Geologist Michael Tice had never lost sleep over a Mars rock before. That changed as he dug into data from the red planet’s Bright Angel rock formation, located in an ancient river valley called Neretva Vallis.
This rock formation contains the most compelling evidence to date for possibility of ancient life on Mars, scientists say, citing a new analysis of samples collected by NASA’s Perseverance rover published September 10 in the journal Nature. Further research is needed to confirm that life indeed existed there, but for scientists like Tice and his collaborator Joel Hurowitz, the rocks of Bright Angel raise the possibility that microbes thrived in the mud underwater some 3.5 billion years ago.
“It’s pretty mind blowing,” says Tice, a research scientist at Texas A&M University and co-author of the new study. “When Joel and I started seriously considering the possibility that life could have been involved in forming these things, I had trouble sleeping that night.”
Bright Angel’s rocks, on the western edge of Jezero Crater, were likely deposited at the bottom of a lake or river when water flowed freely on a planet that is now dry. Chemical clues suggest that a specific type of reaction occurred in these rocks, and on Earth, such reactions typically involve microbial life.
“This is the first time that chemical processes consistent with—though not definitive proof of—a biological origin have been observed” on Mars, says Christian Schröder, a physicist at the Max Planck Institute for Solar System Research, who was not involved in the study.
NASA’s Perseverance Mars rover used its Mastcam-Z instrument to view the area around the sample collected from a rock nicknamed “Cheyava Falls.” Composite Photograph by NASA/JPL-Caltech/ASU/MSSS
Poppy Seeds and leopard spots
Throughout Bright Angel, Perseverance found greenish specks scientists like to call “poppy seeds” or “nodules” embedded in reddish mudstone. Prominent in those specks is the mineral vivianite containing iron phosphate.
The rover also drilled a thin rock core sample called Sapphire Canyon, barely as long as an adult pinky finger. Sapphire Canyon showed tiny ring-like features called “leopard spots” with rims made of dark minerals that are also iron phosphate, and lighter interior areas with an iron sulfide mineral called greigite.
(Learn about other Mars rocks aiding the search for life.)
What’s most exciting for the search for life would have occurred at a scale even smaller than molecules. In an oxidation-reduction or “redox reaction,” organic material gave over electrons to iron in the mud and left these other minerals, vivianite and greigite, behind.
On Earth, microorganisms spark reactions like this by consuming the organic matter and capturing the energy released in the redox process, with minerals formed as biproducts. It’s like kind of like how humans eat food to gain energy, and generate waste, too.
“The places where we see that happening on Earth, in ambient-temperature, sedimentary settings, those reactions are typically driven by microbes,” said Hurowitz, a geologist at Stony Brook University.
If the Bright Angel formation results ultimately do lead to the proof of ancient life on Mars, Tice notes, that means two different planets hosted microbes getting their energy through the same means at about the same time in the distant past. That could suggest that early life learns how to survive in this way regardless of where it originated. “I think that could be telling us something really profound about how life evolves,” he says.
Cheyava Falls was found in an ancient riverbed within the “Bright Angel” region of Mars’ Jezero Crater, which contained “leopard spots.” Photograph by NASA/JPL-Caltech/MSSS
How to prove it was life
Proving that a sign of life, or what scientists call a biosignature, has been found definitively is an enormous scientific undertaking. It requires multiple lines of evidence, from different scientific instruments, and a thorough investigation of the geological context in which the biological signal could have been produced. Enormous amount of scrutiny and debate would ensure before such a ground-breaking conclusion.
The obvious first question is: Can a non-biological source produce the same result?
The same redox reactions described in the Mars rock paper, with the same biproducts, can occur without the presence of life, but only under hot conditions. A volcanic eruption could theoretically explain something like this, no life required. But the study authors believe conditions weren’t hot enough in this particular location when the rocks seem to have been underwater.
“If you were to take the mud and the organic matter and cook them, you could come up with that same set of minerals,” Hurowitz says. “But so far, using all the tools available to us, we don’t see any evidence that these rocks were heated up to the kinds of temperatures that would be needed to make that reaction happen.”
What’s more, Tice noted that if a massive lava flow event had created the leopard spots they would only appear in a single layer, rather than multiple layers of the core sample.
Scientists stressed that to know for sure whether ancient microbial life was responsible for the poppy seeds and leopard spots in Sapphire Canyon, samples of Mars rocks would need to be returned to Earth so that scientists can use more sophisticated laboratory equipment to more thoroughly investigate. The fate of NASA’s own sample return program remains up in the air, however.
In the meantime, the European Space Agency’s Rosalind Franklin rover could also push the story of life on Mars forward. It will drill deeper into the red planet’s surface and analyze samples on the red planet. Samples from farther underground would be better preserved from the harsh surface environment, notes Schröder, who is affiliated with the project. Named for a key collaborator in the discovery of the DNA double helix, ESA’s rover is expected to launch in 2028.
To rule out explanations other than life, scientists need to also explore more environments on Earth that have characteristics similar to those of ancient Mars, Hurowitz says, to see if there are examples of similar chemical reactions happening without the involvement of biology. These could include the bottoms of lakes, estuaries, and other areas where rocks are immersed in water.
(Why signs of life on Mars remain so mysterious)
Is this the first possible evidence of life on Mars?
In July 2024, NASA first announced that the arrowhead-shaped rock called Cheyava Falls, named for the tallest waterfall in the Grand Canyon. With white veins of calcium sulfite, the rock had chemical signatures and structures that, billions of years ago, could have been forged by life. Those included carbon-based molecules fundamental to biology, but which could also come from non-biological sources. The Sapphire Canyon core sample described in the new study comes from Cheyava Falls.
This isn’t the first time that a Mars rover has found possible signs of ancient habitablity and conditions that could point to life. The Spirit rover, for example, found an ancient hot spring environment at Gusev Crater before getting stuck in sand and losing contact. The Curiosity rover, which is still operating today at Gale Crater, found organic compounds in mudstones there.
But telltale signs of redox reactions elevate this new finding above the environmental clues that other Mars rovers have found , Schröder says.
As for whether this is the most interesting rock beyond Earth, Hurowitz hesitates, but adds, “if your specific interests are astrobiology and geobiology, this is a pretty darn good candidate for favorite rock.”