Query: Each of the six major past ice ages began when the atmospheric carbon dioxide content was far higher than at present.

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Climate of Mars <=SEP=> The climate of Mars has been an issue of scientific curiosity for centuries , in part because Mars is the only terrestrial planet whose surface can be directly observed in detail from the Earth with help from a telescope .   Although Mars is smaller than the Earth , at 11 % of Earth 's mass , and 50 % farther from the Sun than the Earth , its climate has important similarities , such as the polar ice caps , seasonal changes and the observable presence of weather patterns . It has attracted sustained study from planetologists and climatologists . While Mars 's climate has similarities to Earth 's , including periodic ice ages , there are also important differences , such as much lower thermal inertia . Mars ' atmosphere has a scale height of approximately 11 km , 60 % greater than that on Earth . The climate is of considerable relevance to the question of whether life is or was present on the planet . The climate briefly received more interest in the news due to NASA measurements indicating increased sublimation of the south polar icecap leading to some popular press speculation that Mars was undergoing a parallel bout of global warming , although Mars ' average temperature has actually cooled in recent decades .   Mars has been studied by Earth-based instruments since the 17th century but it is only since the exploration of Mars began in the mid-1960s that close-range observation has been possible . Flyby and orbital spacecraft have provided data from above , while direct measurements of atmospheric conditions have been provided by a number of landers and rovers . Advanced Earth orbital instruments today continue to provide some useful `` big picture '' observations of relatively large weather phenomena .   The first Martian flyby mission was Mariner 4 which arrived in 1965 . That quick two-day pass ( July 14 -- 15 , 1965 ) was limited and crude in terms of its contribution to the state of knowledge of Martian climate . Later Mariner missions ( Mariner 6 , and Mariner 7 ) filled in some of the gaps in basic climate information . Data-based climate studies started in earnest with the Viking program in 1975 and continues with such probes as the Mars Reconnaissance Orbiter .   This observational work has been complemented by a type of scientific computer simulation called the Mars general circulation model . Several different iterations of MGCM have led to an increased understanding of Mars as well as the limits of such models .

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 .

Peat <=SEP=> Peat ( -LSB- piːt -RSB- ) , also called turf ( -LSB- tɜːrf -RSB- ) , is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands , bogs , mires , moors , or muskegs . The peatland ecosystem is the most efficient carbon sink on the planet because peatland plants capture the CO2 which is naturally released from the peat ; this maintains an equilibrium . In natural peatlands , the `` annual rate of biomass production is greater than the rate of decomposition '' , but it takes `` thousands of years for peatlands to develop the deposits of , which is the average depth of the boreal -LSB- northern -RSB- peatlands '' . Sphagnum moss ( peat moss ) is one of the most common components in peat , although many other plants can contribute . Soils that contain mostly peat are known as histosols . Peat forms in wetland conditions , where flooding obstructs flows of oxygen from the atmosphere . This slows rates of decomposition .   Peatlands , particularly bogs , are the most important source of peat . That said , other less common wetland types , including fens , pocosins , and peat swamp forests , also deposit peat . Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss , ericaceous shrubs , and sedges ( see bog for more information on this aspect of peat ) . Because organic matter accumulates over thousands of years , peat deposits also provide records of past vegetation and climates stored in plant remains like pollen . This allows humans to reconstruct past environments and study changes in human land use .   Peat is harvested as an important source of fuel in certain parts of the world . By volume , there are about 4 e12m3 of peat in the world , covering a total of around 2 % of the global land area ( about 3 e6km2 ) , containing about 8 billion terajoules of energy . Over time , the formation of peat is often the first step in the geological formation of other fossil fuels such as coal , particularly low-grade coal such as lignite .

Geologic temperature record <=SEP=> The Geologic temperature record are changes in Earth 's environment as determined from geologic evidence on multi-million to billion ( 109 ) year time scales . The study of past temperatures provides an important paleoenvironmental insight because it is a crucial component of the climate and oceanography of the time .

2012 in science <=SEP=> The year 2012 involved many significant scientific events and discoveries , including the first orbital rendezvous by a commercial spacecraft , the discovery of a particle highly similar to the long-sought Higgs boson , and the near-eradication of guinea worm disease . A total of 72 successful orbital spaceflights occurred in 2012 , and the year also saw numerous developments in fields such as robotics , 3D printing , stem cell research and genetics . Over 540,000 technological patent applications were made in the United States alone in 2012 .   2012 was declared the International Year of Sustainable Energy for All by the United Nations . 2012 also marked Alan Turing Year , a celebration of the life and work of the English mathematician , logician , cryptanalyst and computer scientist Alan Turing .