Hesperian (Mars)

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The Hesperian describes a geological system and a period of time on Mars, in which the brisk volcanic activity and immense flooding shaped the landscape of the planet. The Hesperian denotes an intermediate and transition period in the history of the planet. During this transition period, the more humid and probably warmer surface of the planet (of the Nochian age) turned into the dry and cold dusty desert we know today. However, the exact age and duration of the Hesperian Age is not known precisely. The beginning of this time period is marked by the end of the Great Bombardment and correlates with the beginning of the Late Imbrian Period of the Moon about 3.7 billion years ago. The end of the Hesperian era is dated between 3.2 and 2.0 billion years before the Common Era. An age of 3 billion years is often assumed, which roughly coincides with the Earth's early Archean .

After the heavy meteorite impacts stopped at the end of the Nochian, only volcanic activity was responsible for the primary geological processes. They produced wide plains full of flood basalts and formed volcanic structures. In the Hesperian, all large shield volcanoes such as Olympus Mons formed . Volcanic gases released a large amount of sulfur dioxide (SO 2 ) and hydrogen sulfide (H 2 S) into the atmosphere, which led to a change in the weathering process from silicate to sulfate minerals. The liquid water concentrated at certain points, and was passed through a reaction with SO 2 and H 2 S to sulfuric acid H 2 SO 4 .

At the beginning of the late Hesperian, the atmosphere had already thinned to its current level. As the planet continued to cool, the water in the Earth's upper crust froze to ice, creating a cryosphere for lower groundwater . This cryosphere was later ruptured by volcanic and seismic activity, and as a result, huge amounts of groundwater surged to the surface and formed huge channels. Most of the water flowed into the northern hemisphere, where it temporarily formed large lakes or an ice-covered ocean.

Description and origin of name

The Hesperian period was named after the Marsh Highlands Hesperia Planum . This is a highland area that is criss-crossed by a few craters and is located northeast of the Hellas impact basin. The area can be found on the map "Mare Tyrrhenum quadrangle" (MC-22) at the coordinates 20 ° S 245 ° W. The region is dominated by wide fluted plains called the dorsum, which are similar to the surface of the moon (Lunar Mare). Eruptions, which emerged through numerous cracks in the ground, formed step -shaped structures due to the deposition of flood basalts , which is responsible for this corrugation of the levels. The number of craters in this area is moderate and amounts to 125-200 pieces per 1 million km², which are larger than 5 km in diameter. Plains formed in the Hesperian cover roughly 30% of the planet. These geological systems occur most frequently in the Hesperia Planum, Syrtis Major Planum, Lunae Planum, Malea Planum, and Syria-Solis-Sinai Planum (southern Tharsis ).

Noachian Noachian Amazonian (Mars)
Mars age (x million years ago)

Stratigraphy and Hesperian Chronology

The time periods of Mars are based on geological recordings ( geological map ), which were made by space probes ( remote sensing ). A geological map is a terrain that differs from other areas in terms of texture, color, albedo, spectral properties or certain landscape formations and is large enough to be displayed on a map. However, a geological map describes more than just the visible surface in a geological sense. It can be about crater ejection, deposits, lava flows or any kind of surface texture that can be represented in three-dimensional space. Using geological methods such as overlay, cross-sectional relationship and the ratio of the impact craters (density, age), the geologists can classify the surface units from the oldest to the youngest. Units with a similar age are combined into so-called chronostratigraphic units and referred to as a system. Three systems have been defined for Mars: Nochian, Hesperian, Amazonian. Geological structures that lie below the Nochian layers are called Pre-Nochian. The geological age, which is equivalent to the Hesperian geological system, is called the Hesperian period. All geological formations of the Hesperian were created during this time period.

Difference Between System and Period

In the hierarchy of ranks of the chronostratigraphic units, a system is the middle of a total of five units. In geochronology , this period corresponds to the unit period. The terms system and period are often - but not entirely correctly - used as synonyms in the literature. The boundaries of the chronostratigraphic unit system are limited by isochronous (simultaneous) stratigraphic areas that are defined by biostratigraphic markers or other events. The systems are relatively defined by the interfaces between two successive systems and by their sequence in time; H. the absolute age of the interfaces and the absolute time span of a system are not included in this definition, since the absolute ages of the interfaces can still change due to other or newer methods of age determination such as radiometric dating. Since radiometric dating is not possible on Mars, the classification is based on the density and distribution of impact craters, which in turn is very model-dependent. This results in a very imprecise division of the time periods. Especially the beginning and the end of the Hesperian and the Amazonian can vary by a factor of 2 to 3.

Boundaries and subdivisions

The lower limit of the Hesperian system is spanned by the lower part of the fluted plains, which are a typical structure of the Hesperian planum and cover about a third of the planet. In the east of the Hesperia Planum , the corrugated plains cover the crater material from the earlier and middle Nochian. The upper limits are defined somewhat more complex and have been redefined over and over again as more and more accurate geological data became available. Currently, the Hesperian stratigraphic boundary is defined as the base of the Vasitas Borealis Formation. The Vasitas Borealis is a huge plain that covers a large part of the northern hemisphere. It is believed that the sediment deposits in this area were formed by large outflow openings, but they could also be the remains of an ocean that once covered the northern lowlands. Another interpretation of the formation of the vastitas borealis says that it emerged from lava flows.

The Hesperian system is divided into two chronostratigraphic series: lower / early Hesperian and higher / later Hesperian. The division is based on certain reference points and locations on the planet at which an exact geological sequence over time can be recognized. For example, the Hesperia Planum is the reference point for the lower Hesperian. The corresponding time periods are called early Hesperian epoch and late Hesperian epoch. It should be noted that an epoch is used to subdivide a period. Here, too, the terms must not be used synonymously. The exact age of the Hesperian epochs can only be estimated from the crater distribution and is between 3600 and 3200 million years. The approximate time span can be seen in the graphic below.

Hesperian epochs (x million years ago)

Earth's stratigraphic nomenclature has been used successfully on Mars for decades, but it also contains numerous errors. A major overhaul will be needed in this area as soon as more accurate data is available. For a closer look, the radiometric dating of the Martian rock is necessary and this will only be possible in the future.

Mars during the Hesperian period

The Hesperian was an age of great floods and high volcanic activity. The meteorite impacts became increasingly rare and most of the tectonic processes of Mars took place during this time period. The great weight of the Tharsis Plateau created a large network of cracks and deformations in the western hemisphere. In this process, the great equatorial canyon Valles Marineris was created . The sulfuric acid weather produced a large amount of sulphurous minerals. As the climate got drier, large-scale evaporites formed . The Hesperian was also an age in which glacier and ice -related processes first appeared in the geological record of Mars.

The importance of the impact crater

As intended, the term Hesperian refers to the strata of Mars that date the end of the Great Bombardment . It is difficult to say at what rate the likelihood of impact decreased and over what period of time it reached today's level. By analyzing the impact craters on our moon, we can today estimate that the probability of impact in the inner solar system during the Nochian (4 billion years ago) was around 500 times higher than today. Planetary researchers do not agree to this day whether a planetary formation process came to an end with this age or whether it was a catastrophic impulse. In any case, it can be said that the probability of an impact at the beginning of the Hesperian was 80 times that of today, and at the end of the Hesperian it settled at its current level 700 million years later.

Individual evidence

  1. ↑ Hartmann, 2003, pp. 33-34.
  2. ↑ a b Carr, MH; Head, JW (2010). Geologic History of Mars. Earth planet. Sci. Lett., 294, 185-203.
  3. ↑ a b c Tanaka, KL (1986). The Stratigraphy of Mars. J. Geophys. Res., Seventeenth Lunar and Planetary Science Conference Part 1, 91 (B13), E139-E158, doi: 10.1029 / JB091iB13p0E139 . http://adsabs.harvard.edu/full/1986LPSC...17..139T .
  4. ↑ a b c Hartmann, WK; 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.
  5. ↑ a b c Hartmann, WK (2005). Martian Cratering 8: Isochron Refinement and the Chronology of Mars. Icarus, 174, 294-320.
  6. ^ Bibring, J.-P. et al. (2006). Global Mineralogical and Aqueous Mars History Derived from OMEGA / Mars Express Data. Science, 312 (400), doi: 10.1126 / science.1122659 .
  7. ^ Head, JW; 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://www.lpi.usra.edu/meetings/lpsc2011/pdf/1214.pdf .
  8. ↑ a b Barlow, NG (2010). What We Know about Mars from Its Impact Craters. Geol. Soc. At the. Bull., 122 (5/6), 644-657.
  9. ↑ Clifford, SM (1993). A Model for the Hydrologic and Climatic Behavior of Water on Mars. J. Geophys. Res., 98 (E6), 10.973-11.016.
  10. ↑ Strom, RG; Croft, SK; Barlow, NG (1992) The Martian Impact Cratering Record in Mars, HH Kieffer et al., Eds .; University of Arizona Press: Tucson, AZ, pp. 383-423.
  11. ↑ Tanaka, KL (1986). The Stratigraphy of Mars. J. Geophys. Res., Seventeenth Lunar and Planetary Science Conference Part 1, 91 (B13), E139-E158.
  12. ↑ Scott, DH; Tanaka, KL (1986). Geologic Map of the Western Equatorial Region of Mars. US Geological Survey Miscellaneous Investigations Series Map I – 1802 – A.
  13. ↑ Greeley, R .; Guest, JE (1987). Geologic Map of the Eastern Equatorial Region of Mars. US Geological Survey Miscellaneous Investigations Series Map I – 1802 – B.
  14. ↑ a b Scott, DH; Carr, MH (1978). Geologic Map of Mars. US Geological Survey Miscellaneous Investigations Series Map I-1083.
  15. ↑ McCord, TM 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 .
  16. ↑ a b Nimmo, F .; Tanaka, K. (2005). Early Crustal Evolution of Mars. Annu. Rev. Earth Planet. Sci., 33, 133-161.
  17. ↑ Masson, P .; Carr, MH; Costard, F .; Greeley, R .; Hauber, E .; Jaumann, R. (2001). Geomorphologic Evidence for Liquid Water. Space Science Reviews, 96, p. 352.
  18. ↑ Tanaka, KL; Skinner, YES; Hare, TM (2005). Geologic Map of the Northern Plains of Mars. Scientific Investigations Map 2888, pamphlet; US Geological Survey.
  19. ↑ Catling, DC; Leovy, CB; Wood, SE; Day, MD (2011). A Lava Sea in the Northern Plains of Mars: Circumpolar Hesperian Oceans Reconsidered. 42nd Lunar and Planetary Science Conference, Abstract # 2529. http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2529.pdf .
  20. ↑ Tanaka, KL (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 .
  21. ^ Carr, 2006, p. 41.
  22. ^ Carr, 2006, p. 15th
  23. ^ Carr, 2006, p. 23.
  24. ↑ Fassett, CI; Head, JW (2011). Sequence and Timing of Conditions on Early Mars. Icarus, 211, 1204-1214, doi: 10.1016 / j.icarus.2010.11.014 .

further reading

  • Boyce, Joseph, M. (2008). The Smithsonian Book of Mars; Konecky & Konecky: Old Saybrook, CT, ISBN 978-1-58834-074-0
  • Carr, Michael, H. (2006). The Surface of Mars; Cambridge University Press: Cambridge, UK, ISBN 978-0-521-87201-0 .
  • 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 .