Evidence of ancient life on Mars has been ‘erased’, Nasa scientists say

Some of the rock record of the Red Planet has been washed away by supersalty brine, essentially ‘resetting’ it, Nasa says

Evidence of ancient life on Mars has been ‘erased’, scientists say, as Nasa’s Curiosity rover has found parts of the Red Planet’s rock record has been removed.

Mars has a huge number of ancient rocks and minerals compared with the Earth, and in order to try and gather more knowledge about the history of the planet scientists sent Curiosity into Mars’ Gale Crater.

The crater has been dried out for billions of years, and scientists have evidence that supersalty water (brines) seeped through the cracks in the lake bottom and altered the minerals below it.

Using the CheMin (Chemistry & Mineralogy X-Ray Diffraction) tool, scientists compared samples taken from two areas approximately 400 meters from each other. Surprisingly, they discovered that half of the clay minerals they expected to find in one area were missing; they were replaced with mudstones rich with iron oxides, which give Mars is red colour.

It is likely that the briny water filtered through overlaying sediment layers is the reason why the rock record has disappeared. The salty water likely originated from lakes that existed when Mars was drier, unlike the freshwater lakes which would have been present when the mudstones formed.

“We used to think that once these layers of clay minerals formed at the bottom of the lake in Gale Crater, they stayed that way, preserving the moment in time they formed for billions of years,” said Tom Bristow, CheMin principal investigator at Nasa’s Ames Research Center, in a statement. “But later brines broke down these clay minerals in some places – essentially resetting the rock record.”

Scientists believe these results show the impacts of Mars’ climate change, which took place eons ago. Nasa already knew that before Gale Crater’s lakes dried out its groundwater had moved beneath 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 complicates or erases scientists’ ability to understand the soil’s previous history. This also, however, 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 gauge habitability,” said John Grotzinger, CheMin co-investigator at the California Institute of Technology. “Even though diagenesis may erase the signs of life in the original lake, it creates the chemical gradients necessary to support subsurface life, so we are really excited to have discovered this.”

The scientists said they were fortunate to be able to find both mudstones so close together, as they can use minerology to tell which part of the Martian rock will illuminate our search for alien life and which will not.

This information can also be used by Nasa’s Mars 2020 Perseverance rover team, to evaluate and select rock samples for that could be returned to Earth.