Brine pools at the bottom of the Red Sea may offer important clues about the origins of early life on Earth, before the rise of oxygen and photosynthesis. These brine pools are underwater lakes or ponds found on the seafloor, known for their extreme conditions—complete darkness, high salt content, and the absence of oxygen. For a long time, scientists believed these environments were barren, but recent research has revealed that certain types of microbes, called extremophiles, can survive and even flourish in these harsh conditions. A new study published in AGU Advances by Morgan Chakraborty and colleagues examined the geochemical and biological characteristics of brine pools and other seafloor areas in the Red Sea. The team analyzed sediments and organic matter from an active brine pool, three non-brine seafloor sites, and a location that may have once been a brine pool, now considered "extinct" due to the presence of mineral rings around a depression filled with dead marine life. Using advanced techniques such as metagenomics and metatranscriptomics, the researchers identified the microbial communities present at these sites. The active brine pool, located 1,770 meters (5,810 feet) below the surface of the Red Sea, was found to be rich in bacteria and archaea. The sediments beneath the microbial mat were extremely high in metals like manganese, iron, molybdenum, and copper, with some areas containing concentrations up to 100 times greater than those found at non-brine pool sites. Similar metal enrichments were also observed in the extinct pool, located nearly 1,400 meters (4,600 feet) below the sea surface. These findings could help scientists better understand similar patterns found in the geological record of Earth's ancient rocks. Metagenomic analyses of the active pool revealed the presence of bacteria that can oxidize manganese, such as Nitrospira. Combined with the presence of oxidized iron and manganese compounds in the sediments, these findings suggest that microbial oxidation of manganese could have been a way for early life to generate energy before the rise of atmospheric oxygen, during a period known as the Great Oxidation Event, which occurred around 2.4 to 2.2 billion years ago. The study highlights that metal enrichment in the early oceans might have occurred without the presence of oxygenic photosynthesis. This research supports the idea that the chemical oxidation of metals like manganese and iron could have been a key driver of the earliest life in Earth's oceans. More studies are needed to confirm and expand on these findings.