A sample collected by NASA's Perseverance rover of reddish rock, formed billions of years ago from sediment on the bottom of a lake, contains potential signs of ancient microbial life on Mars, according to scientists. 

However, the minerals identified in the sample can also form through nonbiological processes. The discovery by the six-wheeled rover in Jezero Crater is one of the strongest pieces of evidence so far supporting the idea that Earth's planetary neighbor may have once harbored life.

Since landing on the Martian surface in 2021, the rover has been exploring Jezero Crater, an area in the planet's northern hemisphere that was once flooded with water and housed an ancient lake basin, as it searches for signs of ancient life. 

Perseverance has been collecting samples of rock and loose material called regolith and analyzing them with its various onboard instruments. The rover obtained the newly described sample, called the Sapphire Canyon sample, from a location called the Bright Angel rock formation. 

This formation consists of fine-grained mudstones and coarse-grained conglomerates, a type of sedimentary rock made of gravel-sized particles cemented together by finer sediments. Stony Brook University planetary scientist Joel Hurowitz, who led the study published in the journal Nature, said a "potential biosignature" was detected in multi-billion-year-old sedimentary rocks.

This appeared as two minerals that seem to have formed through chemical reactions between the mud of the Bright Angel formation and organic matter also present there, Dr. Hurowitz explained. They are vivianite, an iron phosphate mineral, and greigite, an iron sulfide mineral. 

However, Dr. Hurowitz offered some caution. "The reason, however, that we cannot claim this is more than a potential biosignature is that there are chemical processes that can cause similar reactions in the absence of biology, and we cannot rule those processes out completely based on rover data alone," he said.

Mars has not always been the harsh environment it is today, with liquid water present on its surface in the distant past. Scientists have suspected that microbial life once existed in Jezero Crater, believing that river channels overflowed the crater wall and created a lake more than 3.5 billion years ago. The Sapphire Canyon sample was collected in July 2024 from rocky outcrops on the edges of Neretva Vallis, an ancient river valley carved by water flowing into Jezero Crater. 

The sample analyzed by Perseverance offers a new example of a potential biosignature that researchers can explore to determine whether these features were formed by life or if, alternatively, nature has created features that mimic biological activity, Dr. Hurowitz said. "Ultimately, follow-up research will provide us with a set of testable hypotheses to evaluate whether biology is responsible for these features in the Bright Angel formation, which can be tested if the Sapphire Canyon sample is returned to Earth," he added.