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The Amazonian is a geologic system and time period on the planet Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those on Mars today.〔Tanaka, K.L. (1986). The Stratigraphy of Mars. ''J. Geophys. Res.,'' Seventeenth Lunar and Planetary Science Conference Part 1, ''91''(B13), E139–E158.〕〔Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.〕 The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 3 billion years ago, though error bars on this date are extremely large (~500 million years).〔Werner, S. C., and K. L. Tanaka (2011), Redefinition of the crater-density and absolute-age boundaries for the chronostratigraphic system of Mars, Icarus, 215(2), 603–607, doi:10.1016/j.icarus.2011.07.024.〕 The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Amazonian continues to the present day. ==Description and name origin== The ''Amazonian'' System and Period is named after Amazonis Planitia, which has a sparse crater density over a wide area. Such densities are representative of many Amazonian-aged surfaces. The type area of the Amazonian System is in the Amazonis quadrangle (MC-8) around . ImageSize = width:800 height:50 PlotArea = left:15 right:15 bottom:20 top:5 AlignBars = early Period = from:-4500 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 Colors= id:prenoachicol value:rgb(0.7,0.4,1) id:noachicol value:rgb(0.5,0.5,0.8) id:hespericol value:rgb(1,0.2,0.2) id:amazonicol value:rgb(1,0.5,0.2) PlotData= align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) text:Amazonian from:-3000 till:0 color:amazonicol text:Hesperian from:-3700 till:-3000 color:hespericol text:Noachian from:-4100 till:-3700 color:noachicol text:Pre-Noachian from:start till:-4100 color:prenoachicol 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Amazonian (Mars)」の詳細全文を読む スポンサード リンク
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