Scientists know very little about conditions in the ocean when life first evolved, but new research published in the journal All life uses nutrients such as zinc and copper to form proteins. The oldest lifeforms evolved in the Archean Eon, three and a half billion years before the dinosaurs first appeared. These microbes showed a preference for metals such as molybdenum and manganese compared to their more recent counterparts. This preference is thought to reflect the availability of metals in the ocean at that time.
Research Findings on Ancient Seawater
Researchers from the University of Cape Town (UCT) and the 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.”
Challenges in Understanding Archean Seawater
Scientists agree that the Archean seawater was very different from today, with more dissolved iron and silica and little to no oxygen. However, there is little agreement about other aspects of seawater chemistry, such as the concentration of nutrients.
“We can’t go back in time to sample seawater and analyze 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.
Exploring Greenalite Formation
Tostevin and her colleague Imad Ahmed recreated Archean seawater inside a special oxygen-free chamber and watched as greenalite began to form. They observed dramatic changes in the metal concentrations in seawater as the minerals formed. They used X-ray adsorption Spectroscopy at the
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.
One question that concerned the researchers was whether the metals would be locked up for a long time or released back into seawater after several months or years. To test this, they heated the minerals to emulate what happens in nature when they are buried and undergo crystallization. The metals remained trapped in the mineral, suggesting this was a permanent sink for metals that would have profoundly impacted early seawater.
Reference: “Micronutrient availability in Precambrian oceans controlled by greenalite formation” by Rosalie Tostevin, and Imad A. M. Ahmed, 13 November 2023, Nature Geoscience.
DOI: 10.1038/s41561-023-01294-0