Paleosols (ancient fossilized soils) filling the Yellowknife Bay geologic formation within the 3.7-billion-year-old Gale Crater on Mars are strong evidence that the planet was once much warmer and wetter, says geologist Dr Gregory Retallack of the University of Oregon, based on images recently released by NASA.

“The images, taken by NASA’s Curiosity Mars rover, reveal Earth-like soil profiles with cracked surfaces lined with sulfate, ellipsoidal hollows and concentrations of sulfate comparable with soils in the Antarctic Dry Valleys and the Chile’s Atacama Desert,” Dr Retallack said.

He identified two new types of Martian soil – the Yila paleosol (named after the woman who dreamed of arriving astronauts in the Ray Bradbury’s Martian Chronicles, 1950) and the Spender paleosol (named after the archaeologist in the same novel).

“Their dating to 3.7 billion years ago puts them into a time of transition from an early benign water cycle on Mars to the acidic and arid Mars of today.”

Yila and Spender paleosols do not prove that the Red Planet once contained life, but they do add to growing evidence that an early Mars was more habitable than the planet has been in the past 3 billion years.

“The new data show clear chemical weathering trends, and clay accumulation at the expense of the mineral olivine, as expected in soils on Earth,” explained Dr Retallack, who reported the findings in the journal Geology.

“Phosphorus depletion within the profiles is especially tantalizing, because it attributed to microbial activity on Earth.”

“Life on Earth is believed to have emerged and began diversifying about 3.5 million years ago, but some researchers have theorized that potential evidence that might take life on Earth farther back was destroyed by plate tectonics, which did not occur on Mars.”

_____

Gregory J. Retallack. Paleosols and paleoenvironments of early Mars. Geology, published online July 14, 2014; doi: 10.1130/G35912.1