Walnut stones, fossil

Even more surprising is the presence of the diunsaturated acid 18 2 in all coal samples studied. The presence of diunsaturated acids is indeed highly unusual because of their inherent instability under geological conditions. Itihara et al. (42) have reported the presence of 18 2 in a fossil walnut stone of estimated age one million years (Pleistocene), but this appears to be the first report of a diunsaturated acid in a sediment or coal from the Eocene epoch or the Permian period. 

Itihara, Yuuko Inoue, M. Nirei, H. Lipids in Fossil Walnut Stones , J. 

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