Post by Joe Michalski, Planetary Science Institute, Tucson, Arizona, USA
On Earth, the most ancient sedimentary rock record has been largely obliterated by plate tectonics and erosion. Those that remain are from the early history of the Earth and are severely deformed and mineralogically altered. Evidence for the earliest life on Earth found within these strata is often controversial because the rocks are so severely changed from their original state.
The Mawrth Vallis region of Mars contains one of the largest exposures of phyllosilicate-bearing, sedimentary rocks on the red planet (Image 1-3). They were discovered initially using data from the Observatoire pour l’Eau, la Minéralogie, les Glaces, et l’Activité (OMEGA) instrument onboard the Mars Express spacecraft http://www.esa.int/SPECIALS/Mars_Express/SEMUC75V9ED_0.html. Since that time, further work with OMEGA and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) http://crism.jhuapl.edu/ , as well as high-resolution imaging by the High-Resolution Imaging Science Experiment (HiRISE) http://hirise.lpl.arizona.edu/ and other instruments, have shown a diverse suite of clay minerals present within a thick (>150 m) layered, complex stratigraphic section (Images 1,2).
The age of the Mawrth Vallis deposit is not known precisely – most of the stratigraphic section is extremely ancient (Mid-Late Noachian, ~3.6-4.1 Ga). The upper part of the section may have been re-worked by a later phase of aqueous processes, as suggested by apparent draping-relationships of units. This dates approximately to the timing of the Late Heavy Bombardment period in the Solar System, and may be an indication that Mars was a violent place, scarred by intense meteor impact flux during the time when the rocks formed. It also roughly coincides with the earliest evidence of life on Earth.
Future exploration of the Mawrth Vallis region from the Martian surface would reveal important new details about the mineralogy, geochemistry, texture, and organic chemistry of these deposits. This site is among the final group under consideration as a landing site for the Mars Science Laboratory (MSL) http://marsprogram.jpl.nasa.gov/msl/ mission. If MSL lands on these clay-rich, layered deposits in 2012, it could revolutionize our understanding of aqueous geological processes and organic chemical processes that took place early in the history of the Solar System.
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