"The link between green rust, nickel uptake and the oxygenation history of the planet requires further investigation, but our finding is a major step forward," study researcher Simon Poulton, a professor of biogeochemistry at Newcastle University in the United Kingdom, told LiveScience in an email.
Green rust, like the better-known, red-orange stuff, is an iron mineral, first identified only about a decade ago, according to Poulton.
Since then, green rust, which is indeed a pale green, has been found in only a few places, including water-logged soils, groundwater, and, now, the oxygen-free water of Lake Matano in Indonesia. The deep waters of this ancient lake contain iron-rich and oxygen-free waters like those scientists believe filled Earth's deep oceans more than 580 million years ago. (In Living Color: Gallery of Stunning Lakes)
The discovery of green rust in the lake suggests this rare mineral may have been more common in Earth's ancient past, Poulton said.
Like other iron minerals, green rust readily absorbs dissolved elements onto its surface, but green rust is not only particularly efficient at this - in many cases, it can also react with toxic dissolved trace metals to make them insoluble, and as a result, renders them in nontoxic forms. This is something most normal iron oxides cannot do, Poulton said.