View source for Noachian

{{short description|Geological system and early time period of Mars}}
{{About|the Martian geologic system and period|the Biblical patriarch of whom "Noachian" is the derived adjective|Noah}}
{{Infobox geologic timespan
| name                         = Noachian
| manual_color                 = rgb(127.0, 127.0, 204.0)
| top_bar                      = mars
| time_start                   = 4100
| time_end                     = 3700
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| image_outcrop                = Noachian Terrain.jpg
| caption_outcrop              = [[Mars Orbital Laser Altimeter|MOLA]] colorized relief map of [[Noachis Terra]], the [[type locality (geology)|type area]] for the Noachian System. Note the superficial resemblance to the [[lunar highlands]]. Colors indicate elevation, with red highest and blue-violet lowest. The blue feature at bottom right is the northwestern portion of the giant [[Hellas Planitia|Hellas]] [[impact crater|impact basin]].
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<!--Chronology-->
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| subdivisions                 = Early Noachian<br/>
Middle Noachian<br/>
Late Noachian
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<!--Etymology-->
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<!--Usage Information-->
| celestial_body               = mars
| usage                        =
| timescales_used              = Martian Geologic Timescale
| used_by                      =
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<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  =
| type_section                 = [[Noachis Terra]]
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The '''Noachian''' is a [[system (stratigraphy)|geologic system]] and early [[geologic timescale|time period]] on the planet [[Mars]] characterized by high rates of [[meteorite]] and [[asteroid]] [[Impact event|impacts]] and the possible presence of abundant [[surface water]].<ref>{{cite news |last=Amos |first=Jonathan |title=Clays in Pacific Lavas Challenge Wet Early Mars Idea |work=[[BBC News]] |date=10 September 2012 |url=https://www.bbc.co.uk/news/science-environment-19525421 }}</ref> The [[absolute age]] of the Noachian period is uncertain but probably corresponds to the lunar [[Pre-Nectarian]] to [[Early Imbrian]] periods<ref name=Tanaka86>{{cite journal | last1 = Tanaka | first1 = K.L. | year = 1986 | title = The Stratigraphy of Mars | url = https://zenodo.org/record/1231412| journal = J. Geophys. Res. | volume = 91 | issue = B13| pages = E139–E158 | doi = 10.1029/JB091iB13p0E139 | bibcode=1986JGR....91E.139T }}</ref> of 4100 to 3700 million years ago, during the interval known as the [[Late Heavy Bombardment]].<ref name=CarrHead10 /> Many of the large impact basins on the [[Moon]] and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth's [[Hadean]] and early [[Archean]] eons when Earth's first life forms likely arose.<ref>{{cite journal | last1 = Abramov | first1 = O. | last2 = Mojzsis | first2 = S.J. | year = 2009 | title = Microbial Habitability of the Hadean Earth During the Late Heavy Bombardment | journal = Nature | volume = 459 | issue = 7245| pages = 419–422 | doi = 10.1038/nature08015 | pmid=19458721 | bibcode = 2009Natur.459..419A| s2cid = 3304147 }}</ref>
Noachian-aged terrains on Mars are prime [[Lander (spacecraft)|spacecraft]] landing sites to search for [[fossil]] evidence of [[extraterrestrial life|life]].<ref>{{cite journal | last1 = Grotzinger | first1 = J | year = 2009 | title = Beyond Water on Mars | journal = Nature Geoscience | volume = 2 | issue = 4| pages = 231–233 | doi = 10.1038/ngeo480 | bibcode = 2009NatGe...2..231G }}</ref><ref>{{cite journal | last1 = Grant | first1 = J.A. | display-authors = etal | year = 2010 | title = The Science Process for Selecting the Landing Site for the 2011 Mars Science Laboratory | url = http://www.geo.utep.edu/pub/hurtado/planetary/lectures/week8/papers2/grant_etal_2010_pss_mslsiteselection.pdf | journal = Planet. Space Sci. | volume =  59| issue = 11–12| pages =  1114–1127| doi = 10.1016/j.pss.2010.06.016 }}</ref><ref>Anderson, R.C.; Dohm, J.M.; Buczkowski, D.; Wyrick, D.Y. (2022). Early Noachian Terrains: Vestiges of the Early Evolution of Mars. ''Icarus,'' '''387,''' 115170.</ref> During the Noachian, the [[atmosphere]] of Mars was denser than it is today, and the climate possibly warm enough (at least episodically) to allow rainfall.<ref name=CraddockHoward02>{{cite journal | last1 = Craddock | first1 = R. A. | last2 = Howard | first2 = A.D. | year = 2002 | title = The Case for Rainfall on a Warm, Wet Early Mars | journal = J. Geophys. Res. | volume = 107 | issue = E11| page = 5111 | doi = 10.1029/2001JE001505 | bibcode=2002JGRE..107.5111C| citeseerx = 10.1.1.485.7566 }}</ref> Large lakes and rivers were present in the southern hemisphere,<ref>{{cite journal | last1 = Malin | first1 = M.C. | last2 = Edgett | first2 = K.S. | year = 2003 | title = Evidence for Persistent Flow and Aqueous Sedimentation on Early Mars | journal = Science | volume = 302 | issue = 5652| pages = 1931–1934 | doi = 10.1126/science.1090544 | pmid=14615547 | bibcode = 2003Sci...302.1931M| s2cid = 39401117 | doi-access = free }}</ref><ref>{{cite journal | last1 = Irwin | first1 = R.P. | display-authors = etal | year = 2002 | title = A Large Paleolake Basin at the Head of Ma'adim Vallis, Mars | journal = Science | volume = 296 | issue = 5576| pages = 2209–12 | doi = 10.1126/science.1071143 | pmid = 12077414 | bibcode = 2002Sci...296.2209R | s2cid = 23390665 }}</ref> and an ocean may have covered the low-lying northern plains.<ref>{{cite journal | last1 = Clifford | first1 = S.M. | last2 = Parker | first2 = T.J. | year = 2001 | title = The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains | journal = Icarus | volume = 154 | issue = 1| pages = 40–79 | doi=10.1006/icar.2001.6671 | bibcode=2001Icar..154...40C}}</ref><ref name=Achille10>{{cite journal | last1 = Di Achille | first1 = G. | last2 = Hynek | first2 = B.M. | year = 2010 | title = Ancient Ocean on Mars Supported by Global Distribution of Deltas and Valleys | journal = Nature Geoscience | volume =  3| issue = 7| pages =  459–463| doi = 10.1038/NGEO891 | bibcode = 2010NatGe...3..459D }}</ref> Extensive [[volcanism]] occurred in the [[Tharsis]] region, building up enormous masses of volcanic material (the [[Tharsis bulge]]) and releasing large quantities of gases into the atmosphere.<ref name=CarrHead10>{{cite journal | last1 = Carr | first1 = M.H. | last2 = Head | first2 = J.W. | year = 2010 | title = Geologic History of Mars | url = https://zenodo.org/record/1258929| journal = Earth Planet. Sci. Lett. | volume = 294 | issue = 3–4| pages = 185–203 | doi =  10.1016/j.epsl.2009.06.042 | bibcode = 2010E&PSL.294..185C}}</ref> [[Weathering]] of surface rocks produced a diversity of [[clay minerals]] ([[phyllosilicates]]) that formed under chemical conditions conducive to [[microorganism|microbial life]].<ref name=Bibring06>{{cite journal | last1 = Bibring | first1 = J.-P. | display-authors = etal   | year = 2006 | title = Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data | journal = Science | volume = 312 | issue = 5772| pages = 400–404 | doi = 10.1126/science.1122659 | pmid=16627738| doi-access =  | bibcode = 2006Sci...312..400B }}</ref><ref>{{cite journal | last1 = Bishop | first1 = J.L. | display-authors = etal   | year = 2008 | title = Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars | url = https://authors.library.caltech.edu/34903/2/Bishop.SOM.pdf| journal = Science | volume = 321 | issue = 5890| pages = 830–833 | doi = 10.1126/science.1159699 | pmid=18687963| pmc = 7007808 | type = Submitted manuscript | bibcode = 2008Sci...321..830B }}</ref>
Although there is abundant geologic evidence for surface water early in Mars history, the nature and timing of the climate conditions under which that water occurred is a subject of vigorous scientific debate.<ref>Wordsworth, R. Ehlmann, B.; Forget, F.; Haberle, R.; Head, J.; Kerber, L. (2018). Healthy Debate on Early Mars (Letter to the Editor). ''Nature Geoscience,'' '''11,''' 888.</ref> Today Mars is a cold, hyperarid desert with an average atmospheric pressure less than 1% that of Earth. Liquid water is unstable and will either freeze or evaporate depending on season and location (See [[Water on Mars]]). Reconciling the geologic evidence of river valleys and lakes with computer climate models of Noachian Mars has been a major challenge.<ref>Kite, E.S. (2019). Geologic Constraints on Early Mars Climate. ''Space Sci. Rev.'' '''215'''(10), https://doi.org/10.1007/s11214-018-0575-5.</ref> Models that posit a thick carbon dioxide atmosphere and consequent [[greenhouse effect]] have difficulty reproducing the higher mean temperatures necessary for abundant liquid water. This is partly because Mars receives less than half the solar radiation that Earth does and because the sun during the Noachian was only about 75% as bright as it is today.<ref>Wordsworth, R. et al. (2013). Global Modelling of the Early Martian Climate under a Denser CO<sub>2</sub> Atmosphere: Water Cycle and Ice Evolution. ''Icarus,'' '''222,''' 1–19.</ref><ref>Gough, D. O. (1981). Solar interior structure and luminosity variations. ''Solar Physics,'' '''74'''(1), 21–34. https://doi.org/10.1007/BF00151270.</ref> As a consequence, some researchers now favor an overall Noachian climate that was “cold and icy” punctuated by brief (hundreds to thousands of years) climate excursions warm enough to melt surface ice and produce the fluvial features seen today.<ref>Fastook, J. L.,; Head, J. W. (2015). Glaciation in the Late Noachian Icy Highlands: Ice Accumulation, Distribution, Flow Rates, Basal Melting, and Top-Down Melting Rates and Patterns. ''Planetary and Space Science,'' '''106,''' 82–98. https://doi.org/10.1016/j.pss.2014.11.028</ref> Other researchers argue for a semiarid early Mars with at least transient periods of rainfall warmed by a carbon dioxide-hydrogen atmosphere.<ref>Ramirez, R.M.; Craddock, R.A. (2018). The Geological and Climatological Case for a Warmer and Wetter Early Mars. ''Nature Geoscience,'' '''11,''' 230–237.</ref> Causes of the warming periods remain unclear but may be due to large impacts, volcanic eruptions, or [[orbital forcing]]. In any case it seems probable that the climate throughout the Noachian was not uniformly warm and wet.<ref>Wordsworth, R. (2016). The Climate of Early Mars. ''Annu. Rev. Earth Planet. Sci.,'' '''44,''' 381–408.</ref> In particular, much of the river- and lake-forming activity appears to have occurred over a relatively short interval at the end of the Noachian and extending into the early [[Hesperian]].<ref> Howard, A.D.; Moore, J.M.; Irwin, R.P. (2005). An Intense Terminal Epoch of Widespread Fluvial Activity on Early Mars: 1. Valley Network Incision and Associated Deposits. ''J. Geophys. Res.,'' '''110,''' E12S14, doi:10.1029/2005JE002459.</ref><ref>Fassett, C.I.; Head, J.W. (2008a). The Timing of Martian Valley Network Activity: Constraints from Buffered Crater Counting. ''Icarus,'' '''195,''' 61–89.</ref><ref>Fassett, C.I.; Head, J.W. (2008b). Valley Network-Fed, Open-Basin Lakes on Mars: Distribution and Implications for Noachian Surface and Subsurface Hydrology. ''Icarus,'' '''198,''' 37–56.</ref>
==Description and name origin==
The ''Noachian'' System and Period is named after [[Noachis Terra]] (lit. "Land of [[Noah]]"), a heavily cratered highland region west of the [[Hellas Planitia|Hellas]] basin. The [[Type locality (geology)|type area]] of the Noachian System is in the [[Noachis quadrangle]] (MC-27) around {{Coord|40|S|340|W|globe:Mars}}.<ref name=Tanaka86 /> At a large scale (>100 m), Noachian surfaces are very hilly and rugged, superficially resembling the [[lunar highlands]]. Noachian terrains consist of overlapping and interbedded [[ejecta blanket]]s of many old craters. Mountainous rim materials and uplifted [[Basement (geology)|basement rock]] from large impact basins are also common.<ref name=ScottCarr78 /> (See [[Anseris Mons]], for example.) The number-density of large impact craters is very high, with about 200 craters greater than 16&nbsp;km in diameter per million km<sup>2</sup>.<ref>Werner, S.C.; Tanaka, K.L. (2011). Redefinition of the Crater-Density and Absolute-Age Boundaries for the Chronostratigraphic System of Mars. ''Icarus,'' '''215,''' 603–607.</ref> Noachian-aged units cover 45% of the Martian surface;<ref name=Tanaka14>Tanaka, K.L. et al. (2014). Geologic Map of Mars. U.S. Geological Survey Scientific Investigations Map 3292, pamphlet</ref> they occur mainly in the southern highlands of the planet, but are also present over large areas in the north, such as in [[Tempe Terra|Tempe]] and [[Xanthe Terra|Xanthe]] Terrae, [[Acheron Fossae]], and around the Isidis basin ([[Libya Montes]]).<ref>Scott, D.H.; Tanaka, K.L. (1986). Geologic Map of the Western Equatorial Region of Mars. U.S. Geological Survey Miscellaneous Investigations Series Map I–1802–A.</ref><ref>Greeley, R.; Guest, J.E. (1987). Geologic Map of the Eastern Equatorial Region of Mars. U.S. Geological Survey Miscellaneous Investigations Series Map I–1802–B.</ref>
{{Mars timescale}}{{center|<small>[[Geological history of Mars|Martian Time Periods (Millions of Years Ago)]]</small>}}
==Noachian [[chronology]] and [[stratigraphy]]==
[[File:Mars Cross Section.tif|right|thumb|upright=1.4|Schematic cross section of image at left. Surface units are interpreted as a sequence of layers ([[stratum|strata]]), with the youngest at top and oldest at bottom in accordance with the [[law of superposition]].]]
[[Image:Lava flow and crater ejecta.JPG|left|thumb|[[HiRISE]] image illustrating [[Law of superposition|superpositioning]], a principle that lets geologists determine the relative ages of surface units. The dark-toned lava flow overlies (is younger than) the light-toned, more heavily cratered terrain (older lava flow?) at right. The ejecta of the crater at center overlies both units, indicating that the crater is the youngest feature in the image. (See schematic cross section, right.)]]
Martian time periods are based on [[geologic map]]ping of surface units from [[Remote sensing|spacecraft images]].<ref name=ScottCarr78>Scott, D.H.; Carr, M.H. (1978). Geologic Map of Mars. U.S. Geological Survey Miscellaneous  Investigations Series Map I-1083.</ref><ref>McCord, T.M. ''et al.'' (1980). Definition and Characterization of Mars Global Surface Units: Preliminary Unit Maps. 11th Lunar and Planetary Science Conference: Houston: TX, abstract #1249, pp. 697–699.  http://www.lpi.usra.edu/meetings/lpsc1980/pdf/1249.pdf.</ref> A surface unit is a terrain with a distinct texture, color, [[albedo]], [[Thermal infrared spectroscopy|spectral]] property, or set of landforms that distinguish it from other surface units and is large enough to be shown on a map.<ref>Greeley, R. (1994) ''Planetary Landscapes,'' 2nd ed.; Chapman & Hall: New York, p. 8 and Fig. 1.6.</ref> Mappers use a [[stratigraphy|stratigraphic]] approach pioneered in the early 1960s for photogeologic studies of the [[Geology of the Moon|Moon]].<ref>See Mutch, T.A. (1970). ''Geology of the Moon: A Stratigraphic View;'' Princeton University Press: Princeton, NJ, 324 pp. and Wilhelms, D.E. (1987). ''The Geologic History of the Moon,'' USGS Professional Paper 1348; http://ser.sese.asu.edu/GHM/ for reviews of this topic.</ref> Although based on surface characteristics, a surface unit is not the surface itself or group of [[landform]]s. It is an ''inferred'' [[geological unit|geologic unit]] (e.g., [[Formation (stratigraphy)|formation]]) representing a sheetlike, wedgelike, or tabular body of rock that underlies the surface.<ref>Wilhelms, D.E. (1990). Geologic Mapping in ''Planetary Mapping,'' R. Greeley, R.M. Batson, Eds.; Cambridge University Press: Cambridge UK, p. 214.</ref><ref name=Tanaka92>Tanaka, K.L.; Scott, D.H.; Greeley, R. (1992). Global Stratigraphy in ''Mars,'' H.H. Kieffer ''et al.,'' Eds.; University of Arizona Press: Tucson, AZ, pp. 345–382.</ref> A surface unit may be a crater ejecta deposit, lava flow, or any surface that can be represented in three dimensions as a discrete [[stratum]] bound above or below by adjacent units (illustrated right). Using principles such as [[Law of superposition|superpositioning]] (illustrated left), [[cross-cutting relationships]], and the relationship of [[Geology of Mars#Geologic history|impact crater density]] to age, geologists can place the units into a [[relative dating|relative age]] sequence from oldest to youngest. Units of similar age are grouped globally into larger, time-stratigraphic ([[Chronostratigraphy|chronostratigraphic]]) units, called [[System (stratigraphy)|systems]]. For Mars, four systems are defined: the Pre-Noachian, Noachian, [[Hesperian (Mars)|Hesperian]], and Amazonian. Geologic units lying below (older than) the Noachian are informally designated [[Pre-Noachian]].<ref name=NimmoTanaka05>{{cite journal | last1 = Nimmo | first1 = F. | last2 = Tanaka | first2 = K. | year = 2005 | title = Early Crustal Evolution of Mars  | journal = Annu. Rev. Earth Planet. Sci. | volume = 33 | pages = 133–161 | doi=10.1146/annurev.earth.33.092203.122637 | bibcode = 2005AREPS..33..133N}}</ref> The geologic time ([[geochronology|geochronologic]]) equivalent of the Noachian System is the Noachian Period. Rock or surface units of the Noachian System were formed or deposited during the Noachian Period.
===System vs. Period===
{{Stratigraphy-Mars}}
''System'' and ''Period'' are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system is an idealized stratigraphic [[Geologic record|column]] based on the physical rock record of a [[Type locality (geology)|type area]] (type section) correlated with rocks sections from many different locations planetwide.<ref name=EicherMcAlester80>Eicher, D.L.; McAlester, A.L. (1980). ''History of the Earth;'' Prentice-Hall: Englewood Cliffs, NJ, pp 143–146, {{ISBN|0-13-390047-9}}.</ref> A system is bound above and below by [[stratum|strata]] with distinctly different characteristics (on Earth, usually [[index fossil]]s) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (See [[Cretaceous–Paleogene boundary]] as example.)
At any location, rock sections in a given system are apt to contain gaps ([[unconformity|unconformities]]) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the [[Cretaceous]] System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus, a geologic period represents the time interval over which the [[stratum|strata]] of a system were deposited, including any unknown amounts of time present in gaps.<ref name=EicherMcAlester80 /> Periods are measured in years, determined by [[radioactive dating]]. On Mars, radiometric ages are not available except from [[Martian meteorites]] whose [[provenance]] and stratigraphic context are unknown. Instead, [[absolute age]]s on Mars are determined by impact crater density, which is heavily dependent upon [[Scientific modelling|models]] of crater formation over time.<ref>{{Cite book | last1 = Masson | first1 = P. | last2 = Carr | first2 = M.H. | last3 = Costard | first3 = F. | last4 = Greeley | first4 = R. | last5 = Hauber | first5 = E. | last6 = Jaumann | first6 = R. | title = Chronology and Evolution of Mars | chapter = Geomorphologic Evidence for Liquid Water | year = 2001 | journal = Space Science Reviews | volume = 96 | page = 352 | doi=10.1007/978-94-017-1035-0_12| series = Space Sciences Series of ISSI | bibcode = 2001cem..book..333M | isbn = 978-90-481-5725-9 }}</ref> Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3.<ref name=NimmoTanaka05 /><ref>Hartmann, W.K.; Neukum, G. (2001). Cratering Chronology and Evolution of Mars. In Chronology and Evolution of Mars, Kallenbach, R. ''et al.'' Eds., ''Space Science Reviews,'' '''96:''' 105–164.</ref>
[[Image:Ridged Plains Overlying Noachian.jpg|right|thumb|Geologic contact of Noachian and Hesperian Systems. Hesperian ridged plains (Hr) embay and overlie older Noachian cratered plains (Npl). Note that the ridged plains partially bury many of the old Noachian-aged craters. Image is [[Thermal Emission Imaging System|THEMIS]] IR mosaic, based on similar [[Viking program|Viking]] photo shown in Tanaka ''et al.'' (1992), Fig. 1a, p. 352.]]
===Boundaries and subdivisions===
Across many areas of the planet, the top of the Noachian System is overlain by more sparsely cratered, ridged plains materials interpreted to be vast [[flood basalt]]s similar in makeup to the [[lunar maria]]. These ridged plains form the base of the younger Hesperian System (pictured right). The lower stratigraphic boundary of the Noachian System is not formally defined. The system was conceived originally to encompass rock units dating back to the formation of the crust 4500 million years ago.<ref name=ScottCarr78 /> However, work by Herbert Frey and colleagues at NASA's [[Goddard Spaceflight Center]] using [[Mars Orbital Laser Altimeter]] (MOLA) data indicates that the southern highlands of Mars contain numerous buried impact basins (called quasi-circular depressions, or QCDs) that are older than the visible Noachian-aged surfaces and that pre-date the Hellas impact. He suggests that the Hellas impact should mark the base of the Noachian System. If Frey is correct, then much of the bedrock in the Martian highlands is pre-Noachian in age, dating back to over 4100&nbsp;million years ago.<ref>Frey, H.V. (2003). Buried Impact Basins and the Earliest History of Mars. Sixth International Conference on Mars, Abstract #3104. http://www.lpi.usra.edu/meetings/sixthmars2003/pdf/3104.pdf.</ref>
The Noachian System is subdivided into three chronostratigraphic [[Series (stratigraphy)|series]]: Lower Noachian, Middle Noachian, and Upper Noachian. The series are based on ''referents'' or locations on the planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, the referent for the Upper Noachian is an area of smooth intercrater plains east of the [[Argyre Planitia|Argyre]] basin. The plains overlie (are younger than) the more rugged cratered terrain of the Middle Noachian and underlie (are older than) the less cratered, ridged plains of the Lower Hesperian Series.<ref name=Tanaka86 /><ref name=Masson90>{{cite journal | last1 = Masson | first1 = P | year = 1991 | title = The Martian Stratigraphy—Short Review and Perspectives | journal = Space Science Reviews | volume = 56 | issue = 1–2| pages = 9–12 | doi=10.1007/bf00178385| bibcode = 1991SSRv...56....9M | s2cid = 121719547 }}</ref> The corresponding geologic time (geochronological) units of the three Noachian series are the Early Noachian, Mid Noachian, and Late Noachian [[Epoch (geology)|Epochs]]. Note that an epoch is a subdivision of a period; the two terms are not synonymous in formal stratigraphy.
<timeline>
ImageSize = width:800 height:50
PlotArea = left:15 right:15 bottom:20 top:5
AlignBars = early
Period = from:-4100 till:-3700
TimeAxis = orientation:horizontal
ScaleMajor = unit:year increment:100 start:-4100
ScaleMinor = unit:year increment:10 start:-4100
Colors=
id:Enoachicol value:rgb(0.5,0.5,0.8)
id:Mnoachicol value:rgb(0.6,0.6,0.9)
id:Lnoachicol value:rgb(0.7,0.7,1)
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align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5)
text:Late_Noachian from:-3840 till:-3700 color:Lnoachicol
text:Mid_Noachian from:-3950 till:-3840 color:Mnoachicol
text:Early_Noachian from:start till:-3950 color:Enoachicol
</timeline>
{{center|<small>Noachian Epochs (Millions of Years Ago)</small><ref name=NimmoTanaka05 />}}
Stratigraphic terms are often confusing to geologists and non-geologists alike. One way to sort through the difficulty is by the following example: You can easily go to [[Cincinnati, Ohio]] and visit a rock [[outcrop]] in the Upper [[Ordovician]] ''Series'' of the Ordovician ''System.'' You can even collect a fossil [[trilobite]] there. However, you cannot visit the Late Ordovician ''Epoch'' in the Ordovician ''Period'' and collect an actual trilobite.
The Earth-based scheme of formal stratigraphic nomenclature has been successfully applied to Mars for several decades now but has numerous flaws. The scheme will no doubt become refined or replaced as more and better data become available.<ref>Tanaka, K.L. (2001). The Stratigraphy of Mars: What We Know, Don't Know, and Need to Do. 32nd Lunar and Planetary Science Conference, Abstract #1695. http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1695.pdf.</ref> (See mineralogical timeline below as example of alternative.) Obtaining radiometric ages on samples from identified surface units is clearly necessary for a more complete understanding of Martian history and chronology.<ref>Carr, 2006, p. 41.</ref>
==Mars during the Noachian Period==
[[Image:AncientMars.jpg|left|thumb|Artist's impression of an early wet Mars. Late Hesperian features (outflow channels) are shown, so this does not present an accurate picture of Noachian Mars, but the overall appearance of the planet from space may have been similar. In particular, note the presence of a large ocean in the northern hemisphere (upper left) and a sea covering [[Hellas Planitia]] (lower right).]]
The Noachian Period is distinguished from later periods by high rates of impacts, erosion, valley formation, volcanic activity, and weathering of surface rocks to produce abundant [[phyllosilicate]]s ([[clay mineral]]s). These processes imply a wetter global climate with at least episodic warm conditions.<ref name=CarrHead10 />
===Impact cratering===
The lunar cratering record suggests that the rate of impacts in the Inner Solar System 4000&nbsp;million years ago was 500 times higher than today.<ref>Carr, 2006, p. 23.</ref> During the Noachian, about one 100-km diameter crater formed on Mars every million years,<ref name=CarrHead10 /> with the rate of smaller impacts exponentially higher.{{efn|reference=The size-distribution of Earth-crossing asteroids greater than 100 m in diameter follows an inverse power-law curve of form N = kD<sup>−2.5</sup>, where N is the number of asteroids larger than diameter D.<ref>Carr, 2006, p. 24.</ref> Asteroids with smaller diameters are present in much greater numbers than asteroids with large diameters.}} Such high impact rates would have fractured the [[crust (geology)|crust]] to depths of several kilometers<ref>{{cite journal | last1 = Davis | first1 = P.A. | last2 = Golombek | first2 = M.P. | year = 1990 | title = Discontinuities in the Shallow Martian Crust at Lunae, Syria, and Sinai Plana | journal = J. Geophys. Res. | volume = 95 | issue = B9| pages = 14231–14248 | doi=10.1029/jb095ib09p14231 | bibcode=1990JGR....9514231D}}</ref> and left thick [[ejecta]] deposits across the planet's surface. Large impacts would have profoundly affected the climate by releasing huge quantities of hot ejecta that heated the atmosphere and surface to high temperatures.<ref>{{cite journal | last1 = Segura | first1 = T.L. | display-authors = etal   | year = 2002 | title = Environmental Effects of Large Impacts on Mars | journal = Science | volume = 298 | issue = 5600| pages = 1977–1980 | doi = 10.1126/science.1073586 | pmid=12471254| bibcode = 2002Sci...298.1977S | s2cid = 12947335 }}</ref> High impact rates probably played a role in removing much of Mars’ early atmosphere through impact erosion.<ref>{{cite journal | last1 = Melosh | first1 = H.J. | last2 = Vickery | first2 = A.M. | year = 1989 | title = Impact Erosion of the Primordial Martian Atmosphere | journal = Nature | volume = 338 | issue = 6215| pages = 487–489 | doi=10.1038/338487a0 | pmid=11536608 | bibcode = 1989Natur.338..487M| s2cid = 4285528 }}</ref>
[[Image:Branched Channels from Viking.jpg|right|thumb|Branched valley network of [[Warrego Valles]] ([[Thaumasia quadrangle]]), as seen by Viking Orbiter. Valley networks like this provide some of the strongest evidence that surface runoff occurred on early Mars.<ref>Carr, 2006, p. 138, Fig. 6.23.</ref>]]
By analogy with the Moon, frequent impacts produced a zone of fractured [[bedrock]] and [[breccia]]s in the upper crust called the [[regolith|megaregolith]].<ref name=Squyresetal92>Squyres, S.W.; Clifford, S.M.; Kuzmin, R.O.; Zimbelman, J.R.; Costard, F.M. (1992). Ice in the Martian Regolith in ''Mars,'' H.H. Kieffer ''et al.,'' Eds.; University of Arizona Press: Tucson, AZ, pp. 523–554.</ref> The high [[porosity]] and [[permeability (earth sciences)|permeability]] of the megaregolith permitted the deep infiltration of [[groundwater]]. Impact-generated heat reacting with the groundwater produced long-lived [[hydrothermal]] systems that could have been exploited by [[thermophilic]] [[microorganisms]], if any existed.<ref>Abramov, O.; Mojzsis, S.J. (2016). Thermal Effects of Impact Bombardments on Noachian Mars. ''Earth Planet. Sci. Lett.,'' '''442,''' 108–120.</ref> Computer models of heat and fluid transport in the ancient Martian crust suggest that the lifetime of an impact-generated hydrothermal system could be hundreds of thousands to millions of years after impact.<ref>{{cite journal | last1 = Abramov | first1 = O. | last2 = Kring | first2 = D.A. | year = 2005 | title = Impact-Induced Hydrothermal Activity on Early Mars | journal = J. Geophys. Res. | volume = 110 | issue = E12| page = E12S09 | doi = 10.1029/2005JE002453 | bibcode=2005JGRE..11012S09A| doi-access = free }}</ref>
===Erosion and valley networks===
Most large Noachian craters have a worn appearance, with highly eroded rims and sediment-filled interiors. The degraded state of Noachian craters, compared with the nearly pristine appearance of Hesperian craters only a few hundred million years younger, indicates that erosion rates were higher (approximately 1000 to 100,000 times<ref>Golombek, M.P.; Bridges, N.T. (2000). Climate Change on Mars Inferred from Erosion Rates at the Mars Pathfinder Landing Site. Fifth International Conference on Mars, 6057.</ref>) in the Noachian than in subsequent periods.<ref name=CarrHead10 /> The presence of partially eroded (etched) terrain in the southern highlands indicates that up to 1&nbsp;km of material was eroded during the Noachian Period. These high erosion rates, though still lower than average terrestrial rates, are thought to reflect wetter and perhaps warmer environmental conditions.<ref name=Andrews-Hanna11>{{cite journal | last1 = Andrews | last2 = Hanna | first2 = J. C. | last3 = Lewis | first3 = K. W. | year = 2011 | title = Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs | journal = J. Geophys. Res. | volume = 116 | issue = E2| page = E02007 | doi = 10.1029/2010JE003709 | bibcode=2011JGRE..116.2007A| doi-access = free }}</ref>
The high erosion rates during the Noachian may have been due to [[Precipitation (meteorology)|precipitation]] and [[surface runoff]].<ref name =CraddockHoward02 /><ref>{{cite journal | last1 = Craddock | first1 = R.A. | last2 = Maxwell | first2 = T.A. | year = 1993 | title = Geomorphic Evolution of the Martian Highlands through Ancient Fluvial Processes | journal = J. Geophys. Res. | volume = 98 | issue = E2| pages = 3453–3468 | doi=10.1029/92je02508 | bibcode=1993JGR....98.3453C}}</ref> Many (but not all) Noachian-aged terrains on Mars are densely dissected by [[Valley networks (Mars)|valley networks]].<ref name=CarrHead10 /> Valley networks are branching systems of valleys that superficially resemble terrestrial river [[drainage basin]]s. Although their principal origin (rainfall erosion, [[groundwater sapping]], or snow melt) is still debated, valley networks are rare in subsequent Martian time periods, indicating unique climatic conditions in Noachian times.
At least two separate phases of valley network formation have been identified in the southern highlands. Valleys that formed in the Early to Mid Noachian show a dense, well-integrated pattern of tributaries that closely resemble [[Drainage system (geomorphology)|drainage patterns]] formed by rainfall in desert regions of Earth. Younger valleys from the Late Noachian to Early Hesperian commonly have only a few stubby tributaries with interfluvial regions (upland areas between tributaries) that are broad and undissected. These characteristics suggest that the younger valleys were formed mainly by [[groundwater sapping]]. If this trend of changing valley morphologies with time is real, it would indicate a change in climate from a relatively wet and warm Mars, where rainfall was occasionally possible, to a colder and more arid world where rainfall was rare or absent.<ref>{{cite journal | last1 = Harrison | first1 = K. P. | last2 = Grimm | first2 = R.E. | year = 2005 | title = Groundwater-Controlled Valley Networks and the Decline of Surface Runoff on Early Mars | journal = J. Geophys. Res. | volume = 110 | issue = E12| page = E12S16 | doi = 10.1029/2005JE002455 | bibcode=2005JGRE..11012S16H| doi-access = free }}</ref>
===Lakes and oceans===
{{further|Water on Mars}}
[[Image:Eberswalde. Delta.jpg|right|thumb|Delta in Eberswalde Crater, seen by [[Mars Global Surveyor]].]]
[[Image:Gale Sediment Layers PIA12508.jpg|right|thumb|Layers of phyllosilicates and sulfates exposed in sediment mound within Gale Crater ([[HiRISE]]).]]
Water draining through the valley networks ponded in the low-lying interiors of craters and in the regional hollows between craters to form large lakes. Over 200 Noachian lake beds have been identified in the southern highlands, some as large as [[Lake Baikal]] or the [[Caspian Sea]] on Earth.<ref>{{cite journal | last1 = Fassett | first1 = C.I. | last2 = Head | first2 = J.W. | year = 2008 | title = Valley Network-Fed, Open-Basin Lakes on Mars: Distribution and Implications for Noachian Surface and Subsurface Hydrology | journal = Icarus | volume = 198 | issue = 1| pages = 37–56 | doi=10.1016/j.icarus.2008.06.016 | bibcode=2008Icar..198...37F| citeseerx = 10.1.1.455.713 }}</ref> Many Noachian craters show channels entering on one side and exiting on the other. This indicates that large lakes had to be present inside the crater at least temporarily for the water to reach a high enough level to breach the opposing crater rim. [[River delta|Deltas]] or [[alluvial fan|fans]] are commonly present where a valley enters the crater floor. Particularly striking examples occur in [[Eberswalde Crater]], [[Holden (Martian crater)|Holden Crater]], and in [[Nili Fossae]] region ([[Jezero (crater)|Jezero Crater]]). Other large craters (e.g., [[Gale (crater)|Gale Crater]]) show finely layered, interior deposits or mounds that probably formed from sediments deposited on lake bottoms.<ref name=CarrHead10 />
Much of the northern hemisphere of Mars lies about 5&nbsp;km lower in elevation than the southern highlands.<ref>Carr, 2006, p. 160.</ref> This [[Martian dichotomy|dichotomy]] has existed since the Pre-Noachian.<ref>Carr, 2006, p. 78.</ref> Water draining from the southern highlands during the Noachian would be expected to pool in the northern hemisphere, forming an ocean (Oceanus Borealis<ref>{{cite journal | last1 = Baker | first1 = V. R. | last2 = Strom | first2 = R. G. | last3 = Gulick | first3 = V. C. | last4 = Kargel | first4 = J. S. | last5 = Komatsu | first5 = G. | year = 1991 | title = Ancient Oceans, Ice Sheets and the Hydrological Cycle on Mars | journal = Nature | volume = 352 | issue = 6336| pages = 589–594 | doi=10.1038/352589a0 | bibcode=1991Natur.352..589B| s2cid = 4321529 }}</ref>). Unfortunately, the existence and nature of a Noachian ocean remains uncertain because subsequent geologic activity has erased much of the [[Geomorphology|geomorphic]] evidence.<ref name=CarrHead10 /> The traces of several possible Noachian- and Hesperian-aged shorelines have been identified along the dichotomy boundary,<ref>{{cite journal | last1 = Parker | first1 = T. J. | last2 = Saunders | first2 = R. S. | last3 = Schneeberger | first3 = D. M. | year = 1989 | title = Transitional Morphology in the West Deuteronilus Mensae Region of Mars: Implications for Modification of the Lowland/Upland Boundary | journal = Icarus | volume = 82 | issue = 1| pages = 111–145 | doi=10.1016/0019-1035(89)90027-4 | bibcode=1989Icar...82..111P}}</ref><ref>{{cite journal | last1 = Fairén | first1 = A. G. | last2 = Dohm | first2 = J. M. | last3 = Baker | first3 = V. R. | last4 = de Pablo | first4 = M. A. | last5 = Ruiz | first5 = J. | last6 = Ferris | first6 = J. | last7 = Anderson | first7 = R. M. | year = 2003 | title = Episodic flood inundations of the northern plains of Mars | url = http://eprints.ucm.es/10431/1/9-Marte_3.pdf| journal = Icarus | volume = 165 | issue = 1| pages = 53–67 | doi=10.1016/s0019-1035(03)00144-1 | bibcode = 2003Icar..165...53F}}</ref> but this evidence has been challenged.<ref>{{cite journal | last1 = Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 1999 | title = Oceans or Seas in the Martian Northern Lowlands: High Resolution Imaging Tests of Proposed Coastlines | journal = Geophys. Res. Lett. | volume = 26 | issue = 19| pages = 3049–3052 | doi=10.1029/1999gl002342 | bibcode=1999GeoRL..26.3049M| doi-access = free }}</ref><ref>{{cite journal | last1 = Ghatan | first1 = G. J. | last2 = Zimbelman | first2 = J. R. | year = 2006  | title = Paucity of Candidate Coastal Constructional Landforms Along Proposed Shorelines on Mars: Implications for a Northern Lowlands-Filling Ocean | journal = Icarus | volume = 185 | issue = 1| pages = 171–196 | doi=10.1016/j.icarus.2006.06.007 | bibcode=2006Icar..185..171G}}</ref> [[Paleoshorelines]] mapped within [[Hellas Planitia]], along with other geomorphic evidence, suggest that large, ice-covered lakes or a sea covered the interior of the Hellas basin during the Noachian period.<ref>{{cite journal | last1 = Moore | first1 = J.M. | last2 = Wilhelms | first2 = D.E. | year = 2001 | title = Hellas as a Possible Site of Ancient Ice-Covered Lakes on Mars | journal = Icarus | volume = 154 | issue = 2| pages = 258–276 | doi=10.1006/icar.2001.6736 | bibcode=2001Icar..154..258M| hdl = 2060/20020050249 | hdl-access = free }}</ref> In 2010, researchers used the global distribution of deltas and valley networks to argue for the existence of a Noachian shoreline in the northern hemisphere.<ref name=Achille10 /> Despite the paucity of geomorphic evidence, if Noachian Mars had a large inventory of water and warm conditions, as suggested by other lines of evidence, then large bodies of water would have almost certainly accumulated in regional lows such as the northern lowland basin and Hellas.<ref name=CarrHead10 />
===Volcanism===
The Noachian was also a time of intense volcanic activity, most of it centered in the [[Tharsis]] region.<ref name=CarrHead10 /> The bulk of the Tharsis bulge is thought to have accumulated by the end of the Noachian Period.<ref>{{cite journal | last1 = Phillips | first1 = R.J. | display-authors = etal   | year = 2001 | title = Ancient Geodynamics and Global-Scale Hydrology on Mars | journal = Science | volume = 291 | issue = 5513| pages = 2587–2591 | doi=10.1126/science.1058701 | pmid=11283367 | bibcode = 2001Sci...291.2587P| s2cid = 36779757 }}</ref> The growth of Tharsis probably played a significant role in producing the planet's atmosphere and the weathering of rocks on the surface. By one estimate, the Tharsis bulge contains around 300 million km<sup>3</sup> of igneous material. Assuming the magma that formed Tharsis contained [[carbon dioxide]] (CO<sub>2</sub>) and water vapor in percentages comparable to that observed in Hawaiian [[basalt]]ic [[lava]], then the total amount of gases released from Tharsis [[magma]]s could have produced a 1.5-bar CO<sub>2</sub> atmosphere and a global layer of water 120 m deep.<ref name=CarrHead10 />
[[File:Noachian Clays PIA11732.jpg|right|thumb|upright=1.35|Four outcroppings of Lower Noachian rocks showing spectral signatures of mineral alteration by water. ([[CRISM]] and [[HiRISE]] images from the [[Mars Reconnaissance Orbiter]])]]
Extensive [[volcanism]] also occurred in the cratered highlands outside of the Tharsis region, but little [[geomorphology|geomorphologic]] evidence remains because surfaces have been intensely reworked by impact.<ref name=CarrHead10 /> [[Infrared spectrometry|Spectral]] evidence from orbit indicates that highland rocks are primarily [[basalt]]ic in composition, consisting of the [[mineral]]s [[pyroxene]], [[plagioclase feldspar]], and [[olivine]].<ref>{{cite journal | last1 = Mustard | first1 = J.F. | display-authors = etal   | year = 2005 | title = Olivine and Pyroxene Diversity in the Crust of Mars | journal = Science | volume = 307 | issue = 5715| pages = 1594–1597 | doi=10.1126/science.1109098| pmid = 15718427 | bibcode = 2005Sci...307.1594M | s2cid = 15548016 | doi-access = free }}</ref> Rocks examined in the [[Columbia Hills (Mars)|Columbia Hills]] by the [[Mars Exploration Rover]] (MER) [[Spirit rover|''Spirit'']] may be typical of Noachian-aged highland rocks across the planet.<ref>Carr, 2006, p. 16-17.</ref> The rocks are mainly degraded [[basalt]]s with a variety of textures indicating severe fracturing and [[breccia]]tion from impact and alteration by hydrothermal fluids. Some of the Columbia Hills rocks may have formed from [[pyroclastic flows]].<ref name=CarrHead10 />
===Weathering products===
The abundance of olivine in Noachian-aged rocks is significant because olivine rapidly weathers to [[clay mineral]]s ([[phyllosilicate]]s) when exposed to water. Therefore, the presence of olivine suggests that prolonged water erosion did not occur globally on early Mars. However, spectral and stratigraphic studies of Noachian [[outcrop]]pings from orbit indicate that olivine is mostly restricted to rocks of the Upper (Late) Noachian Series.<ref name=CarrHead10 /> In many areas of the planet (most notably [[Nili Fossae]] and [[Mawrth Vallis]]), subsequent erosion or impacts have exposed older Pre-Noachian and Lower Noachian units that are rich in phyllosilicates.<ref>Carter J.; Poulet F.; Ody A.; Bibring J.-P.; Murchie S. (2011). Global Distribution, Composition and Setting of Hydrous Minerals on Mars: A Reappraisal. 42nd Lunar and Planetary Science Conference, LPI: Houston, TX, abstract #2593. http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2593.pdf.</ref><ref>{{cite journal | last1 = Rogers | first1 = A. D. | last2 = Fergason | first2 = R.L. | year = 2011 | title = Regional-Scale Stratigraphy of Surface Units in Tyrrhena and Iapygia Terrae, Mars: Insights into Highland Crustal Evolution and Alteration History | journal = J. Geophys. Res. | volume = 116 | issue = E8| page = E08005 | doi = 10.1029/2010JE003772 | bibcode=2011JGRE..116.8005R| doi-access = free }}</ref> Phyllosilicates require a water-rich, [[alkaline]] environment to form. In 2006, researchers using the OMEGA instrument on the [[Mars Express]] spacecraft proposed a new Martian era called the Phyllocian, corresponding to the Pre-Noachian/Early Noachian in which surface water and [[Aqueous solution|aqueous]] weathering was common. Two subsequent eras, the Theiikian and Siderikian, were also proposed.<ref name=Bibring06 /> The Phyllocian era correlates with the age of early valley network formation on Mars. It is thought that deposits from this era are the best candidates in which to search for evidence of past life on the planet.
<timeline>
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:sidericol  value:rgb(1,0.4,0.3)
id:theiicol value:rgb(1,0.2,0.5)
id:phyllocol  value:rgb(0.7,0.4,1)
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align:center  textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5)
text:Siderikian  from:-3500  till:0 color:sidericol
text:Theiikian from:-4000 till:-3500  color:theiicol
text:Phyllocian from:start till:-4000  color:phyllocol
</timeline>
==See also==
* [[Geology of Mars]]
* [[Mars carbonate catastrophe]]
==Notes==
{{noteslist}}
==References==
{{reflist|30em}}
;Bibliography
* Carr, Michael, H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, {{ISBN|978-0-521-87201-0}}.
==Further reading==
* Boyce, Joseph, M. (2008). ''The Smithsonian Book of Mars;'' Konecky & Konecky: Old Saybrook, CT, {{ISBN|978-1-58834-074-0}}
* Hartmann, William, K. (2003). ''A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet;'' Workman: New York, {{ISBN|0-7611-2606-6}}.
* Morton, Oliver (2003). ''Mapping Mars: Science, Imagination, and the Birth of a World;'' Picador: New York, {{ISBN|0-312-42261-X}}.
{{Mars}}
{{Geography of Mars|geology}}
{{Portal bar|Solar System}}
[[Category:Geologic time scale of Mars]]
[[Category:Noachis quadrangle]]
[[Category:Geological units]]