The Earth’s atmosphere has undergone several stages of progressive oxygenation throughout its history which has had profound effects on the behaviour and availability of metals on the Earth’s surface, and the biosphere. A broad range of geological and geochemical evidence has been used to reconstruct the stages of the atmosphere’s oxygenation. However, there is a large gap in data between ~1.8 and 0.8 Ga, leading to the assumption that there were only minor changes in the oxygen content of the atmosphere during that time. Most geological and geochemical data from this stage, known as the ‘boring billion’, is derived from rocks deposited in deep-marine environments, which had little interaction with the atmosphere. During the boring billion the Earth’s crust was undergoing a period of hitherto unparalleled continental assembly, forming the supercontinent Rodinia. Crustal differentiation following the amalgamation of Rodinia caused the concentration of metals in the upper crust. Such a large continental mass also allowed intracontinental basins to form resulting in the deposition of terrestrial sedimentary successions, which have much greater interaction with the atmosphere than those deposited in deep environments. Thus terrestrial rocks of boring billion age are more likely to contain geochemical evidence of the atmospheric oxygen content than their deep marine counterparts. One such succession is the Torridonian Supergroup of NW Scotland. Analysis of the facies and metal deposits from varied depositional environments within the Torridonian and other contemporaneous terrestrial successions as part of this study has yielded evidence suggesting the atmosphere and surface environment was considerably more oxygenated, and that metal availability in the surface environment was much greater during the boring billion than previously thought. Furthermore, evidence in this study suggests the biosphere had adapted to inhabit an oxygen-rich terrestrial environment, evolved to utilise increasing availability of trace metals, and had a critical role in the concentration of metals in the Earth’s surface during the mid-Proterozoic.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569603 |
| Date | January 2012 |
| Creators | Spinks, Samuel C. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=192185 |
Page generated in 0.0116 seconds