Permo-Triassic extinction

Wignall P. B. and Hallam A. (1993) Griesbachian (Early Triassic) palaeoenvironmental changes in the Salt Range, Pakistan and southeast China and their bearing on the Permo-Triassic extinction. Palaeogeogr. Palaeoclimat. Palaeoecol. 102, 215-237. 

The end of the Permian Period is defined by the extinction of about 90% of all life forms that existed on the Earth at that time. This catastrophe was even more severe than the extinction event that defines the end of the Cretaceous Period which resulted from the profound environmental disturbance caused by the impact of an asteroid at Chicxulub on the Yucatan Peninsula of Mexico. The cause of the Permo-Triassic extinction could have been a dramatic fluctuation of the global climate, or of sealevel, or the impact of an asteroid or comet, or severe volcanic activity, or all of the above. 

Retallack et al. (1998) briefly reviewed the literature concerning the causes of the Permo-Triassic extinction event as an introduction to their own study to determine whether boundary clays at Graphite Peak between the Buckley and Fremouw formations contain shocked quartz and anomalously high concentrations of iridium of meteoritic origin. Although they found shocked... 

In a related study, Basu et al. (2003) reported finding meteorite fragments and metalUc grains in rock samples from Graphite Peak. However, in the absence of an impact crater and other geomorphic evidence that is characteristic of impact events, the search for the causes of the Permo-Triassic extinction event continues. 

Pitrat, C.W. (1973) Vertebrates and Permo-Triassic extinction. Palaeogeography, Palaeoclimatology, Palaeoecology, 14 249-264. 

Berner R. A. (2002) Examination of hypotheses for the Permo-Triassic boundary extinction by carbon cycle modeling. Proc. Natl. Acad. Sci. 99, 4172-4177. 

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