HUNGRY nickel-grabbing bacteria could be to thank for the surge in atmospheric oxygen 2.5 billion years ago that made Earth hospitable to life.
Stefan Lalonde of the University of Alberta in Edmonton, Canada, and colleagues measured the concentration of nickel deposited in layered sedimentary rocks, or 鈥渂anded iron formations鈥�. They found that levels had dropped by two-thirds in the 200 million years prior to the 鈥淕reat Oxygenation Event鈥�.
The team speculate that this drop in nickel starved primordial ocean-dwelling bacteria called methanogens that used dissolved nickel in seawater to help turn food into energy and methane. As methane reacts with oxygen to remove it from the atmosphere, a decline in the methane produced by bacteria would have led to a build-up of oxygen.
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Though it is not clear quite how much the ancient bacteria relied on the metal, 鈥済rowing modern methanogens in the lab requires extremely high concentrations of nickel鈥�, says Stephen Zinder at Cornell University in Ithaca, New York.
So what could have caused the nickel shortage? A surge in the number of magma plumes just before the nickel decline removed a large amount of heat from Earth鈥檚 core, say the team. In these cooler conditions, more oceanic crust was created relative to continental crust. This contains less of the nickel that the bacteria can use. The work was presented at the American Geophysical Union meeting in December.
鈥淭his study is one of the first to look at hard data about metal concentrations, which is an important new idea,鈥� says Timothy Lyons of the University of California, Riverside. But he suspects the oxygenation effect may be less than the team thinks, because the bacterial famine could have enabled other atmospheric reactions that used up oxygen.
