Scientists knew prior to the rover mission that spherical concretions, as they are called, exist on Earth. A new study suggests they can learn more about the history of water on Mars -- and possibly life -- by studying the hard spheres in the Southwestern desert.
Similar and different
There are similarities and differences in these rocky spheres from two worlds. The Martian type seem to be pure hematite, an oxide of iron that is gray, instead of the common red color associated with rust.
The Utah blueberries are made of cemented sandstone -- the red rock common to the Southwest. Typically no more than one-third of their contents is hematite, and many have just a few percent hematite. They're thought to have formed about 25 million years ago.
As on Mars, the heavy blueberries on Earth tend to congregate in natural bowls, cracks and depressions. One such spot at the Opportunity landing site on Mars was dubbed the Berry Bowl.
"Before Opportunity landed, we thought there might be hematite concretions on Mars," said Marjorie Chan, a geologist at the University of Utah. "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 spheres have been found near Moab and in the Zion National Park, among other locations. Chan led a new analysis of them that appears in the June 17 issue of the journal Nature.
How they formed
On Earth and Mars, the blueberries formed out of rock that was loaded with iron.
"Fluids travel through these rocks and leach out the iron," explained University of Utah graduate student Brenda Beitler. "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."
The rock-hard blueberries of Utah were used for games of marbles by ancestral moqui, according to Hopi legend, says said University of Washington scientist David Catling, who wrote an analysis of the new research for the journal. New Age adherents trade them as moqui marbles -- a term discouraged by anthropologists -- and claim they have metaphysical powers.
"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," Catling said.
Scientists wonder whether biological activity might have played a role in the formation of spheres on either planet. Bacteria on Earth can cause concretions to form more rapidly, scientists say. Chan's team plans to investigate the Utah marbles for signs of past microbial activity.
Scientists studying the Martian concretions have found no evidence of life, past or present.
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