Scientists possess limited knowledge regarding the oceanic conditions during the dawn of life, but recent research in Nature Geoscience sheds light on how geological processes governed the availability of vital nutrients crucial for early life development.
All organisms rely on nutrients like zinc and copper for synthesizing proteins. The most ancient life forms emerged during the Archean Eon, approximately three and a half billion years before the first appearance of dinosaurs. These early microbes displayed a preference for metals such as molybdenum and manganese, unlike their more contemporary counterparts. This inclination is believed to mirror the prevalence of metals in the ancient oceans.
A collaborative team from the University of Cape Town (UCT) and the University of Oxford replicated ancient seawater conditions within a laboratory setting. Their study revealed that greenalite, a commonly found mineral in Archean rocks, swiftly forms and absorbs zinc, copper, and vanadium during this process. As greenalite developed in the early oceans, these metals were extracted from seawater, leading to an abundance of other metals like manganese, molybdenum, and cadmium. Interestingly, the metals projected to be most prevalent in Archean seawater align with those favored by early life forms, elucidating why they were preferred during initial evolutionary stages.
Lead researcher Dr Rosalie Tostevin (University of Oxford at the time of the study, now Senior Lecturer in the Department of Geological Sciences at UCT), said: “We were very excited when we noticed that our results match predictions from biologists who use a completely different approach. It is always reassuring when specialists in other fields are making similar findings.”
Scientific consensus agrees that Archean seawater significantly differed from present-day conditions, characterized by higher dissolved iron and silica content and negligible oxygen levels. However, consensus is lacking concerning other facets of seawater chemistry, such as nutrient concentrations.
“We can’t go back in time to sample seawater and analyse it, so reconstructing Archean conditions is quite a challenge. One approach is to look at the chemical makeup of sedimentary rocks, but the chemistry of very old rocks has sometimes been altered. We instead decided to create a miniature version of ancient seawater in the laboratory, where we could directly observe what was happening,” said Tostevin.
Tostevin and colleague Imad Ahmed recreated Archean seawater within an oxygen-free chamber and monitored the formation of greenalite. They observed substantial shifts in metal concentrations within seawater as the minerals formed. Utilizing X-ray absorption spectroscopy at the Diamond Light Source synchrotron, they confirmed the integration of metals into the minerals, while other metals remained unaffected, persisting at elevated levels in seawater.
Tostevin said: “We know that greenalite was important on the early Earth because we keep finding it in old rocks, such as the iron ore in the Northern Cape, South Africa, and similar rocks in Australia. We think this may have been one of the most important minerals in the Archean. But we don’t know exactly how greenalite was forming in nature. One possibility is that greenalite formed deep in the ocean at hydrothermal vents. But it could also have formed in shallow waters, wherever there was a small change in pH.” Tostevin and Ahmed decided to run their experiments under both types of conditions and found that regardless of how greenalite forms, it removes metals in a similar way.
The researchers pondered whether the metals would remain sequestered or eventually return to seawater over time. To investigate, they subjected the minerals to heat, simulating natural burial and crystallization processes. The metals persisted within the mineral, suggesting a long-term storage mechanism that significantly influenced ancient seawater chemistry.
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