Click on the image for a larger version
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Rock Varnish |
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Click on the image for a larger version
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Rock Varnish |
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Rock Varnish, Capitol Reef National Park, Utah |
Credit & Copyright: Dr. Bruce G.
Marcot
| Explanation: Just
a few uninteresting stains on a canyon wall, you say? Look closer.
This is rock
varnish, also called desert
varnish. It is a combination of particles of clay, iron and
manganese oxides, hydroxides, silica, and calcium carbonate ... glued to the
rock surface by living bacteria or lichens, which use the varnish as a
protective covering. Rock
varnish forms in many environments, but is most obvious in deserts, such
as in this photo taken in Capitol
Reef National Park in southern Utah. (View
a slide sequence of rock varnish in southwest U.S.)
The bacteria in rock varnish might tell us something about how primitive life forms may occur on other planets, and where we might look for them ... such as on canyon walls and rocks and even caves of Mars. Rock varnish forms over decades to centuries, and may last for millennia if undisturbed. Some ancient cultures created pictographs by chipping away the varnish into recognizable images.
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Next week's picture: Spotted Hyena: Extreme Scavenger
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