martian landscape
July 19, 2014

Curiosity Rover Images Show Martian Soils That Are Similar To Earth’s

April Flowers for - Your Universe Online

A new study from University of Oregon (OU) geologist Gregory Retallack suggests that soil samples taken by NASA's Mars Curiosity rover contain evidence that Mars was once much warmer and wetter. His findings, published online in Geology, are based on images and data of 3.7 billion year old soil collected in the Gale crater.

Previous rovers have revealed the Martian landscape is littered with loose rocks created by impacts or layered by catastrophic floods. These formations are in contrast to the smooth contours of soils that soften the landscapes of Earth. Retallack says that recent Curiosity images, however, reveal Earth-like soil profiles. The profiles have cracked surfaces lined with sulfate, ellipsoidal hollows and concentrations of sulfate comparable with soils in Antarctic Dry Valleys and Chile's Atacama Desert.

Retallack is the co-director of paleontology research at the UO Museum of Natural and Cultural History, as well as being an international expert on the recognition of paleosoils — ancient fossilized soils contained in rocks. For this study, he analyzed mineral and chemical data published by researchers with close ties to the Curiosity mission.

"The pictures were the first clue, but then all the data really nailed it," Retallack said in a recent statement. "The key to this discovery has been the superb chemical and mineral analytical capability of the Curiosity Rover, which is an order of magnitude improvement over earlier generations of rovers. The new data show clear chemical weathering trends, and clay accumulation at the expense of the mineral olivine, as expected in soils on Earth. Phosphorus depletion within the profiles is especially tantalizing, because it attributed to microbial activity on Earth."

Retallack cautions that his results do not prove the Red Planet once held life. Rather, he sees his results as adding to the growing pile of evidence that Mars was not always the arid and inhospitable planet that it has been for the last 300 billion years.

Currently, Curiosity is exploring regions of Gale Crater that are topographically higher and geologically younger. The soils in these layers appear to be less conducive to life. Retallack would like to see more missions to Mars that explore older, and more clay-like, terrains.

Curiosity's images include surface cracks, which suggest typical soil clods. Vesicular hollows (rounded holes) and sulfate concentrations found on Mars are both features of desert soils on Earth, according to Retallack.

"None of these features is seen in younger surface soils of Mars," Retallack said. "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 believes the newly discovered soils provide evidence of a more benign and habitable Mars. Dating the soils to 3.7 billion years ago puts them in the transitional period between "an early benign water cycle on Mars to the acidic and arid Mars of today." Most scientists believe that life on Earth began to emerge and diversify approximately 3.5 million years ago. Some, however, have hypothesized that potential evidence could push that timeline farther back. They believe this evidence was destroyed by tectonic activity, which does not occur on Mars.