for National Geographic News
Scientists used NASA's Mars Reconnaissance Orbiter to take a close look at clays on the Martian surface known to be associated with water. (See pictures previously gathered by the orbiter.)
The telltale clays—called phyllosilicates—were found to be scattered broadly across the planet's surface in craters, valleys, delta formations, and dunes.
That means water existed in a variety of terrains, the scientists say.
"It wasn't this hot, boiling cauldron," said lead author Jack Mustard, a planetary geologist at Brown University.
"It was a benign, water-rich environment for a long period of time," he said.
The new study appears in this week's issue of the journal Nature.
The wet-era Martian clays were first reported in the December 2005 issue of Nature by French scientist François Poulet and colleagues.
"There had been this thought that there were pockets, but how extensive was it?" Mustard asked. He and his team—which includes Poulet—documented a diverse assemblage of minerals deposited by water, including kaolinite, chlorite, and hydrated silica, all of which occur in a pattern that indicates a waterlogged Martian crust.
"People like to think of lakes and oceans, but the crust is where early life may have started," Mustard said. "There was tons and tons of water that was just percolating through the crust."
The watery era on Mars appears to have ended abruptly. Olivine—a mineral that breaks down in the presence of water—was deposited atop the clays in a still-visible layer on the surface.
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