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Sedimentary rock on Mars suggests large, ancient lake beds


                   By Richard Stenger

                   (CNN) -- Scientists looking at satellite
                   images of Mars have detected evidence
                   of sedimentary rock dating back
                   billions of years, suggesting that the
                   planet once teemed with large lakes.

                   If Mars harbored life in its early history, fossils might be found within such
                   sedimentary rock layers, according to planetary researchers.

                   NASA plans to send numerous rovers and satellites to Mars this decade to
                   search for signs of water or life. But the agency might have to wait for the next
                   generation of spacecraft before it can search the newly discovered sites.

                   The outcrops, some several kilometers thick, are
                   situated inside steep gullies, inside craters and
                   between craters, locations too dangerous for the
                   current slate of NASA probes to visit.

                   "Such locations are inaccessible to presently
                   conceived lander/rover missions, which are
                   dictated by engineering constraints rather than
                   science objectives," said Michael Malin and
                   Kenneth Edgett in a recent correspondence to the
                   American Geophysical Union.

                   'Hundreds of layers'

                   Malin and Edgett, authors of the new report, are
                   conducting an extensive study of high-resolution images taken by the Mars
                   Global Surveyor, which has orbited the red planet since 1997.

                   The two created a scientific stir in June when they announced the discovery of
                   visual evidence of recent water flow near the surface of Mars.

                   According to their study, to be published in the December 8 issue of Science,
                   Mars has numerous layered geologic outcrops that date back at least 3.5 billion
                   years, early in the planet's geologist history.

                   The prevalence of such outcrops in basins and craters suggest that water
                   carried the sediments into the depressions and formed lakes inside them, they

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

                   Malin and Edgett acknowledge that many questions remain. Mars has no traces
                   of gullies or streams through which water might have transported the
                   sediments. They speculate that erosion might have wiped out signs of such

                   Malin likened the geologic history of Mars to a jigsaw puzzle.

                   "In the center of the puzzle, we have these layered rocks, which are good
                   evidence of an extremely dynamic environment," Malin said.

                   "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

                   Other explanations

                   They also allow that other processes might be responsible for the sedimentary
                   layering. Periods of high atmospheric pressure, caused by fluctuations in
                   carbon dioxide levels, could have increased the ability of the air to carry surface

                   Mars scientists James Head III of Brown University greeted the new report
                   with excitement.

                   "I think they've made a compelling case that sedimentation took place," he said.

                   "One of the interesting things about this new (Mars Global Surveyor) data -- it's
                   kind of like looking at Mars under the microscope. You can see things you
                   couldn't possibly see before."

                   "Seeing layers is really important. It means we can get to a new level of
                   discussion about the origins of these things," said Brown, who last December
                   said Surveyor images landforms that resembled ancient coastlines.

                   "If conditions might have been appropriate for life, these are important
                   candidate sites to look for fossils," Head added. On Earth, sedimentary rock
                   layers are prime locations to find the fossil remains of ancient life forms.

                   Other red planet researchers were not so enthusiastic.

                   "Maybe there are more details about what has been shown before, but there is
                   nothing strikingly new to the Mars science community," said Kenneth Tanaka
                   of the U.S. Geologic Survey.

                   "The question is, what is the source of that layering. There are different ways
                   you can get sedimentary layers. What they seem to prefer is to say that it was
                   done by water. But they also say it might be dry sources," said Tanaka, who
                   has proposed that carbon dioxide, not water, could have shaped geologic
                   features on Mars.

                   "Was it water, carbonated water or something even more exotic?" he said.

November  2000 
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