Geology is an interesting science, because it allows reading Earth‘s history from what we found under our feet. For example, now scientists found that world’s richest ore deposits were formed because of rise of oxygen in the atmosphere 2.3 to 1.8 billion years ago. The same process helped the evolution of life too.
Iron, gold and nickel ore deposits were generally formed before zinc, silver, copper and uranium ore deposits. Scientists did not know what caused this shift and decided to conduct an international research, in which scientists from the University of Tasmania and University of California were working. What really made this research possible was laser-based analytical technology developed in the University of Tasmania laboratories, which allowed scientists to track the changes in oxygen levels in Earth’s atmosphere. This technology analyses the chemistry of pyrite (fools gold) that grew in seafloor muds billions of years ago, which allows determining how oxygen levels rose and declined over the years pretty accurately.
Then scientists looked at how oxygen levels correlated with ore deposits formed in that particular period. It turns out, giant ore deposits of gold, iron and nickel formed when oxygen was very low in the atmosphere and oceans. As the oxygen levels climbed up, the amount of sulphate and salt increased in crustal fluids and giant deposits of copper, zinc, silver and uranium started forming. Interestingly, the same rise in oxygen levels, commonly known as Great Oxygenation Event, contributed strongly to the evolution of life in our planet.
Australia’s biggest and richest ore deposits contain zinc, silver, copper and uranium ore and they were formed after this switch. But how does oxygen affect the formation of these ore deposits? Professor Ross Large, leader of the study, explained: “Copper, zinc, silver and uranium are readily mobile in oxygen-rich and salty crustal fluids, which were plentiful during middle Earth history, whereas gold and iron are only mobile in low oxygen crustal fluids, like the most ancient fluids, that preceded the Great Oxygenation Event”.
Scientists hope that they will find a way of using this knowledge to predict new places where valuable ore could be extracted. However, even without present practical application this research serves as an example of what can be found about Earth’s history from analysis using modern technology.
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