Recent research conducted by Xinming Chen and his team at Shanghai Jiao Tong University has unveiled significant insights into the early stages of ocean oxygenation. They compared well-preserved ancient shales from Australia and South Africa. via Adam Simon Their study of thallium concentrations indicated the ocean had become at least regionally oxygenated between 2.65 billion and 2.5 billion years ago. This study provides important context for a pivotal period in Earth’s history when single-celled organisms first started to change the planet’s atmosphere.
This evidence indicated that atmospheric oxygen levels increased for the first time during the Great Oxidation Event, 2.4 billion years ago. This dramatic increase was primarily fueled by the photosynthetic works of cyanobacteria. These microorganisms were extremely successful during this time. They performed a key service to our planet, oxygenating Earth’s atmosphere roughly between 2.4 billion years and 2.1 billion years ago, according to research supporting a 2.5-billion-year-old episode of global oceanic oxygenation discovered by Chen’s team. This event is in agreement with other oxygenation events discovered by an independent research group in an adjacent Australian shale formation.
Kurt Konhauser, a leading geobiologist, noted the creative evolutionary genius of cyanobacteria. He emphasized that they were extremely common and promoted the oxygenation even in the seafloor. Geochemical analyses of sediments from 2.6 billion years ago show that these oxygen explosions probably flooded huge regions of the primordial ocean. If truly representative, this means oxygen levels dropped drastically at points over that period.
Recent discoveries in ancient, primitive seafloor sediments suggest cyanobacteria started photosynthesizing hundreds of millions of years before the Great Oxidation Event. Yet this remarkable period of evolution, perhaps more than any other event in the history of our planet, set the stage for life on Earth. To do what Chen’s team did—find evidence of widespread, regional oxygenation in the oceans. To achieve this ambitious goal, they sampled thallium isotopes in ancient shales.
In this search for extraterrestrial life, Chen’s research group is using a technique that would change the game. This new approach pinpoints biosignatures associated with past oxygen concentrations. Kurt Konhauser, who led the follow-up work on manganese oxides, suggested they could be the only thing responsible for producing these thallium signatures. If confirmed, this finding would represent a highly desirable biosignature warranting further investigation.
The research findings suggest that cyanobacteria were more widespread than previously believed during this era, contributing significantly to Earth’s atmospheric changes. Evidence includes hundreds of mound-shaped stromatolites found in shallow waters, which are layered formations primarily constructed by cyanobacteria, the first photosynthesizers on Earth.
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