This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The origins of the earliest life on Earth, prior to the rise of oxygen and photosynthesis, remain a mystery. Graveyards in brine pools at the bottom of the Red Sea may hold some answers.
Brine pools are underwater ponds or lakes that sit at the bottom of the sea. They're dark, full of salt and devoid of oxygen. For years, they were presumed to be lifeless.
But research revealed that for certain extremophiles, these brine pools aren't inhospitable: They're oases. The bacteria and archaea that thrive there leave geochemical signatures long after they're gone, Morgan Chakraborty and colleagues show in a new study published in AGU Advances. The researchers analyzed the geochemical composition of sediments and organic matter in an active brine pool, three non-brine seafloor spots, and a spot they suspected was an "extinct" brine pool based on mineral rings around a depression filled with dead marine organisms.
They used metagenomics and metatranscriptomics to characterize the microbial communities at the sites. The active pool, 1,770 meters (5,810 feet) below the surface of the Red Sea, was teeming with bacteria and archaea. The sediments under the microbial mat were extremely enriched in metals like manganese, iron, molybdenum and copper, with some areas hosting concentrations upward of 100 times higher than their non-brine pool counterparts.
The extinct pool, nearly 1,400 meters (4,600 feet) below the sea surface, had similar enrichment patterns. The presence of oxidized manganese and molybdenum-enriched organic matter in the sediments of both the active and extinct brine pools will improve interpretations of similar patterns in the rock record. Metagenomic analyses of the active pool revealed manganese oxidizers such as Nitrospira.
That finding, together with oxidized iron-manganese phases in the sediment, offers some evidence that microbial oxidation of Mn(II) to manganese oxides could have served as a mechanism for energy production prior to the rise of atmospheric oxygen during the Great Oxidation Event around 2.4–2.2 billion years ago. Overall, though the authors note that more research is needed, the findings support hypotheses that metal enrichment in the early oceans could have occurred independently of oxygenic photosynthesis or photoautotrophy. Chemotrophic oxidation of manganese and iron could well have been the engine of the earliest life in the oceans.
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