A shortage of nickel in the oceans of ancient Earth may be the push that gave oxygen-producing bacteria a competitive edge over their methane-producing counterparts. The long-term result: an oxygen-rich atmosphere, and life as we know it.

The findings, reported yesterday in Nature, provide a new answer to the long-standing question of how ‘Great Oxidation Event’ occurred 2.4 billion years ago. Kurt Konhauser of the University of Alberta in Canada and his colleagues analyzed the nickel-to-iron ratio of banded iron formations found in sedimentary rock (pictured at right). They found that nickel levels dropped dramatically around 2.7 billion years ago, possibly because cooling of the Earth’s crust reduced the nickel-content of volcanic rocks.

Methane-producing bacterial rely heavily on three critical nickel-containing enzymes, so when the abundance of nickel declined, so did they. Methane reacts with oxygen in the atmosphere, and with less methane being produced, oxygen released by the world’s earliest photosynthesizers was free to accumulate and reshape the planet. For more, check out Chemistry World, National Geographic, or Science News.