Evidence of ancient life on Mars was “wiped out,” scientists say, when NASA’s Curiosity rover found that portions of the Red Planet’s rock record had been removed.
Mars has a large number of ancient rocks and minerals compared to Earth, and to gain more knowledge about the history of the planet, scientists sent Curiosity into Mars’ storm crater.
The crater has dried up for billions of years, and scientists have evidence that super-saline water (brine) seeped through the cracks in the lake floor, altering the minerals below.
Using the CheMin tool (Chemistry & Mineralogy X-Ray Diffraction), the scientists compared samples from two areas that were approximately 400 meters apart. Surprisingly, they found that half of the clay minerals expected in an area were missing; they were replaced by claystones rich in iron oxide, which give Mars its red color.
It is likely that the salty water filtered through superimposed layers of sediment is what caused the rock records to disappear. The salty water likely comes from lakes that existed when Mars was drier, as opposed to the freshwater lakes that would have been present when the mudstones were formed.
“We used to think that these layers of clay minerals that formed at the bottom of the lake in Gale Crater stayed that way and kept the moment they formed for billions of years,” said Tom Bristow , CheMin’s chief researcher at Nasa Ames Research Center, in a statement. “But later brines mined these clay minerals in some places – and thus essentially set the rock record back.”
Scientists believe these results show the effects of climate change on Mars that occurred eons ago. Already, NASA knew that before the lakes of Gale Crater dried up, the groundwater had gone below the surface, dissolving and hiding chemicals that scientists could study.
After these minerals were deposited, the mudstone changed due to interactions with them in a process known as “diagenesis,” which impedes or obliterates the ability of scientists to understand the history of the soil. However, this also creates an underground experience that could support microbial life – known on Earth as “deep biospheres”.
“These are excellent places to look for evidence of ancient life and measure habitability,” said John Grotzinger, co-investigator with CheMin at the California Institute of Technology. âAlthough diagenesis can erase the signs of life in the pristine lake, it creates the chemical gradients necessary to support life below the surface. We are very happy to have discovered this. “
The scientists said they were lucky enough to find both mudstones so close together because they can use mineralogy to determine which part of the Martian rock lights our search for extraterrestrial life and which doesn’t.
This information can also be used by NASA’s Mars 2020 Perseverance Rover team to evaluate and select rock samples that could be returned to Earth.