Query: The lower temperatures at this "coldest point" have caused global water vapor levels to drop, even as carbon levels rise.

Relevant passages:
Troposphere <=SEP=> The troposphere is the lowest portion of Earth 's atmosphere , and is also where nearly all weather takes place . It contains approximately 75 % of the atmosphere 's mass and 99 % of the total mass of water vapor and aerosols . The average depths of the troposphere are 20 km in the tropics , 17 km in the mid latitudes , and 7 km in the polar regions in winter . The lowest part of the troposphere , where friction with the Earth 's surface influences air flow , is the planetary boundary layer . This layer is typically a few hundred meters to 2 km deep depending on the landform and time of day . Atop the troposphere is the tropopause , which is the border between the troposphere and stratosphere . The tropopause is an inversion layer , where the air temperature ceases to decrease with height and remains constant through its thickness .   The word troposphere derives from the for `` turn , turn toward , trope '' and '' - sphere '' ( as in , the Earth ) , reflecting the fact that rotational turbulent mixing plays an important role in the troposphere 's structure and behaviour . Most of the phenomena associated with day-to-day weather occur in the troposphere .

Water on Mars <=SEP=> Almost all water on Mars today exists as ice , though it also exists in small quantities as vapor in the atmosphere and occasionally as low-volume liquid brines in shallow Martian soil . The only place where water ice is visible at the surface is at the north polar ice cap . Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate latitudes . More than five million cubic kilometers of ice have been identified at or near the surface of modern Mars , enough to cover the whole planet to a depth of 35 meters . Even more ice is likely to be locked away in the deep subsurface .   Some liquid water may occur transiently on the Martian surface today , but only under certain conditions . No large standing bodies of liquid water exist , because the atmospheric pressure at the surface averages just 600 Pa -- about 0.6 % of Earth 's mean sea level pressure -- and because the global average temperature is far too low ( 210 K ) , leading to either rapid evaporation ( sublimation ) or rapid freezing . Before about 3.8 billion years ago , Mars may have had a denser atmosphere and higher surface temperatures , allowing vast amounts of liquid water on the surface , possibly including a large ocean that may have covered one-third of the planet . Water has also apparently flowed across the surface for short periods at various intervals more recently in Mars ' history . On December 9 , 2013 , NASA reported that , based on evidence from the Curiosity rover studying Aeolis Palus , Gale Crater contained an ancient freshwater lake that could have been a hospitable environment for microbial life .   Many lines of evidence indicate that water is abundant on Mars and has played a significant role in the planet 's geologic history . The present-day inventory of water on Mars can be estimated from spacecraft imagery , remote sensing techniques ( spectroscopic measurements , radar , etc. ) , and surface investigations from landers and rovers . Geologic evidence of past water includes enormous outflow channels carved by floods , ancient river valley networks , deltas , and lakebeds ; and the detection of rocks and minerals on the surface that could only have formed in liquid water . Numerous geomorphic features suggest the presence of ground ice ( permafrost ) and the movement of ice in glaciers , both in the recent past and present . Gullies and slope lineae along cliffs and crater walls suggest that flowing water continues to shape the surface of Mars , although to a far lesser degree than in the ancient past .   Although the surface of Mars was periodically wet and could have been hospitable to microbial life billions of years ago , the current environment at the surface is dry and subfreezing , probably presenting an insurmountable obstacle for living organisms . In addition , Mars lacks a thick atmosphere , ozone layer , and magnetic field , allowing solar and cosmic radiation to strike the surface unimpeded . The damaging effects of ionizing radiation on cellular structure is another one of the prime limiting factors on the survival of life on the surface . Therefore , the best potential locations for discovering life on Mars may be in subsurface environments . On November 22 , 2016 , NASA reported finding a large amount of underground ice on the planet Mars -- the volume of water detected is equivalent to the volume of water in Lake Superior .   Understanding water on Mars is vital to assess the planet 's potential for harboring life and for providing usable resources for future human exploration . For this reason , ` Follow the Water ' was the science theme of NASA 's Mars Exploration Program ( MEP ) in the first decade of the 21st century . Discoveries by the 2001 Mars Odyssey , Mars Exploration Rovers ( MERs ) , Mars Reconnaissance Orbiter ( MRO ) , and Mars Phoenix lander have been instrumental in answering key questions about water 's abundance and distribution on Mars . The ESA 's Mars Express orbiter has also provided essential data in this quest . The Mars Odyssey , Mars Express , MER Opportunity rover , MRO , and Mars Science Lander Curiosity rover are still sending back data from Mars , and discoveries continue to be made .

Eocene <=SEP=> The Eocene ( -LSB- pronˈiːəˌsiːn , _ ˈiːoʊ - -RSB- ) Epoch , lasting from , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era . The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch . The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C . The end is set at a major extinction event called the Grande Coupure ( the `` Great Break '' in continuity ) or the Eocene -- Oligocene extinction event , which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay . As with other geologic periods , the strata that define the start and end of the epoch are well identified , though their exact dates are slightly uncertain .   The name Eocene comes from the Ancient Greek ἠώς ( ēṓs , `` dawn '' ) and καινός ( kainós , `` new '' ) and refers to the `` dawn '' of modern ( ` new ' ) fauna that appeared during the epoch .

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 . ''

Snowball Earth <=SEP=> The Snowball Earth hypothesis proposes that Earth 's surface became entirely or nearly entirely frozen at least once , sometime earlier than 650 Mya ( million years ago ) . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical palaeolatitudes , and other enigmatic features in the geological record . Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice - or slush-covered ocean , and emphasize the difficulty of escaping an all-frozen condition . A number of unanswered questions remain , including whether the Earth was a full snowball , or a `` slushball '' with a thin equatorial band of open ( or seasonally open ) water .   The snowball Earth episodes occurred before the sudden radiation of multicellular bioforms , known as the Cambrian explosion . The most recent snowball episode may have triggered the evolution of multicellularity . Another , much earlier and longer snowball episode , the Huronian glaciation , which occurred 2400 to 2100 Mya , may have been triggered by the first appearance of oxygen in the atmosphere , the `` Great Oxygenation Event . ''