Studying Microbial Mats to Understand Ancient Biosignatures
A recent study supported in part by the NASA Exobiology Program provides further details about lipid biomarkers in stromatolites. The research focuses on microbial mat communities in ponds at Guerrero Negro, Baja California Sur, Mexico.
Microbial mats play an important role in forming geological features known as stromatolites. These are rocky mounds built up over time as mats trap and interact with sediment. Stromatolites can be found in environments like Guerrero Negro today, but these structures also appear in the geologic record of the Earth. In fact, ancient stromatolite structures could be the oldest physical evidence of life on Earth yet known, and provide important clues about the early environment of our planet and the evolution of life as we know it.
Identifying ancient stromatolites is difficult however, because the composition of ancient microbial mats and the affects they had on sediment is unknown. In addition, these structures are incredibly old and have been altered over time by numerous geological and chemical processes. Studying the role of modern-day microbial mats in the formation of stromatolite structures can help researchers interpret potential evidence of similar structures in the geologic record of Earth.
The mats at Guerrero Negro inhabit gypsum deposits, and show distinct layers of pigment in cross-section. Researchers studied the fixation and flow of carbon through these structured layers in order to better understand the changes that potential biosignatures undergo. At each layer of the structure, different populations of microorganisms alter molecules that could be used as signatures of life. The first step is primary production of microbial lipids. As the lipids move down the layers, they are degraded by different microbial groups, including fermenters, sulfate reducers, and methanogens.
The study, “Carbon isotopic composition of lipid biomarkers from an endoevaporitic gypsum crust microbial mat reveals cycling of mineralized organic carbon,” was published in the journal Geobiology. The work was supported by NASA Astrobiology through the Exobiology Program. The research is a critical part of NASA’s work to understand the Universe, advance human exploration, and inspire the next generation. As NASA’s Artemis program moves forward with human exploration of the Moon, the search for life on other worlds remains a top priority for the agency.