Deep-time biotic crisis


     Permian-Triassic transition at 252 million years ago is one of the critical periods in Earth history, featured by the most severe biotic mass extinction in Phanerozoic and the protracted recovery, in association with abrupt changes of paleoclimate and paleoenvironment. Three papers published in Science during 2000-2004 stated extraterrestrial impact caused the most sever biotic crisis, and triggered a high debate on causes of the mass extinction. By focusing on the geolipids and some other biogeochemical records, the MGP is among the first worldwide to propose the occurrence of at least two episodic changes of a series of environmental conditions in Earth surface system across the Permian-Triassic boundary, including the microbial expansion, carbon cycling, enhanced terrestrial erosion and wild fire. The pattern of two episodes in paleoenvironmental changes was found to couple with a two-episodic mass extinction identified both at individual sections and multiple sections at a broad region in South China. The pattern of two episodes he proposed has been documented in a series of faunal records including brachiopods, higher plants, foraminifers, trace fossils, and was recognized as ‘Extinction theory: a double episode’ published in Nature China. These records identified by the MGP demonstrate that single extraterrestrial impact could not be the main causes of the biotic crisis. Later on, he measured the microbial sediments in over 10 sections and volcanic sediments in 27 sections in South China, and found that the two different sediments show a strong spatial relationship; the sites with relatively extensive volcanisms shown by the volcanic sediments are featured by the relatively long time of microbial expansion due to the enhanced input of volcanic nutrients. Their spatial relationship is a consequence of their cause-effect relationship. Consequently, these data suggest that volcanisms in South China might play an important role in triggering the episodic changes in Earth surface system, including the faunal mass extinction in this region.