Wednesday, 27 April 2011
Dr Boswell Wing from Earth and Planetary Sciences, McGill University will introduce the S MIF proxy for p O 2 and describe the gross constraints that it provides on atmospheric anoxia through Earth history.
Canonical wisdom holds that Earth's history of atmospheric oxygen is essentially binary. The secular evolution of oxygen partial pressure ( p O 2 ) is inferred from records of reduced detrital minerals, oxidized paleosols, banded iron formation, and more recently, mass-independent fractionation (MIF) of sulfur isotopes; all point to a significant increase in p O 2 at ≈2.4 Ga. The most quantitative constraint on this timeline comes with the loss of S MIF, which requires p O 2 <10 -5 present atmospheric levels for its production and preservation. To date, it has been widely assumed that this threshold was never crossed in the Archean and that Archean-like levels of atmospheric O 2 never returned after the Paleoproterozoic ‘great oxidation event'. Dr Boswell Wing will present a pair of case studies - one from mid-Archean strata associated with voluminous volcanic eruptions and one from ca. 635 Ma rocks associated with a low-latitude glaciation - that call into question a simple binary interpretation of atmospheric anoxia.
WHEN: Thursday 5 May 2011, 4pm-5pm
WHERE: CMCA Seminar Room, Level 1, Physics Building
CONTACT: Dana Crisan (Centre for Microscopy, Characterisation and Analysis) (+61 8) 6488 2770
Refreshments provided.
Media references
Janine MacDonald (UWA Public Affairs) (+61 8) 6488 5563 / (+61 4) 32 637 716
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