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June 16, 2004 -- Even before marble-shaped pebbles
nicknamed “blueberries” were discovered on Mars by
the Opportunity rover, University of Utah geologists studied similar
rocks in Utah’s national parks and predicted such stones
would be found on the Red Planet.
In a study published in the June 17 issue of the journal Nature,
the Utah researchers suggest both the Martian and Utah rocks –
known as hematite concretions – formed underground when
minerals precipitated from flowing groundwater.
“We came up with the ‘recipe’ for blueberries,”
says Marjorie Chan, chair and professor of geology and geophysics
at the University of Utah. “Before Opportunity landed, we
thought there might be hematite concretions on Mars. That was
based on our study of hematite-rich regions of southern Utah,
where hematite balls are found in national parks and have long
been a geological oddity that shows up in many rock shops.”
The round rocks are found in southern Utah in Zion and Capitol
Reef national parks, Grand Staircase-Escalante National Monument,
Snow Canyon State Park and the Moab area.
Their diameters range from one-25th of an inch to 8 inches or
more. They are known to New Agers as “moqui marbles.”
Some are the size of small blueberries like those on Mars.
Chan and her colleagues believe the Utah concretions formed perhaps
25 million years ago when minerals precipitated from groundwater
flowing through much older Navajo sandstone, the spectacular red
rock in southern Utah.
The National Aeronautics and Space Administration’s Opportunity
robot rover vehicle landed on Mars’ Meridiani Planum on
Jan. 25. Five days later, it detected hematite within gray pebbles
dotting the landing site, and such pebbles later were spotted
embedded in a rock outcrop. Cornell University scientist Steve
Squyres, who heads the Opportunity science team, said Feb. 9 the
small spheres look “like blueberries in a muffin”
and might be concretions.
In their Nature paper, Chan and colleagues say the Martian
“blueberries” may have formed in a similar manner
to those in Utah, namely, when significant volumes of groundwater
flowed through permeable rock, and chemical reactions triggered
minerals to precipitate and start forming a layered, spherical
ball.
“Given the similarities between the marbles in Utah and
on Mars, additional scientific scrutiny of the Utah concretions
and how they form will probably shed further light on the similar
phenomenon on Mars,” University of Washington scientist
David Catling wrote in a Nature commentary accompanying
the University of Utah study.
The concretions may bear on the search for evidence of past life
on Mars because bacteria on Earth can make concretions form more
quickly. Chan and colleagues plan to analyze whether there is
evidence of past microbial activity in Utah concretions.
Chan conducted the new study with geology graduate student Brenda
Beitler and emeritus professor of geology Bill Parry, both at
the University of Utah; geologist Jens Ormo of the National Institute
of Aerospace Technology in Madrid, Spain; and planetary scientist
Goro Komatsu of the International Research School of Planetary
Sciences at G. d'Annunzio University in Pescara, Italy.
Martian blueberries and marbles of the spirits
The Utah and Mars hematite concretions have similarities and differences.
In Utah and likely on Mars, “you have rocks that had iron
in them originally,” says Beitler. “Fluids travel
through these rocks and leach out the iron. The water moves through
cracks, holes, layers or pores until it reaches some place where
the chemistry is different and causes the iron to precipitate
out of the water as hematite.”
A major difference is that the Martian “blueberries”
probably are pure hematite – a form of iron oxide that is
gray because it has a larger crystal structure than the reddish
form of iron oxide, commonly known as rust. The Utah concretions
are mostly sandstone, cemented by hematite that makes up a few
percent to perhaps one-third of the rock. The Martian concretions
likely precipitated from acidic groundwater. Those in Utah precipitated
when hydrocarbon-rich, briny fluids encountered oxygen-rich groundwater.
After the Utah concretions formed in groundwater, the surrounding
Navajo sandstone slowly eroded away over millions of years, so
the hard, erosion-resistant concretions accumulated on the ground,
often in great numbers.
“The loose Utah concretions roll like marbles into depressions,
forming ‘puddles,’ just like their Martian counterparts,”
Catling wrote. “The Hopi Indians have a legend that ‘moqui,’
or spirits of their ancestors, played games of marbles with the
hematite concretions in the American southwest. Although anthropologists
discourage use of the word ‘moqui’ to be respectful
to Native Americans, New Age gem collectors sell concretions as
‘moqui marbles’ and claim that they are endowed with
metaphysical powers.”
Hematite, water and life
In 1998, the Mars Global Surveyor orbiting Mars detected what
appeared to be a large area of hematite on Meridiani Planum. The
broad plain was picked as Opportunity’s landing site because
scientists wanted to study the hematite, which almost always forms
in water.
Scientists are interested in whether water once existed on Mars
(or now exists beneath its surface) because water is necessary
for life – and the possibility of life beyond Earth is one
of the great questions long pondered by humanity.
“On Earth, whenever we find water, we find life –
in surface water or underground water, hot water or cold water
– any place there is water on Earth there are microbes,
there is life,” says study co-author Bill Parry. “That’s
the bottom line: hematite is linked to life.”
While other evidence from Opportunity suggests there once may
have been standing water on Meridiani Planum, the Utah team’s
study strongly indicates the Martian “blueberries”
probably formed in groundwater and not in surface water.
“The ‘blueberries’ easily could have formed
in groundwater before there was standing water, if that did exist,”
Chan says.
Other scientists previously offered various explanations for Meridiani
Planum’s hematite, including that the mineral precipitated
in large lakes or in hot springs when Mars’ ancient volcanoes
were active, or that hematite was left when water leached away
other minerals, or that it formed when volcanic ash deposits were
altered chemically.
Like Southern Utah, Like Mars
Chan says her team long suspected concretions like those in Utah
might be found on Mars. The idea first was suggested by Ormo and
Komatsu in a 2003 scientific abstract that got little if any attention.
Ormo contacted Chan in spring 2003 and they started collaborating.
The researchers completed a much broader but yet-unpublished study
last year indicating that several geological features were seen
both in aerial photos of southern Utah’s hematite-rich areas
and in images of Mars’ hematite regions taken by orbiting
spacecraft. These features include large rocky landforms shaped
like knobs, pipes and buttes, and places where bleached-looking
rock forms white sediment beds or ring-shapes on the surface.
Some of the pipes and other features are tens of yards long or
wide.
The geologists determined the processes responsible for these
large-scale features in Utah involved the flow of briny groundwater
saturated with natural gas that bleaches sandstone, and that such
groundwater flow, the precipitation of hard hematite-cemented
rock and the later erosion of surrounding softer rock also would
explain the formation of the erosion-resistant pipes, buttes,
knobs and concretions. They concluded a similar process could
have formed concretions and larger landforms on Mars.
Chan says studying concretions from Utah and Mars “will
help us learn more about the history of Mars. When we have something
to compare it to, it’s a lot easier to figure out.”
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