet 's sidereal day of 243 days . The winds supporting super-rotation blow at a speed of 100 m/s ( ~ 360 km/h or 220 mph ) or more . Winds move at up to 60 times the speed of the planet 's rotation , while Earth 's fastest winds are only 10 % to 20 % rotation speed . On the other hand , the wind speed becomes increasingly slower as the elevation from the surface decreases , with the breeze barely reaching the speed of 10 km/h ( 2.8 m/s ) on the surface . Near the poles are anticyclonic structures called polar vortices . Each vortex is double-eyed and shows a characteristic S-shaped pattern of clouds . Above there is an intermediate layer of mesosphere which separates the troposphere from the thermosphere . The thermosphere is also characterized by strong circulation , but very different in its nature - the gases heated and partially ionized by sunlight in the sunlit hemisphere migrate to the dark hemisphere where they recombine and downwell .   Unlike Earth , Venus lacks a magnetic field . Its ionosphere separates the atmosphere from outer space and the solar wind . This ionised layer excludes the solar magnetic field , giving Venus a distinct magnetic environment . This is considered Venus 's induced magnetosphere . Lighter gases , including water vapour , are continuously blown away by the solar wind through the induced magnetotail . It is speculated that the atmosphere of Venus up to around 4 billion years ago was more like that of the Earth with liquid water on the surface . A runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of the levels of other greenhouse gases .   Despite the harsh conditions on the surface , the atmospheric pressure and temperature at about 50 km to 65 km above the surface of the planet is nearly the same as that of the Earth , making its upper atmosphere the most Earth-like area in the Solar System , even more so than the surface of Mars . Due to the similarity in pressure and temperature and the fact that breathable air ( 21 % oxygen , 78 % nitrogen ) is a lifting gas on Venus in the same way that helium is a lifting gas on Earth , the upper atmosphere has been proposed as a location for both exploration and colonization .   On January 29 , 2013 , ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to `` the ion tail seen streaming from a comet under similar conditions . ''