The End Permian Mass Extinction

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greatest extinction (McKinney, 1987). The end of the Permian and beginning of the Triassic periods marked the single greatest extinction event the world has ever faced.

Timing of the Extinction
There are many questions regarding the timing of the extinction at the end of the Permian. One of the main questions was the even a catastrophy or gradual. There is evidence for both senarios. Some of the evidence supports an ectraterrestrial even such as a metior. Other evidence supports the theory of the ocean and terrestrial environments slowly changing.

Geochemical evidence
The research done by Xu Dao-Yi and Yan Zheng (1993)gives evidence for an extraterristrial event. They made a table which showed the distribution of carbon 13, iridium, and microspherules across the P/T (Permian and Triassic) border. The section was over a thickness of 35 cm. They found a sudden depletion in C-13 falling from a value near zero to a minimum of less than -6% in some samples. Similar patterns of C-13 have been observed in more than five P/T sections in China. Some other scientists like Baud et al (1989) argue that what could have caused this anomaly is the result of a depositional hiatus or erosional disconformity. Xu and Yan argue that there is no evidence for a significant hiatus and that Baud et al. Even made a mistake in the timing of their rock layers. "If the PTB [Permian Triassic boundary] is considered a catastropic event, a short-time hiatus should be expected and is in fact a reasonable consequence of a catastrophic event" (by Xu Dao-Yi and Yan Zheng, 1993). But what is the significance of C-13 being associated with catastrophic events? Hsu et al. (1982) said that they suggested that carbon isotope anomalies are related to microplankton productivity. We will touch again on this later in the paper. Therefore, the sudden C-13 change may indicate the exact stratigraphic position of the mass killing event at the PTB. Analysis of iridium (Xu Dao-...