such as "Introduction", "Conclusion"..etc
Dec. 19, 2008 — Over the last several years,
scientists have built a very convincing case that Mars hosted water, at
least early in its history. Recent observations from the Mars Phoenix
lander and other spacecraft show that the planet still holds vast
deposits of water as ice at its poles and in soil-covered glaciers in
What is less known is how much water occupied the red planet and
what happened to it during its geological march to the present. Mostly,
evidence has pointed to a period when clay-rich minerals were formed by
water, followed by a drier time, when salt-rich, acidic water affected
much of the planet. Assuming that happened, the thinking goes, it would
have been difficult for life, if it did exist, to have survived and for
scientists to find traces of it.
Now a research team led by Brown University has found evidence of
carbonates, a long-sought mineral that shows Mars was home to a variety
of watery environments — some benign, others harsh — and that the
acidic bath the planet endured left at least some regional pockets
If primitive life sprang up in pockets that avoided the acidic transformation, clues for it may remain.
"Primitive life would have liked it," said Bethany Ehlmann, a Brown
graduate student and lead author of the paper that appears in the Dec.
19 edition of Science. "It's not too hot or too cold. It's not too
acidic. It's a 'just right' place.'
Finding carbonates indicates that Mars had neutral to alkaline
waters when the minerals formed in the mid-latitude region more than
3.6 billion years ago. Carbonates dissolve quickly in acid, therefore
their survival challenges suggestions that an exclusively acidic
environment later cloaked the planet.
The carbonates showed up in the most detail in two-dozen images
beamed back by the Compact Reconnaissance Imaging Spectrometer for
Mars, an instrument aboard the NASA Mars Reconnaissance Orbiter.
Scientists found the mineral near a trough system called Nili Fossae,
which is 667 kilometers (414 miles) long, at the edge of the Isidis
impact basin. Carbonates were seen in a variety of terrains, including
the sides of eroded mesas, sedimentary rocks within Jezero crater and
rocks exposed on the sides of valleys in the crater's watershed. The
researchers also found traces of carbonates in Terra Tyrrhena and in
NASA's Phoenix Mars Lander recently found carbonates in soil
samples, and researchers had previously found them in Martian
meteorites that fell to Earth and in windblown Mars dust observed from
orbit. However, the dust and soil could be mixtures from many areas, so
the origins of carbonates have been unclear. The latest observations
indicate carbonates may have formed over extended periods on early Mars
and also point to specific locations where future rovers and landers
could search for possible evidence of past life.
"This is opening up a range of environments on Mars," said John
"Jack" Mustard, a Brown professor of geological sciences and a
co-author on the Science paper. "This is highlighting an environment
that to the best of our knowledge doesn't experience the same kind of
unforgiving conditions that have been identified in other areas."
The researchers, including Brown graduate student Leah Roach and
scientists from NASA, the Johns Hopkins University Applied Physics
Laboratory, the Institut d'Astrophysique Spatiale at the University of
Paris, the U.S. Geological Survey, Cornell University and the
University of Nevada, have multiple hypotheses for how the
carbonate-bearing rocks were formed and the origin of the water that
shaped them. They may have been formed by slightly heated groundwater
percolating through fractures in olivine-rich rocks. Or, they may have
been formed at the surface when olivine-rich rocks were exposed and
altered by running water. Yet another theory is the carbonates
precipitated in small, shallow lakes. Either way, such environments
would have boded well for primitive life forms to emerge.
"We know there's been water all over the place, but how frequently
have the conditions been hospitable for life?" Mustard said. "We can
say pretty confidently that when water was present in the places we
looked at, it would have been a happy, pleasant environment for life."
NASA and the National Science Foundation funded the research.
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