A recent study co-authored by Dr. Michael Tice, a geologist from Texas A&M University, has uncovered chemical clues that hint at the possibility of ancient microbial life on Mars. These clues were revealed through rocks analyzed by NASA’s Perseverance rover.
The research, conducted by a large team of international scientists, focuses on a section of Jezero Crater known as the Bright Angel formation. This name is inspired by locations in the Grand Canyon National Park due to the light-colored Martian rocks found there. The area within Mars’ Neretva Vallis channel is rich in fine-grained mudstones, which contain oxidized iron (rust), phosphorus, sulfur, and—most intriguingly—organic carbon. While organic carbon, which can also come from non-living sources like meteorites, has been detected on Mars before, this unique combination of materials may have served as a considerable energy source for early microorganisms.
“When the rover explored Bright Angel and began analyzing the local rock compositions, the team noticed that they differed significantly from previous findings,” said Tice, who specializes in geobiology and astrobiology in the Department of Geology and Geophysics. “They exhibited chemical cycling, which is something organisms on Earth can use to produce energy. Upon closer inspection, we encountered features that can easily be explained by early Martian life, but are challenging to attribute solely to geological processes.”
Tice added, “Living organisms conduct chemistry that would naturally occur over time given the right conditions. However, based on our current knowledge, some of the chemicals that formed these rocks likely required either high temperatures or life. We don’t see evidence of high temperatures here, but our findings call for further experimentation and ultimately laboratory testing of the samples back on Earth to eliminate any explanations that do not involve life.”
The study’s results were published in Nature.
A window into Mars’ watery past
The Bright Angel formation is made up of sedimentary rocks shaped by water, including mudstones and layered beds that indicate a dynamic environment with flowing rivers and standing water. With the assistance of Perseverance’s sophisticated instruments, such as the SHERLOC and PIXL spectrometers, scientists detected organic molecules and arrangements of minerals that seem to have formed through “redox reactions,” which involve the transfer of electrons. On Earth, such processes are often a result of biological activities.
Among the most notable features are tiny nodules and “reaction fronts,” affectionately nicknamed “poppy seeds” and “leopard spots” by the rover team. These structures are enriched with ferrous iron phosphate (likely vivianite) and iron sulfide (likely greigite). These minerals typically originate in low-temperature, water-rich environments and are often linked to microbial activity.
“It’s not just the minerals; it’s their arrangement that suggests they formed through the redox cycling of iron and sulfur,” Tice explained. “On Earth, similar formations occur in sediments where microbes consume organic matter and ‘breathe’ rust and sulfate. Their existence on Mars prompts an intriguing question: could comparable processes have taken place there?”
Organic matter and redox chemistry
The SHERLOC instrument discovered a Raman spectral feature known as the G-band, a marker of organic carbon, in various Bright Angel rocks. The clearest signals originated from a location dubbed “Apollo Temple,” where both vivianite and greigite were in greatest abundance.
“The presence of organic matter alongside redox-sensitive minerals is highly compelling,” Tice suggested. “It implies that organic molecules may have influenced the chemical reactions that produced these minerals.”
It’s crucial to note that “organic” does not inherently indicate the involvement of living organisms.
“It simply refers to having numerous carbon-carbon bonds,” he clarified. “Other processes can create those bonds apart from life. The organic matter found here could stem from abiotic processes or could originate from life. If it resulted from life, the organic matter would have needed to break down through chemical reactions, radiation, or heat to create the G-band we observe today.”
The research outlines two possibilities: one where the reactions occurred abiotically, driven by geochemical processes, and another where microbial life influenced them, much like on Earth. Notably, while some features of the nodules and reaction fronts could arise from abiotic reactions, the known geochemical processes that typically produce sulfur-associated features tend to happen at relatively high temperatures.
“All methods we have used to analyze these rocks indicate they were not subjected to temperatures high enough to create the leopard spots and poppy seeds,” Tice remarked. “If that’s the case, we must seriously entertain the idea that they were formed by organisms, such as bacteria, that thrived in mud in a Martian lake over three billion years ago.”
Although the team emphasizes that the evidence is not definitive proof of past life, their findings align with NASA’s criteria for “potential biosignatures”—characteristics that merit further investigation to ascertain whether they are of biological or abiotic origin.
A sample worth returning
Perseverance has collected a core sample from the Bright Angel formation, named “Sapphire Canyon,” which is currently stored in a sealed tube onboard the rover. This sample is a priority for future return missions to Earth.
“Bringing this sample back to Earth would enable us to analyze it with instruments much more sensitive than anything we can deploy on Mars,” Tice stated. “We could investigate the isotopic composition of the organic material, the fine-scale mineral structure, and even search for microfossils if they exist. We would also be able to conduct more tests to determine the maximum temperatures these rocks experienced and whether high-temperature geochemical processes might still be the leading explanation for the potential biosignatures.”
Tice, who has extensively studied ancient microbial ecosystems on Earth, noted the striking similarities between Martian and terrestrial processes—along with one significant difference.
“It’s fascinating how life may have utilized similar processes on both Earth and Mars around the same time,” he explained. “We observe microorganisms reacting with iron and sulfur alongside organic matter in rocks of the same age on Earth, but we could never see the exact same features we observe on Mars in our own ancient rocks. Plate tectonics has altered our rocks too much to preserve them in this way. It’s truly spectacular to witness such formations on another planet.”
Summary: A new study led by Dr. Michael Tice suggests potential signs of ancient microbial life on Mars. Analyzed rocks from the Bright Angel formation reveal organic carbon and minerals that indicate chemical processes possibly linked to early life. While the findings are intriguing, they require further investigation and analysis, particularly through the samples collected by the Perseverance rover.
