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SGS Speaker Series - Dr. Kurt Konhauser - Tracing the Evolution of Oxygen on the Ancient Earth
Tue., Dec. 6, 2022 12:00 a.m. - Tue., Dec. 6, 2022 1:00 p.m.
Location: Bushwakker Brewpub, 2206 Dewdney Ave, Regina
If you plan to attend in person at Bushwakker Brewpub, please RSVP for lunch by 6 pm on Sunday December 4
This seminar is part of the Saskatchewan Geological Society Fall Speaker Series.
Speaker: Dr. Kurt Konhauser, University of Alberta, 2021 Geological Association of Canada Logan Medallist
Title: Tracing the Evolution of Oxygen on the Ancient Earth
Date and time: Tuesday December 6, 2022, 12 noon (CST)
Location: in person at Bushwakker Brewpub, 2206 Dewdney Ave, Regina
Online: https://uregina-ca.zoom.us/j/95479433567?pwd=cXdYSmNldi9zdW43dTJsV1JLaE5PUT09
Abstract:
A remarkably coherent ensemble of evidence points to a significant accumulation of atmospheric oxygen for the first time in Earth’s history beginning ca. 2.45 Ga, the so-called Great Oxidation Event (GOE). Briefly, this includes the disappearance of detrital pyrite, uranitite and siderite from fluvial and deltaic deposits, an increase in the retention of iron in paleosols, an enrichment of Cr and U in iron formations, and perhaps most importantly, the disappearance of sedimentary sulphur isotope mass-independent (S-MIF) anomalies indicative of atmospheric SO2 processing in the absence of appreciable ozone. However, several trace element and isotopic proxies have recently suggested oxidative weathering hundreds of millions of years earlier1-2. The superposition of pre-GOE signals for oxidative weathering at a time of global anoxia represents a conundrum for which the most accepted explanation is that pre-GOE oxidative weathering is the result of transient oxygenation events (the so-called ‘whiffs’) by driven oxygen oases in the marine realm. Lalonde and Konhauser3proposed an alternative model, that being intense O2 generation – and immediate consumption – at sub-meter scales by benthic oxygenic photosynthesis in the terrestrial realm. Despite the absence of a UV-protective ozone layer in the Archean, a terrestrial phototrophic biosphere may have existed in various sheltered environments, including biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculated that the rate of O2 production via oxygenic photosynthesis in these ecosystems provides sufficient oxidising potential to mobilise sulphate and a number of redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. An intriguing question that follows from this hypothesis is if cyanobacteria were conceivably metabolising at modern rates on land by perhaps 3.0 Ga, what happened in the hundreds of million years between the first, rare signals of oxidative weathering and the first significant accumulation of atmospheric oxygen, i.e., the GOE? While the exact confluence of factors controlling the success of Earth’s earliest oxygenic phototrophs remains an open question4, several factors may have depressed areal coverage or photosynthetic efficiency of cyanobacteria, and thus masked their potential presence prior to the GOE, including the lack of colonisable surface area for oxidative weathering.
[1] Crowe et al (2013), Nature 501, 535-539.
[2] Planavsky et al (2014), Nature Geoscience 7, 283-286.
[3] Lalonde and Konhauser (2015), PNAS 112, 995-1000.
[4] Planavsky et al (2021), Nature Reviews: Earth and Environment 2:123-139.