Huge global fires marked the end of the Cretaceous period 65 million years ago, say researchers in the US.
Linda Ivany and Ross Salawitch of Harvard University analysed carbon isotopes in the layer which marks the boundary between the Cretaceous and Tertiary periods. They concluded that at the time of the extinction of the dinosaurs about 25 per cent of the Earth's biomass above ground burnt (Geology, vol 21, p 487). This dovetails with a recent finding of Wendy Wolbach and Ed Anders of the University of Chicago, who discovered soot at the boundary.
Ivany and Salawitch used the fact that when plants photosynthesise they use carbon-12, the common isotope of carbon, more efficiently than the rare isotope, carbon-13. The 'extra' carbon-13 remains in the carbon dioxide in the atmosphere, and is incorporated into the shells of organisms near the surface of the ocean. So measuring the level of carbon-13 ...
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