Ancient Soil on Mars Suggests Microbial Life

Ancient soil in a crater dating back some 3.7 billion years suggests that Mars was once much warmer and wetter, and possibly harbored microbial life, according to a new study.

NASA's Curiosity rover recently captured images of the deep impact Gale Crater, which revealed Earth-like soil with cracked surfaces containing ellipsoidal hollows and concentrations of sulfate comparable with soils in Antarctic Dry Valleys and Chile's Atacama Desert.

Observations in previous research have shown Martian landscapes littered with loose rocks from impacts or layered by catastrophic floods, but never the smooth contours of soils like those on Earth.

As described in the journal Geology, lead author Gregory Retallack, a geologist with the University of Oregon, studied mineral and chemical data published by researchers closely tied with the Curiosity mission.

"The pictures were the first clue, but then all the data really nailed it," Retallack said in a statement. "The key to this discovery has been the superb chemical and mineral analytical capability of the Curiosity Rover."

The data, he says, shows clear chemical weathering trends and clay accumulation at the expense of the mineral olivine, characteristics like that of Earth-like soil.

"Phosphorus depletion," Retallack added, "within the profiles is especially tantalizing, because it attributed to microbial activity on Earth."

Though the findings are promising, the ancient soils do not prove that Mars once contained life. They do, however, add to growing evidence that the red Planet was once warmer, wetter, and more habitable than it has been for the past 3 billion years.

"The exploration of Mars, like that of other planetary bodies, commonly turns up unexpected discoveries, but it is equally unexpected to discover such familiar ground," Retallack said.

Curiosity rover is now exploring topographically higher and geologically younger layers within the crater, where the soils appear less conducive to life. To unearth a more detailed record of Mars soil, new missions will be needed to explore its ancient terrain.

On July 10, the Curiosity rover rolled into new territory for the first time, leaving its "safe" terrain to enter new and unexplored parts of the Gale Crater as part of its landing and exploration mission.