Date:9/25/2008

m to track the rise of atmospheric oxygen. A rather new method is the measurement of the isotopic composition of molybdenum in sediments. Molybdenum isotope ratios act as fingerprints to identify changes in the oxygen content of the oceans through time -- i.e., the clearest and most direct geochemical trace of biological activity (life) through Earth's history. In order to quantify paleoceanic change, we need a fundamental understanding of the processes of the global molybdenum cycle. Neubert et al. has carried out a detailed study of surface sediment samples from the Black Sea from different water depths. The Black Sea is an archetype of recent marine anoxic (oxygen free) environments. The author's isotope results confirm that molybdenum solubility is strongly related to the amount of dissolved sulphide in the water column. Further, molybdenum isotopes indicate that there is a well-defined threshold value of sulfide concentration above which the scavenging from molybdenum from the water column is complete. This determination of the threshold value provides a fundamental parameter for future studies of the oxygen history in the geological past by means of molybdenum isotopes.

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Miocene tectonics and climate forcing of biodiversity, western United States
Matthew Kohn and Theodore Fremd, Department of Geosciences, Boise State University, 1910 University Dr., Boise, Idaho 83725, USA. Pages 783-786. NSF funding received.

Kohn and Fremd have found that the diversity patterns of carnivores and hoofed mammals in the western United States over the past 30 million years show changes related to crustal extension, global cooling, and increased climate seasonality. Increased diversities at 17 to 17.5 million years ago reflect increased topographic variability that resulted from extension. Decreased diversities circa 11 million years ago and the rapid increase in warm climate (C4) grasses at 7-8 million years ago reflect climate teleconn
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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