酸雨和臭氧枯竭造成古代物种大灭绝

Around 250 million years ago, at the end of the Permian period, there was a mass extinction¹ so severe that it remains² the most traumatic（创伤的） known species die-off in Earth's history. Some researchers have suggested that this extinction was triggered by contemporaneous（同时期的） volcanic³ eruptions⁴ in Siberia. New results from a team including Director of Carnegie's Department of Terrestrial Magnetism⁵ Linda Elkins-Tanton show that the atmospheric⁶ effects of these eruptions could have been devastating⁷. Their work is published in Geology. The mass extinction included the sudden loss of more than 90 percent of marine⁸ species and more than 70 percent of terrestrial species and set the stage for the rise of the dinosaurs⁹. The fossil record suggests that ecological¹⁰ diversity did not fully¹¹ recover until several million years after the main pulse of the extinction.   One leading candidate for the cause of this event is gas released from a large swath of volcanic rock in Russia called the Siberian Traps. Using advanced 3-D modeling techniques, the team, led by Benjamin Black of the Massachusetts Institute of Technology, was able to predict the impacts of gas released from the Siberian Traps on the end-Permian atmosphere.   Their results indicate that volcanic releases of both carbon dioxide (CO2) and sulfur¹² dioxide (SO2) could have created highly acidic rain, potentially leaching¹³ the soil of nutrients¹⁴ and damaging plants and other vulnerable terrestrial（陆生的） organisms. Releases of halogen-bearing compounds such as methyl chloride（氯甲烷） could also have resulted in global ozone¹⁵ collapse¹⁶.   The volcanic activity was likely episodic, producing pulses of acid rain and ozone depletion¹⁷. The team concluded that the resulting drastic fluctuations¹⁸ in pH and ultraviolet radiation, combined with an overall temperature increase from greenhouse gas emissions¹⁹, could have contributed to the end-Permian mass extinction on land.   The team also included Jean-François Lamarque, Christine Shields, and Jeffrey Kiehl of the National Center for Atmospheric Research.