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HOT!!! Mars Home to Ancient Lakes

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  • Jeroen Kumeling
    Mars Home to Ancient Lakes By Robert Roy Britt Senior Science Writer posted: 10:35 am ET 04 December 2000 Special Report: Continuing Coverage of the Mars Water
    Message 1 of 1 , Dec 4, 2000
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      Mars Home to Ancient Lakes

      By Robert Roy Britt
      Senior Science Writer
      posted: 10:35 am ET
      04 December 2000
      Special Report: Continuing Coverage of the Mars Water Discovery



      Eight examples of very similar outcrops of light-toned, layered,
      cliff-forming material exposed in locations separated by hundreds to
      thousands of kilometers


      Left image shows relative brightness of light, intermediate, and dark-toned
      outcrops. Right image shows thin-bedded outcrops compared to thick-bedded
      outcrops.



      Layered geologic outcrops on Mars may be composed of sedimentary rock that
      dates from the earliest span of martian history, between 4.3 and 3.5 billion
      years ago, according to an interpretation of newly released images from the
      Mars Orbiter Camera.

      Images of these sedimentary rock exposures suggest that parts of ancient
      Mars may have resembled a land of lakes, and that the geology of early Mars
      was much more dynamic than previously suspected, say researchers affiliated
      with the Mars Orbiter project.

      If life existed on Mars during this time period, the researchers believe
      that the fossil remnants of that past life may be sandwiched within the
      sedimentary rock layers, just as they are on Earth.

      The martian outcrops, in some cases a few kilometers thick, appear to be
      made of fine-grained materials deposited in horizontal layers, the hallmark
      of sedimentary rock. These outcrops are found inside craters, between
      craters, and within chasms, said Michael Malin and Kenneth Edgett of Malin
      Space Science Systems in San Diego, California.

      The researchers identified three main outcrop types from the MOC images:
      layered units, massive units, and thin mesa units.

      Layered units, as their name suggests, consist of relatively thin rock
      beds--some only a few meters thick--stacked on top of one another in
      distinct groups. Massive units appear as on bulky rock layer with no clearly
      defined horizontal bedding. In a few cases, these types appear together,
      with the massive unit always perched on top of the bedded unit like a thick,
      indistinct coat of frosting on a layer cake.

      Thin mesa units, with surfaces ranging from smooth to pitted to ridged and
      grooved, are almost always found on top of eroded massive or layered
      sedimentary rock.

      While sediments can be deposited in a variety of ways--including wind,
      water, volcanic activity, and even cosmic impact--the prevalence of the
      martian sedimentary outcrops within basin-like features suggests that they
      were deposited by water, perhaps in lakes that formed within the craters and
      chasms, said Malin and Edgett.

      Under this scenario, sediments may have been transported into the lakes in
      regular, swift pulses, building up thin layer units. Massive units may have
      been deposited when the lake became stagnant or deep enough to cause
      sediments to sift down through the water over longer intervals.

      "Some of the MOC images of these outcrops show hundreds and hundreds of
      identically thick layers, which is almost impossible to have without water,"
      said Malin.


      Eight examples of very similar outcrops of light-toned, layered,
      cliff-forming material exposed in locations separated by hundreds to
      thousands of kilometers


      Left image shows relative brightness of light, intermediate, and dark-toned
      outcrops. Right image shows thin-bedded outcrops compared to thick-bedded
      outcrops.


      A paper on the images will appear in this Friday's issue of the journal
      Science. The findings were to be reported at a NASA news conference
      Thursday, after an embargo on the information lifted. That embargo was
      lifted today, after other news organizations published accounts of the
      study.

      The sedimentary units show no telltale signs of wind deposition, and the
      researchers concluded that explosive volcanic eruptions and impact cratering
      probably could not have produced enough sediment to create the large-scale
      and geographically widespread outcrops seen on the martian surface.

      Although Malin and Edgett favor water as the sedimentary suspect, they also
      offer an alternative model that involves changes in atmospheric pressure on
      early Mars. They suggest that periods of relatively high atmospheric
      pressure -- caused by fluctuations in the amount of solid carbon dioxide on
      the planet's surface--could have increased the atmosphere's ability to carry
      dust produced by heavy cratering.

      To confuse matters, the researchers don't know where the original sediments
      came from, or how they were transported to their final resting places, since
      there are no traces of gullies or streams or other channels associated with
      the outcrops. They think that erosion may have wiped out both the source of
      the sediments and their travel routes.

      In some cases, sedimentary rock has eroded out of the crater in which it
      formed, also vanishing without a geologic clue.

      To Malin, the history of martian geology looks like a jigsaw puzzle.

      "In the center of the puzzle, we have these layered rocks, which are good
      evidence of an extremely dynamic environment. On either side of this
      well-developed puzzle piece, we have mysteries." In any case, Mars'
      sedimentary rocks suggest a very active early history for the planet.

      "This makes Mars more complicated and more exciting. This record is going to
      tell us a lot about what early Mars was like, and maybe the early Earth as
      well, since we don't have a lot of rocks on our own planet from this time
      period," said Edgett.
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