2022-04-28 | Dr Craig O'Neill | Did the destabilisation of deep primordial mantle drive the Great Oxidation Event?

Craig O'Neill

Did the destabilisation of deep primordial mantle drive the Great Oxidation Event?

Speaker: Dr Craig O’Neill

Date: 28th of April 2020

Location: QUT Garden’s Point

Abstract:

The rise of Earth’s atmospheric O2 levels at ~2.4Ga, known as the Great Oxidation Event or GOE, was driven by a shift between increasing sources and declining sinks of oxygen. Here we compile recent evidence that the mantle shows a significant increase in oxidation state leading to the GOE, linked to the sluggish upward mixing of a deep primordial oxidised layer. Such an oxidised layer is expected from magma ocean crystallisation models, which suggest disproportionation of ferropericlase drove the oxidisation state of the deep mantle up. Additionally, this deep mantle was enriched in bridgmanite, with higher viscosity than the ambient mantle.  We simulate the evolution of this deep layer by implementing a new rheological model for this oxidised, bridgmanite-enriched viscous material and demonstrate slow mantle mixing rates in simulations of early Earth’s mantle. The eventual homogenisation of this layer may take ~2Gyr, in line with the timing of the observed mantle redox shift, and would result in the increase in upper mantle oxidation of > 1 log(fO2) unit. Such a shift would alter the redox state of volcanic degassing products to more oxidised species, removing a major sink of atmospheric O2, and allowing oxygen levels to rise at ~2.4Ga.

Details:

Location: QUT Gardens Point
Start Date: 28/04/2022 [add to calendar]
Start Time: 11:00
End Date: 28/04/2022
End Time: 12:00