Science & Technology, UK (Commonwealth Union) – Our understanding of the conditions in the ocean during the emergence of life remains limited, but a recent study published in Nature Geoscience has shed light on how geological processes influenced the availability of crucial nutrients for early life development.
In the evolutionary timeline, the oldest life forms emerged during the Archean Eon, a staggering three and a half billion years prior to the appearance of dinosaurs. These ancient microbes exhibited a distinct preference for metals like molybdenum and manganese over their more contemporary counterparts, such as zinc and copper. This preference is believed to be linked to the abundance of metals in the ancient oceans during that period.
Researchers from the University of Cape Town (UCT) and the University of Oxford undertook a groundbreaking initiative to recreate ancient seawater conditions in the laboratory. Their experiments revealed that greenalite, a mineral commonly found in Archean rocks, rapidly forms and extracts zinc, copper, and vanadium in the process. As greenalite developed in the early oceans, these metals would have been sequestered from seawater, resulting in an enrichment of other metals like manganese, molybdenum, and cadmium. Interestingly, the metals identified as most prevalent in Archean seawater align with those favored by early life forms, providing a compelling explanation for their prevalence during the initial stages of evolution.
Lead researcher Dr. Rosalie Tostevin, formerly affiliated with the University of Oxford and now a Senior Lecturer in the Department of Geological Sciences at UCT, expressed enthusiasm about the study’s findings, noting the alignment with predictions made by biologists using a different approach. This convergence of results across diverse fields adds a layer of confidence to the research.
While there is consensus among scientists that Archean seawater differed significantly from its contemporary counterpart, characterized by elevated levels of dissolved iron and silica and a lack of oxygen, disagreements persist regarding other aspects of seawater chemistry, including nutrient concentrations. This study contributes valuable insights into the intricate interplay between geological processes and the availability of essential nutrients during the crucial period when life first emerged in Earth’s ancient oceans.
“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,” explained Tostevin.
Within a controlled, oxygen-free chamber, Dr. Rosalie Tostevin and her collaborator, Imad Ahmed, meticulously replicated Archean seawater conditions. The intriguing experiment unfolded as greenalite, a distinctive mineral, started to take shape. During this process, the researchers witnessed significant alterations in the concentrations of metals within the seawater. To substantiate their observations, they employed X-ray Absorption Spectroscopy at the Diamond Light Source synchrotron, conclusively demonstrating the incorporation of certain metals into the developing minerals. Conversely, other metals remained unaffected by this mineralization process, persisting at elevated levels in the seawater.
Tostevin elaborated further “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 as well as Ahmed chose to carry out their experiments under both types of conditions discovering that regardless of the way greenalite forms, it takes away metals in a similar way.
