Noachian

This article is about the Martian geologic system and period. For the Biblical patriarch of whom "Noachian" is the derived adjective, see Noah.
Noachian
4100 – 3700 Ma
MOLA colorized relief map of Noachis Terra, the 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 impact basin.
Chronology
SubdivisionsEarly Noachian

Middle Noachian

Late Noachian
Usage information
Celestial bodyMars
Time scale(s) usedMartian Geologic Timescale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
Type sectionNoachis Terra

The Noachian is a geologic system and early time period on the planet Mars characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water.[1] The absolute age of the Noachian period is uncertain but probably corresponds to the lunar Pre-Nectarian to Early Imbrian periods[2] of 4100 to 3700 million years ago, during the interval known as the Late Heavy Bombardment.[3] 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.[4]

Noachian-aged terrains on Mars are prime spacecraft landing sites to search for fossil evidence of life.[5][6][7] 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.[8] Large lakes and rivers were present in the southern hemisphere,[9][10] and an ocean may have covered the low-lying northern plains.[11][12] 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.[3] Weathering of surface rocks produced a diversity of clay minerals (phyllosilicates) that formed under chemical conditions conducive to microbial life.[13][14]

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.[15] 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.[16] 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.[17][18] 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.[19] Other researchers argue for a semiarid early Mars with at least transient periods of rainfall warmed by a carbon dioxide-hydrogen atmosphere.[20] 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.[21] 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.[22][23][24]

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  9. ^ Malin, M.C.; Edgett, K.S. (2003). "Evidence for Persistent Flow and Aqueous Sedimentation on Early Mars". Science. 302 (5652): 1931–1934. Bibcode:2003Sci...302.1931M. doi:10.1126/science.1090544. PMID 14615547. S2CID 39401117.
  10. ^ Irwin, R.P.; et al. (2002). "A Large Paleolake Basin at the Head of Ma'adim Vallis, Mars". Science. 296 (5576): 2209–12. Bibcode:2002Sci...296.2209R. doi:10.1126/science.1071143. PMID 12077414. S2CID 23390665.
  11. ^ Clifford, S.M.; Parker, T.J. (2001). "The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains". Icarus. 154 (1): 40–79. Bibcode:2001Icar..154...40C. doi:10.1006/icar.2001.6671.
  12. ^ Di Achille, G.; Hynek, B.M. (2010). "Ancient Ocean on Mars Supported by Global Distribution of Deltas and Valleys". Nature Geoscience. 3 (7): 459–463. Bibcode:2010NatGe...3..459D. doi:10.1038/NGEO891.
  13. ^ Bibring, J.-P.; et al. (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. PMID 16627738.
  14. ^ Bishop, J.L.; et al. (2008). "Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars" (PDF). Science (Submitted manuscript). 321 (5890): 830–833. Bibcode:2008Sci...321..830B. doi:10.1126/science.1159699. PMC 7007808. PMID 18687963.
  15. ^ 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.
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  19. ^ 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
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