BOULDER, Colo. - Highlights from the Geological Society of America's November issue of GEOLOGY include a new "curveball" of evidence to the Snowball Earth hypothesis, findings about magma coming from the Earth's mantle in the Arctic Gakkel Ridge eruption, details about the discovery of Canada's oldest shelly fossils, decreased solar forcing as a trigger for a cooling event during the early Holocene, vertebrate extinctions during the Permian-Triassic as found in South Africa's Karoo Basin, and nutrient-triggered bio-erosion in the Palliser Formation of western Canada. Summaries of these articles and others, as well as a summary of the science article from the December issue of GSA TODAY, are provided below. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY or GSA TODAY in stories published. Contact Ann Cairns at acairns@geosociety.org for copies of articles and for additional information or other assistance.

Carbon isotopic composition of Neoproterozoic glacial carbonates as a test of paleoceanographic models for Snowball Earth phenomena.
Martin J. Kennedy et al. Department of Earth Science, University of California, Riverside Riverside, CA 92521-0423, USA. Pages 1135-1138.

The Snowball Earth hypothesis of P.F. Hoffman and colleagues proposes that during times of especially widespread glaciation ca. 600-750 Ma, the surface ocean became completely covered with ice, resulting in the mass extinction of marine life. The prospect that such events occurred more than once is intriguing for its implications about Earth's climate system and the possibility that snowball conditions acted as evolutionary bottlenecks, preventing the appearance of complex organisms. The authors test this idea by measuring the ratio of the carbon isotopes 13C and 12C within carbonate sediments that precipitated during ice ages in the
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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
3-Dec-2001

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