Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event

• Published in: Nature Vol. 458; no. 7239; pp. 750 - 753
• Main Authors: Konhauser, Kurt O., Pecoits, Ernesto, Lalonde, Stefan V., Papineau, Dominic, Nisbet, Euan G., Barley, Mark E., Arndt, Nicholas T., Zahnle, Kevin, Kamber, Balz S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.04.2009; Nature Publishing Group
• Subjects: Atmosphere - chemistry; Banded iron formations; Chemical oceanography; Chemical properties; Earth Sciences; Earth, ocean, space; Environmental aspects; Euryarchaeota - metabolism; Exact sciences and technology; Famine; Geologic Sediments - chemistry; Humanities and Social Sciences; Hydroxides; Iron; Iron - analysis; letter; Marine; Methane; Methanobacteriaceae; Microorganisms; Mineralogy; multidisciplinary; Nickel; Nickel - analysis; Nickel - metabolism; Oceans; Oceans and Seas; Oxidation; Oxidation-Reduction; Oxidation-reduction reaction; Oxygenation; Precambrian; Ratios; Rocks; Science; Science (multidisciplinary); Sciences of the Universe; Seawater; Seawater - chemistry; Seawater - microbiology; Stratigraphy; Studies; Sulfate reduction; Sulfates; Trace elements; Trends; Upper mantle; Canada; depletion; partition coefficients; oxides; bacteria; production; oxidation-reduction conditions; enzymes; sulfates; Precambrian; chemical ratios; paleoatmosphere; oxygen; BIF; sulfides; nickel; oxidation; upper mantle; weathering; concentration; igneous rocks; metamorphic rocks; hydroxides; prokaryotes; biogenic origin; ocean; chemical reduction; microorganisms; plutonic rocks; methane; cooling; iron; Archean; ultramafics
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature07858

Whys after the Event The Great Oxidation Event (GOE), an era on Earth about 2.4 billion years ago when oxygen began to accumulate in the atmosphere, is widely thought to have been triggered by a decrease in atmospheric methane levels. What could have caused methane to start to disappear has remained uncertain. Now based on the discovery of a decline in the molar nickel to iron ratio in banded iron formations, sedimentary rocks laid down about 2.7 billion years ago, Konhauser et al . offer a new hypothesis to explain the loss of methane. They attribute the scarcity of nickel to a reduced flux of nickel to the oceans due to a fall in upper mantle temperatures and a decreased eruption of nickel-rich ultramafic rocks at that time. Nickel is a key cofactor in several enzymes found in methanogens, so its decline may have stifled the activity of methane producing organisms in the ancient oceans and disrupted the supply of biogenic methane. A decrease in atmospheric methane levels might have triggered the progressive rise of atmospheric oxygen about 2.4 billion years ago, but the cause of this methane decrease remains uncertain. Kurt Konhauser and colleagues report a decline in the oceanic nickel-to-iron ratio about 2.7 billion years ago, which they attribute to a reduced flux of nickel to the oceans; this decline would have stifled the activity of methane-producing organisms that require nickel to function. It has been suggested that a decrease in atmospheric methane levels triggered the progressive rise of atmospheric oxygen, the so-called Great Oxidation Event, about 2.4 Gyr ago 1 . Oxidative weathering of terrestrial sulphides, increased oceanic sulphate, and the ecological success of sulphate-reducing microorganisms over methanogens has been proposed as a possible cause for the methane collapse 1 , but this explanation is difficult to reconcile with the rock record 2 , 3 . Banded iron formations preserve a history of Precambrian oceanic elemental abundance and can provide insights into our understanding of early microbial life and its influence on the evolution of the Earth system 4 , 5 . Here we report a decline in the molar nickel to iron ratio recorded in banded iron formations about 2.7 Gyr ago, which we attribute to a reduced flux of nickel to the oceans, a consequence of cooling upper-mantle temperatures and decreased eruption of nickel-rich ultramafic rocks at the time. We measured nickel partition coefficients between simulated Precambrian sea water and diverse iron hydroxides, and subsequently determined that dissolved nickel concentrations may have reached ∼400 nM throughout much of the Archaean eon, but dropped below ∼200 nM by 2.5 Gyr ago and to modern day values 6 (∼9 nM) by ∼550 Myr ago. Nickel is a key metal cofactor in several enzymes of methanogens 7 and we propose that its decline would have stifled their activity in the ancient oceans and disrupted the supply of biogenic methane. A decline in biogenic methane production therefore could have occurred before increasing environmental oxygenation and not necessarily be related to it. The enzymatic reliance of methanogens on a diminishing supply of volcanic nickel links mantle evolution to the redox state of the atmosphere.