Decline in nickel kick-started evolution

Life as we know it may owe its existence to the decline in metal on the early earth.

Last Updated: 8:17AM BST 09 Apr 2009

The massive influx of oxygen into Earth's atmosphere some 2.4 billion years ago that set evolution on a path to multicellular life was unleashed by a cascade of events in which nickel played a starring role.
What scientists call the Great Oxygen Event "irreversibly changed surface environments on Earth and ultimately made advanced life possible," said Dominic Papineau of the Carnegie Institution's Geophysical Laboratory and a co-author of the study.

"It was a major turning point in the evolution of our planet."
Scientists generally agree that this oxygen surge was made possible by a rapid decline in atmospheric levels of methane.
But why methane dropped off has remained a mystery.
The researchers, led by Kurt Konhauser of the University of Alberta in Edmonton, Canada, believe the answer lies in rocks that were formed before oxygen was abundant in the air or the sea.
Analysing changes over time in the level of trace elements in these rocks, the scientists noticed that levels of nickel dropped just before oxygen levels soared.
This piece of evidence led them to fit all the pieces of theoretical puzzle together.
The dominant life form before the Great Oxygen Event was the methanogen - a single-celled ocean organism that exuded methane as a byproduct of its metabolism.
The enormous quantities of methane these methanogens produced almost certainly prevented the build up of oxygen in the air.
To survive, these creatures gobbled up nickel, which existed 2.7 billion years ago in quantities 400 times greater than today.
By 2.5 billion years ago, nickel levels in the oceans had dropped by more than half.
Starved of this nutrient, the methanogens declined and their output of methane plummeted.
This cleared the way for a class of photosynthesising life forms and ocean plants.