Scientists have discovered bizarre evidence in the US state of Wyoming – that bacteria hidden deep within the Earth's crust secrete uranium.
Uranium, the silvery white metal known for its radioactive properties and usage in nuclear power plants, is thought to occur within ore deposits in the form of uraninite. The uranium in this form is usually mined from sandstone "roll-front" deposits.
But the latest findings published in Nature Communications challenge long-held beliefs about the way uranium can be formed. Geologists now believe uranium is produced biologically, in a series of chemical reactions in Earth's crust that take place over millions of years.
A team of biogeochemists has spotted promising signs that living microorganisms can also produce uranium, albeit in a different form than in the mineral uraninite. By analyzing the composition of uranium from 650-foot-deep samples mined in Wyoming – and using synchotron radiation-based spectroscopy and isotope fingerprinting – they found that 89 per cent of the uranium was bound to inorganic carbonate instead of being in uraninite ore.
The deposits match up to a series of biochemical reactions present in dissimilatory metal-reducing bacteria, a class of microbes that oxidize organic matter and produce metals in the process of anaerobic respiration. In other words, the bacteria use uranium instead of oxygen for energy.
"You know you might have a big story when you discover something that will result in people having to rewrite textbooks," said Thomas Borch, co-author of the paper and professor of soil and crop sciences at Colorado State University.
"Our results may introduce a paradigm shift in the way we think about ore genesis and mining – from implications for human health, to restoration practices, to how mining companies calculate how much they can earn from a given site."
The biologically produced uranium can be mined, and is probably easier to mine compared to uraninite ores, since it's more soluble, Borch told The Register. This might be good news for mining companies but its bad news for environmentalists, as it means it could end up contaminating drinking water sources.
The team hopes to investigate if other roll-front deposits in other parts of the world are similar to the one found in Wyoming, to determine how common the process is and if the bacteria today are the same as those found in Earth's crust three million years ago. ®