Nickel Famine May Have Led To Life On Earth

The evolution of complex life-forms on Earth, from parakeets to panthers, could occur only after oxygen gas appeared in our atmosphere more than 2 billion years ago. But scientists have long debated how oxygen-producing bacteria could have gained dominance over methane-producing bacteria, and in so doing, taken control of the composition of primordial Earth's air. Now, a team of researchers led by Kurt O. Konhauser, a biogeochemist at the University of Alberta, in Edmonton, report evidence that this turning point in the history of life on Earth may be rooted in an ancient nickel famine (Nature 2009, 458, 750). In particular, the team found that the nickel-to-iron ratio in ancient rocks dropped around 2.7 billion years ago. Because methane-producing bacteria rely heavily on nickel for many of their essential enzymes, a deficiency of the metal could have decreased the metabolism and populations of methane makers, giving oxygen-evolving microbes the necessary edge. "If a single geological change can starve a major microbial community, and thereby change the trajectory of life on Earth, it suggests that there is a fragility to Earth's elemental cycles that we are only beginning to uncover," notes Mak A. Saito of Woods Hole Oceanographic Institution, in a commentary that accompanies the report.