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Hesperian

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This article is about the Mars geologic system and time period. For other senses, seeHesperia.
Hesperian
3700 – 3000Ma(upper bound uncertain – between about 3200 and 2000 million years ago)
MOLAcolorized relief map ofHesperia Planum,thetype areafor the Hesperian System. Note that Hesperia Planum has fewer large impact craters than the surroundingNoachianterrain, indicating a younger age. Colors indicate elevation, with red highest, yellow intermediate, and green/blue lowest.
Chronology
SubdivisionsEarly Heperian
Late Hesperian
Usage information
Celestial bodyMars
Time scale(s) usedMartian Geologic Timescale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
Type sectionHesperia Planum

TheHesperianis ageologic systemandtime periodon the planetMarscharacterized by widespreadvolcanic activityand catastrophic flooding that carved immenseoutflow channelsacross the surface. The Hesperian is an intermediate and transitional period of Martian history. During the Hesperian, Mars changed from the wetter and perhaps warmer world of theNoachianto the dry, cold, and dusty planet seen today.[1]Theabsolute ageof the Hesperian Period is uncertain. The beginning of the period followed the end of theLate Heavy Bombardment[2]and probably corresponds to the start of the lunarLate Imbrianperiod,[3][4]around 3700 million years ago (Mya). The end of the Hesperian Period is much more uncertain and could range anywhere from 3200 to 2000 Mya,[5]with 3000 Mya being frequently cited. The Hesperian Period is roughly coincident with the Earth's earlyArcheanEon.[2]

With the decline of heavy impacts at the end of the Noachian,volcanismbecame the primary geologic process on Mars, producing vast plains offlood basaltsand broad volcanic constructs (highland paterae).[6]By Hesperian times, all of the largeshield volcanoeson Mars, includingOlympus Mons,had begun to form.[7]Volcanic outgassing released large amounts ofsulfur dioxide(SO2) andhydrogen sulfide(H2S) into the atmosphere, causing a transition in the style ofweatheringfrom dominantlyphyllosilicate(clay) tosulfatemineralogy.[8]Liquid water became more localized in extent and turned more acidic as it interacted with SO2and H2S to formsulfuric acid.[9][10]

By the beginning of the Late Hesperian the atmosphere had probably thinned to its present density.[10]As the planet cooled,groundwaterstored in the upper crust (megaregolith) began to freeze, forming a thickcryosphereoverlying a deeper zone of liquid water.[11]Subsequent volcanic or tectonic activity occasionally fractured the cryosphere, releasing enormous quantities of deepgroundwaterto the surface and carving hugeoutflow channels.Much of this water flowed into the northern hemisphere where it probably pooled to form large transient lakes or an ice covered ocean.

Description and name origin[edit]

TheHesperianSystem and Period is named afterHesperia Planum,a moderately cratered highland region northeast of theHellasbasin. Thetype areaof the Hesperian System is in theMare Tyrrhenum quadrangle(MC-22) around20°S245°W/ 20°S 245°W/-20; -245.The region consists of rolling,wind-streakedplains with abundantwrinkle ridgesresembling those on thelunar maria.These "ridged plains" are interpreted to be basaltic lava flows (flood basalts) that erupted from fissures.[12]The number-density of large impact craters is moderate, with about 125–200 craters greater than 5 km in diameter per million km2.[3][13]Hesperian-aged ridged plains cover roughly 30% of the Martian surface;[2]they are most prominent in Hesperia Planum,Syrtis Major Planum,Lunae Planum, Malea Planum, and the Syria-Solis-Sinai Plana in southernTharsis.[14][15]

Pre-NoachianNoachianAmazonian (Mars)
Martian Time Periods (Millions of Years Ago)

Hesperian chronology and stratigraphy[edit]

Schematic cross section of image at left. Surface units are interpreted as a sequence of layers (strata), with the youngest at top and oldest at bottom in accordance with thelaw of superposition.
HiRISEimage illustratingsuperpositioning,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 at right. The ejecta of the crater at center overlies both units, indicating that the crater is the youngest feature in the image. (See cross section, above right.)

Martian time periods are based ongeologic mappingof surface units fromspacecraft images.[12][16]A surface unit is a terrain with a distinct texture, color,albedo,spectralproperty, or set of landforms that distinguish it from other surface units and is large enough to be shown on a map.[17]Mappers use astratigraphicapproach pioneered in the early 1960s for photogeologic studies of theMoon.[18]Although based on surface characteristics, a surface unit is not the surface itself or group oflandforms.It is aninferredgeologic unit(e.g.,formation) representing a sheetlike, wedgelike, or tabular body of rock that underlies the surface.[19][20]A surface unit may be a crater ejecta deposit, lava flow, or any surface that can be represented in three dimensions as a discretestratumbound above or below by adjacent units (illustrated right). Using principles such assuperpositioning(illustrated left),cross-cutting relationships,and the relationship ofimpact crater densityto age, geologists can place the units into arelative agesequence from oldest to youngest. Units of similar age are grouped globally into larger, time-stratigraphic (chronostratigraphic) units, calledsystems.For Mars, four systems are defined: the Pre-Noachian,Noachian,Hesperian, and Amazonian. Geologic units lying below (older than) the Noachian are informally designated Pre-Noachian.[21]The geologic time (geochronologic) equivalent of the Hesperian System is the Hesperian Period. Rock or surface units of the Hesperian System were formed or deposited during the Hesperian Period.

System vs. period[edit]

eh
Segments of rock (strata) inchronostratigraphy Periods of time ingeochronology Notes (Mars)
Eonothem Eon not used for Mars
Erathem Era not used for Mars
System Period 3 total; 108to 109years in length
Series Epoch 8 total; 107to 108years in length
Stage Age not used for Mars
Chronozone Chron smaller than an age/stage; not used by the ICS timescale

Systemandperiodare not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system is an idealized stratigraphiccolumnbased on the physical rock record of atype area(type section) correlated with rocks sections from many different locations planetwide.[23]A system is bound above and below bystratawith distinctly different characteristics (on Earth, usuallyindex fossils) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (SeeCretaceous–Paleogene boundaryas example.)

At any location, rock sections in a given system are apt to contain gaps (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 theCretaceousSystem 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 thestrataof a system were deposited, including any unknown amounts of time present in gaps.[23]Periods are measured in years, determined byradioactive dating.On Mars, radiometric ages are not available except fromMartian meteoriteswhoseprovenanceand stratigraphic context are unknown. Instead,absolute ageson Mars are determined by impact crater density, which is heavily dependent uponmodelsof crater formation over time.[24]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.[4][21]

Boundaries and subdivisions[edit]

Geologic contact of Noachian and Hesperian Systems. Hesperian ridged plains (Hr) embay and overlie older Noachian cratered plateau materials (Npl). The ridged plains partially bury many of the old Noachian-aged craters. Image isTHEMISIR mosaic, based on similarVikingphoto shown in Tanakaet al.(1992), Fig. 1a, p. 352.
Approximate geologic contact of Upper Hesperian lava apron fromAlba Mons(Hal) with Lower Amazonian Vastitas Borealis Formation (Avb). Image isMOLAtopographic map adapted from Ivanov and Head (2006), Figs. 1, 3, and 8.[25]

The lower boundary of the Hesperian System is defined as the base of the ridged plains, which are typified by Hesperia Planum and cover about a third of the planet's surface.[3]In eastern Hesperia Planum, the ridged plains overlie early to mid Noachian aged cratered plateau materials (pictured left).[15]The Hesperian's upper boundary is more complex and has been redefined several times based on increasingly detailed geologic mapping.[3][12][26]Currently, the stratigraphic boundary of the Hesperian with the younger Amazonian System is defined as the base of the Vastitas Borealis Formation[27](pictured right). TheVastitas Borealisis a vast, low-lying plain that covers much of the northern hemisphere of Mars. It is generally interpreted to consist of reworked sediments originating from the Late Hesperian outflow channels and may be the remnant of an ocean that covered the northern lowland basins. Another interpretation of the Vastitas Borealis Formation is that it consists of lava flows.[28]

The Hesperian System is subdivided into two chronostratigraphicseries:Lower Hesperian and Upper Hesperian. The series are based onreferentsor locations on the planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, Hesperia Planum is the referent location for the Lower Hesperian Series.[3][29]The corresponding geologic time (geochronological) units of the two Hesperian series are the Early Hesperian and Late HesperianEpochs.An epoch is a subdivision of a period; the two terms are not synonymous in formal stratigraphy. The age of the Early Hepserian/Late Hesperian boundary is uncertain, ranging from 3600 to 3200 million years ago based on crater counts.[5]The average of the range is shown in the timeline below.

Hesperian Epochs (Millions of Years Ago)[5]

Stratigraphic terms are typically confusing to geologists and non-geologists alike. One way to sort through the difficulty is by the following example: One could easily go toCincinnati, Ohioand visit a rockoutcropin the UpperOrdovicianSeriesof the OrdovicianSystem.You could even collect a fossiltrilobitethere. However, you could not visit the Late OrdovicianEpochin the OrdovicianPeriodand collect an actual trilobite.

The Earth-based scheme of rigid 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.[30](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 chronology.[31]

Mars during the Hesperian Period[edit]

Viking orbiterview of Hesperian-aged surface inTerra Meridiani.The small impact craters date back to the Hesperian Period and appear crisp despite their great age. This image indicates that erosion on Mars has been very slow since the end of theNoachian.Image is 17 km across and based on Carr, 1996, p. 134, Fig. 6-8.[32]

The Hesperian was a time of declining rates of impact cratering, intense and widespread volcanic activity, and catastrophic flooding. Many of the majortectonicfeatures on Mars formed at this time. The weight of the immenseTharsis Bulgestressed the crust to produce a vast network of extensional fractures (fossae) and compressive deformational features (wrinkle ridges) throughout the western hemisphere. The huge equatorial canyon system ofValles Marinerisformed during the Hesperian as a result of these stresses. Sulfuric-acid weathering at the surface produced an abundance of sulfate minerals that precipitated inevaporitic environments,which became widespread as the planet grew increasingly arid. The Hesperian Period was also a time when the earliest evidence of glacial activity and ice-related processes appears in the Martian geologic record.

Impact cratering[edit]

As originally conceived, the Hesperian System referred to the oldest surfaces on Mars that postdate the end ofheavy bombardment.[33]The Hesperian was thus a time period of rapidly declining impact cratering rates. However, the timing and rate of the decline are uncertain. The lunar cratering record suggests that the rate of impacts in the innerSolar Systemduring theNoachian(4000 million years ago) was 500 times higher than today.[34]Planetary scientists still debate whether these high rates represent the tail end ofplanetary accretionor a late cataclysmic pulse that followed a more quiescent period of impact activity. Nevertheless, at the beginning of the Hesperian, the impact rate had probably declined to about 80 times greater than present rates,[4]and by the end of the Hesperian, some 700 million years later, the rate began to resemble that seen today.[35]

Notes and references[edit]

  1. ^Hartmann, 2003, pp. 33–34.
  2. ^abcCarr, M. H.; Head, J. W. (2010)."Geologic history of Mars".Earth and Planetary Science Letters.294(3–4): 185–203.Bibcode:2010E&PSL.294..185C.doi:10.1016/j.epsl.2009.06.042.
  3. ^abcdeTanaka, K. L. (1986)."The stratigraphy of Mars".Journal of Geophysical Research.91(B13): E139–E158.Bibcode:1986LPSC...17..139T.doi:10.1029/JB091iB13p0E139.
  4. ^abcHartmann, W. K.; Neukum, G. (2001). "Cratering Chronology and the Evolution of Mars".Space Science Reviews.96:165–194.Bibcode:2001SSRv...96..165H.doi:10.1023/A:1011945222010.S2CID7216371.
  5. ^abcHartmann, W. K. (2005). "Martian cratering 8: Isochron refinement and the chronology of Mars".Icarus.174(2): 294–320.Bibcode:2005Icar..174..294H.doi:10.1016/j.icarus.2004.11.023.
  6. ^Greeley, R.; Spudis, P. D. (1981). "Volcanism on Mars".Reviews of Geophysics.19(1): 13–41.Bibcode:1981RvGSP..19...13G.doi:10.1029/RG019i001p00013.
  7. ^Werner, S. C.(2009). "The global martian volcanic evolutionary history".Icarus.201(1): 44–68.Bibcode:2009Icar..201...44W.doi:10.1016/j.icarus.2008.12.019.
  8. ^Bibring, J.-P.; Langevin, Y.; Mustard, J. F.; Poulet, F.; Arvidson, R.; Gendrin, A.; Gondet, B.; Mangold, N.; Pinet, P.; Forget, F.; Berthe, M.; Bibring, J.-P.; Gendrin, A.; Gomez, C.; Gondet, B.; Jouglet, D.; Poulet, F.; Soufflot, A.; Vincendon, M.; Combes, M.; Drossart, P.;Encrenaz, T.;Fouchet, T.; Merchiorri, R.; Belluci, G.; Altieri, F.; Formisano, V.; Capaccioni, F.; Cerroni, P.; Coradini, A.; Fonti, S.; Korablev, O.; Kottsov, V.; Ignatiev, N.; Moroz, V.; Titov, D.; Zasova, L.; Loiseau, D.; Mangold, N.; Pinet, P.; Doute, S.; Schmitt, B.; Sotin, C.; Hauber, E.; Hoffmann, H.; Jaumann, R.; Keller, U.; Arvidson, R.; Mustard, J. F.; Duxbury, T.; Forget, F.; Neukum, G. (2006). "Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data".Science.312(5772): 400–404.Bibcode:2006Sci...312..400B.doi:10.1126/science.1122659.PMID16627738.
  9. ^Head, J.W.; Wilson, L. (2011). The Noachian-Hesperian Transition on Mars: Geological Evidence for a Punctuated Phase of Global Volcanism as a Key Driver in Climate and Atmospheric Evolution. 42nd Lunar and Planetary Science Conference (2011), Abstract #1214.http:// lpi.usra.edu/meetings/lpsc2011/pdf/1214.pdf.
  10. ^abBarlow, N. G. (2010). "What we know about Mars from its impact craters".Geological Society of America Bulletin.122(5–6): 644–657.Bibcode:2010GSAB..122..644B.doi:10.1130/B30182.1.
  11. ^Clifford, S. M. (1993). "A model for the hydrologic and climatic behavior of water on Mars".Journal of Geophysical Research.98(E6): 10973–11016.Bibcode:1993JGR....9810973C.doi:10.1029/93JE00225.
  12. ^abcScott, D.H.; Carr, M.H. (1978). Geologic Map of Mars. U.S. Geological Survey Miscellaneous Investigations Series Map I-1083.
  13. ^Strom, R.G.; Croft, S.K.; Barlow, N.G. (1992) The Martian Impact Cratering Record inMars,H.H. Kiefferet al.,Eds.; University of Arizona Press: Tucson, AZ, pp. 383–423.
  14. ^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.
  15. ^abGreeley, 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.
  16. ^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:// lpi.usra.edu/meetings/lpsc1980/pdf/1249.pdf.
  17. ^Greeley, R. (1994)Planetary Landscapes,2nd ed.; Chapman & Hall: New York, p. 8 and Fig. 1.6.
  18. ^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.
  19. ^Wilhelms, D.E. (1990). Geologic Mapping inPlanetary Mapping,R. Greeley, R.M. Batson, Eds.; Cambridge University Press: Cambridge UK, p. 214.
  20. ^Tanaka, K.L.; Scott, D.H.; Greeley, R. (1992). Global Stratigraphy inMars,H.H. Kiefferet al.,Eds.; University of Arizona Press: Tucson, AZ, pp. 345–382.
  21. ^abNimmo, F.; Tanaka, K. (2005). "Early Crustal Evolution of Mars".Annual Review of Earth and Planetary Sciences.33(1): 133–161.Bibcode:2005AREPS..33..133N.doi:10.1146/annurev.earth.33.092203.122637.
  22. ^International Commission on Stratigraphy."International Stratigraphic Chart"(PDF).Retrieved2009-09-25.
  23. ^abEicher, D.L.; McAlester, A.L. (1980).History of the Earth;Prentice-Hall: Englewood Cliffs, NJ, pp 143–146,ISBN0-13-390047-9.
  24. ^Masson, P.; Carr, M.H.; Costard, F.; Greeley, R.; Hauber, E.; Jaumann, R. (2001). "Geomorphologic Evidence for Liquid Water".Space Science Reviews.Space Sciences Series of ISSI.96:333–364.doi:10.1007/978-94-017-1035-0_12.ISBN978-90-481-5725-9.
  25. ^Ivanov, M. A.; Head, J. W. (2006)."Alba Patera, Mars: Topography, structure, and evolution of a unique late Hesperian–early Amazonian shield volcano".Journal of Geophysical Research.111(E9): E09003.Bibcode:2006JGRE..111.9003I.doi:10.1029/2005JE002469.
  26. ^Tanaka, K.L.; Skinner, J.A.; Hare, T.M. (2005). Geologic Map of the Northern Plains of Mars. Scientific Investigations Map 2888, Pamphlet; U.S. Geological Survey.
  27. ^The Vastitas Borealis Formation is used here to include the Lower Amazonian Scandia, Vastitas Borealis interior, and Vastitas Borealis marginal units of Tanakaet al.(2005).
  28. ^Catling, D.C.; Leovy, C.B.; Wood, S.E.; Day, M.D. (2011). A Lava Sea in the Northern Plains of Mars: Circumpolar Hesperian Oceans Reconsidered. 42nd Lunar and Planetary Science Conference, Abstract #2529.http:// lpi.usra.edu/meetings/lpsc2011/pdf/2529.pdf.
  29. ^Masson, P. L. (1991). "The Martian stratigraphy — Short review and perspectives".Space Science Reviews.56(1–2): 9–12.Bibcode:1991SSRv...56....9M.doi:10.1007/BF00178385.S2CID121719547.
  30. ^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:// lpi.usra.edu/meetings/lpsc2001/pdf/1695.pdf.
  31. ^Carr, 2006, p. 41.
  32. ^Carr, M.H. (1996).Water on Mars;Oxford University Press: Oxford, UK, 229 pp,ISBN0-19-509938-9.
  33. ^Carr, 2006, p. 15.
  34. ^Carr, 2006, p. 23.
  35. ^Fassett, C. I.; Head, J. W. (2011). "Sequence and timing of conditions on early Mars".Icarus.211(2): 1204–1214.Bibcode:2011Icar..211.1204F.doi:10.1016/j.icarus.2010.11.014.

Bibliography and recommended reading[edit]

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