-- The tiny, round ``blueberries'' found on Mars by NASA's Opportunity rover strongly support the theory that water once drenched the vast Meridiani Planum region the six-wheeled robot has been exploring, scientists said. Analysis showed that the spheres are mostly hematite, which is typically formed in water The finding was made at ``Berry Bowl,'' a depression where enough of the tiny spheres collected to allow the rover's Mossbauer spectrometer to distinguish the composition of the so-called berries from the background rock. ``This is the fingerprint of a hematite,'' said Rodionov, a graduate student from the University of Mainz in Germany and a member of the team running the Mossbauer, a device that identifies iron-bearing minerals such as hematite. The ``blueberries'' -- which are actually gray -- are believed to be mineral ``concretions'' that form within rocks due to water action and then fall out onto the Martian surface as rock weathers away.
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.
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.
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.
Concretions, preferentially cemented masses within sediments and sedimentary rocks, are records of sediment diagenesis and tracers of pore water chemistry. For over a century, rinded spheroidal structures that exhibit an Fe(III) oxide–rich exterior and Fe-poor core have been described as oxidation products of Fe(II) carbonate concretions. However, mechanisms governing Fe(III) oxide precipitation within these structures remain an enigma. Here we present chemical and morphological evidence of microbial biosignatures in association with Fe(III) oxides in the Fe(III) oxide–rich rind of spheroidal concretions collected from the Jurassic Navajo Sandstone (southwest United States), implicating a microbial role in Fe biomineralization.
The direct association of Fe(III) oxides with microbial fossils implicates microorganisms in Fe(III) oxide biomineralization during the oxidative dissolution of Fe(II) carbonate. This process is not limited to spheroidal concretions; we have identifi ed various structures within the Navajo Sandstone, such as pipe-like concretions and joint-associated boxworks (Loope et al., 2011, 2012), that similarly display an Fe(III) oxide–rich rind with an Fe-poor core. This process is likely operative in modern saturated environments including aquifers on Earth as well as on Fe-rich rocky planets bearing siderite such as Mars (Michalski and Niles, 2010). Iron oxide concretions with an Fe(III) oxide–rich exterior and an iron-poor core therefore offer a macroscopic target in the search for life on Earth as well as Mars.
The circular patch on the rock in the picture is where the rock abrasion tool (RAT) of the Mars Rover was used to brush away dust prior to analysis by Opportunity’s spectrometers. This analysis showed the rock was composed of different chemicals to the spherules that were found to be rich in hermatite. So the Mars Blueberries were strong, immediate evidence of the past presence of water on Mars.
UWA scientists David Wacey and Matt Kilburn used high-resolution NanoSIMS technology at the University's Centre for Microscopy, Characterisation and Analysis to show clear relationships in the Utah concretions between microbe-like forms and concentrations of biological elements such as carbon and nitrogen. Read more at: phys.org...
Together these results indicate that autotrophic microorganisms were present during Fe(III) oxide precipitation and present microbial catalysis as a mechanism of Fe(III) oxide concretion formation. Microbial biosignatures in rinded Fe(III) oxide–rich concretions within an exhumed, Quaternary aquifer has broad implications for detection of life within the geological record on Earth as well as other Fe-rich rocky planets such as Mars, where both Fe(II) carbonate and Fe(III) oxide–rich concretions have been identified.