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September Geology and GSA Today media highlights
Date:8/28/2007

erules, tektites, and accretionary lapilli demonstrate that the extraterrestrial body was a meteorite and not a comet, as previously proposed. The Sudbury event was larger than those responsible for later major extinction events, and may prove important in the evolution of early life on Earth.


Desert speleothems reveal climatic window for African exodus of early modern humans
Anton Vaks, Hebrew University, Institute of Earth Sciences, Edmond Safra Givat Ram Campus, Jerusalem 91904, Israel; et al. pages 831-834.

The African origin of early modern humans 200,000150,000 years ago is now well documented, with archaeological data suggesting that a major migration from tropical east Africa to the Levant took place between 130,000 and 100,000 years ago via the presently hyper-arid Saharan-Arabian desert. This migration was dependent on the occurrence of wetter climate in the region. Whereas there is good evidence that the southern and central Saharan-Arabian desert experienced increased monsoon precipitation during this period, no unequivocal evidence has been found for a corresponding rainfall increase in the northern part of the migration corridor, including the Sinai-Negev land bridge between Africa and Asia. Passage through this bottleneck region would have been dependent on the development of suitable climate conditions. Vaks et al. present a reconstruction of paleoclimate in the Negev Desert based on absolute uranium series dating of carbonate cave deposits (speleothems). Speleothems only form when rainwater enters the groundwater system and vegetation grows above a cave. Today the climate in the Negev Desert is very arid and speleothems do not form, but their presence in a number of caves clearly indicates that conditions were wetter in the past. Vaks et al. dated 33 speleothem samples from five caves in the central and southern Negev Desert. The ages of these speleothems show that the last main period of increased rainfall occurre
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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
Source:Eurekalert

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