HR: 1340h
AN: V43C-1436    [Abstracts]
TI: Neoproterozoic Land Colonisation, Rising Oxygen, Global Cooling and the Cambrian Explosion
AU: * Lenton, T M
EM: t.lenton@uea.ac.uk
AF: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ United Kingdom
AU: Watson, A J
EM: a.watson@uea.ac.uk
AF: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ United Kingdom
AB: The Neoproterozoic (1000-542 Ma BP) was a time of severe glaciations and a major transition from microscopic to macroscopic life forms. We develop the hypothesis that a rise in atmospheric oxygen in the Neoproterozoic was driven by the biological colonization of the land surface. If early forms of photosynthetic land life selectively weathered continental rock in order to extract nutrients, this would have led to an increase in the flux of biologically available phosphorus to the ocean. We show that recent models for coupled biogeochemical cycles, despite differences in the feedback mechanisms represented, predict this would lead to a rise in atmospheric oxygen concentration, consistent with biological and geochemical evidence. Increased weathering of silicate rocks would also have caused a decline in atmospheric carbon dioxide, which could have been a causal factor in the Neoproterozoic glaciations. A rise in oxygen may have provided a necessary condition for the evolution of animals with hard skeletons seen in the Cambrian explosion. Furthermore, an increase in phosphorus supply to the ocean may have driven an increase in the phosphorus content of marine primary producers. This would have represented an increase in food quality for grazing animals, which have a high phosphorus requirement, and may thus have removed a further limitation on their evolutionary radiation.
DE: 9619 Precambrian
DE: 4805 Biogeochemical cycles (1615)
DE: 4203 Analytical modeling
DE: 0320 Cloud physics and chemistry
DE: 0325 Evolution of the atmosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting