[meteorite-list] Did a Nickel Famine Trigger the 'Great Oxidation Event'?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 13 May 2009 17:48:10 -0700 (PDT)
Message-ID: <200905140048.RAA02954_at_zagami.jpl.nasa.gov>

Carnegie Institution of Washington

Contact:
Dominic Papineau, 202-478-8908

April 8, 2009

Did a Nickel Famine Trigger the "Great Oxidation Event"?

Washington, D.C. -- The Earth's original atmosphere held very little oxygen.
This began to change around 2.4 billion years ago when oxygen levels
increased dramatically during what scientists call the "Great Oxidation
Event." The cause of this event has puzzled scientists, but researchers
writing in Nature[*] have found indications in ancient sedimentary rocks
that it may have been linked to a drop in the level of dissolved nickel in
seawater.

"The Great Oxidation Event is what irreversibly changed surface environments
on Earth and ultimately made advanced life possible," says research team
member Dominic Papineau of the Carnegie Institution's Geophysical
Laboratory. "It was a major turning point in the evolution of our planet,
and we are getting closer to understanding how it occurred."

The researchers, led by Kurt Konhauser of the University of Alberta in
Edmonton, analyzed the trace element composition of sedimentary rocks known
as banded-iron formations, or BIFs, from dozens of different localities
around the world, ranging in age from 3,800 to 550 million years. Banded
iron formations are unique, water-laid deposits often found in extremely old
rock strata that formed before the atmosphere or oceans contained abundant
oxygen. As their name implies, they are made of alternating bands of iron
and silicate minerals. They also contain minor amounts of nickel and other
trace elements.

Nickel exists in today's oceans in trace amounts, but was up to 400 times
more abundant in the Earth's primordial oceans. Methane-producing
microorganisms, called methanogens, thrive in such environments, and the
methane they released to the atmosphere might have prevented the buildup of
oxygen gas, which would have reacted with the methane to produce carbon
dioxide and water. A drop in nickel concentration would have led to a
"nickel famine" for the methanogens, who rely on nickel-based enzymes for
key metabolic processes. Algae and other organisms that release oxygen
during photosynthesis use different enzymes, and so would have been less
affected by the nickel famine. As a result, atmospheric methane would have
declined, and the conditions for the rise of oxygen would have been set in
place.

The researchers found that nickel levels in the BIFs began dropping around
2.7 billion years ago and by 2.5 billion years ago was about half its
earlier value. "The timing fits very well. The drop in nickel could have set
the stage for the Great Oxidation Event," says Papineau. "And from what we
know about living methanogens, lower levels of nickel would have severely
cut back methane production."

What caused the drop in nickel? The researchers point to geologic changes
that were occurring during the interval. During earlier phases of the
Earth's history, while its mantle was extremely hot, lavas from volcanic
eruptions would have been relatively high in nickel. Erosion would have
washed the nickel into the sea, keeping levels high. But as the mantle
cooled, and the chemistry of lavas changed, volcanoes spewed out less
nickel, and less would have found its way to the sea.

"The nickel connection was not something anyone had considered before," says
Papineau. "It's just a trace element in seawater, but our study indicates
that it may have had a huge impact on the Earth's environment and on the
history of life."

[*] Kurt O. Konhauser, Ernesto Pecoits, Stefan V. Lalonde, Dominic Papineau,
Euan G. Nisbet, Mark E. Barley, Nicholas T. Arndt, Kevin Zahnle & Balz S.
Kamber, Oceanic nickel depletion and a methanogen famine before the Great
Oxidation Event, scheduled for publication in Nature on 09 April, 2009.

IMAGE CAPTION:
[http://www.gl.ciw.edu/sites/www.gl.ciw.edu/files/u12/DSC02297small.jpg
(452KB)]
Banded iron formations like this from northern Michigan contain evidence of
a drop in dissolved nickel in ancient oceans.
Received on Wed 13 May 2009 08:48:10 PM PDT