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Fig. 8.3 Layers with carbonate content inside McLaughlin Crater on Mars. This view of layered
rocks on the floor of McLaughlin Crater shows sedimentary rocks that contain spectroscopic
evidence for minerals formed through interaction with water. The High Resolution Imaging
Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded the
image. A combination of clues suggests this 2.2-km-deep (1.4-mile-deep) crater once held a lake
fed by groundwater. Part of the evidence is the identification of clay and carbonate minerals within
layers visible near the center of this image. The mineral identifications come from the Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM), also on the Mars Reconnaissance
Orbiter. The scene covers an area about 550 m (one-third of a mile) across, at 337.6 ı east longitude,
21.9 ı north latitude. It indicates the location of layers bearing clay and carbonate minerals and
includes a scale bar of 100 m (328 ft). North is up ( http://www.nasa.gov/mission_pages/MRO/
multimedia/pia16710.html and http://www.nature.com/ngeo/journal/v6/n2/abs/ngeo1706.html -
NASA/JPL-Caltech/University of Arizona, 2012)
of the fossils. It was found that most of the organic matter in the meteorite was of
terrestrial origin. More about Martian meteorites will be treated with detail later in
this chapter.
8.3.3
Geomorphic Evidence
8.3.3.1
Lakes and River Valleys
The 1971 Mariner 9 spacecraft caused a revolution in our ideas about water on
Mars. Huge river valleys were found in many areas. Images showed that floods
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