The layers of clay that in the past could have supported life on the surface of Mars would have been damaged by highly salty water, which would prevent the detection of possible signs of ancient living organisms on the planet, point out the authors of a study published in the Science magazine.
The researchers raised this hypothesis after analyzing observations made by NASA’s Curiosity rover, which has been studying the bottom of the crater – and ancient lake – Gale since 2012. By taking two samples of sediment layers from 3.5 billion years ago, the device discovered in one of them a concentration of clay minerals about two times lower than in the other, although they were collected only 400 meters away. Instead, that second sample contained high levels of iron oxides, the chemical compounds responsible for the color of the Martian surface.
According to the scientists, that composition may be due to the clay being destabilized and degraded by brine that seeped into the geological sediments after the lake dried up.
“We used to think that once those layers of clay minerals formed at the bottom of the lake in Gale Crater they stayed that way, preserving the moment of time when they formed over billions of years. But later brines decomposed those clay minerals in some places, essentially resetting the rock record, “quotes a statement from NASA’s Jet Propulsion Laboratory to lead author Tom Bristow.
At the same time, the findings show not only the destruction of signs of a possible ancient life, but also point to the possible existence of organisms under the ground due to the action of groundwater that dissolve and transport chemicals, changing the structure of sediments. On Earth, that process, known as diagenesis, has created deep microbial habitats and could have done the same on Mars, scientists say.
For Bristow co-author John Grotzinger, the deep biospheres “are excellent places to look for evidence of ancient life and measure habitability.”
“Although diagenesis can erase the signs of life in the original lake, it creates the chemical gradients necessary to support underground life, so we are very excited to have discovered this,” he explains.
The information obtained by Curiosity will be used in the future to select the most promising rocks for possible traces of Martian life.