This project address an important, and unresolved question in Earth evolution, i.e. did the eruption of the Siberian Large Igneous Province (LIP) a.k.a. Siberian Traps cause the Permo-Triassic extinction? In reality there are two questions at the heart of this proposal; what causes flood basalts and do flood basalts cause extinctions? These questions have been the subject of active research for several decades. One of the unique aspects of this project is that both are addressed simultaneously by an international team of experts whose goal is to gain an in-depth understanding of this LIP from its origin to both short-and long-term effects on Earth systems. The PIs will use a large suite of techniques: geochemistry, geothermometry, paleomagnetics, seismology, geodynamics, paleontology, and climate modeling to achieve their goal. Specifically, the PIs will:
> create high-precision eruption time scales for the entire volcanic succession, thus obtaining flux rates; > quantify the volatile loads of the igneous rocks including lavas, intrusives, and in particular the voluminous tuffs; > quantify volatile release from country rocks; > begin to map the crustal and upper-mantle structure beneath the region using existing seismic data and geodynamical modeling; > study the climatic consequences of sulfur injection and buildup of atmospheric carbon dioxide; and > continue detailed studies of the end-Permian extinction, using paleontology, stable isotope geochemistry, and geochronology.
Broader Impacts:
The PI team consists of scientists from 7 different countries. A central repository will be created for samples obtained under this project. Information will be maintained on the web and material made available to other scientists. A documentary film producer associated with the National Geographic Corporation will be in the field with the PIs gathering footage for a film about the project. Additional coverage is will be provided through the American Museum of Natural History?s Science Bulletins, short films about current research that are shown at the AMNH and distributed to over 40 science centers and museums around the world.
In this project, we studied the potential causes of the mass extinction event that occurred at the end of the Permian Period, 252 million years ago, through an analysis of the pattern of extinction and survival across marine animal genera and through chemical analysis of limestone rocks deposited before, during, and after the mass extinction event. Our major finding from the analysis of extinction selectivity was that the end-Permian mass extinction event preferentially eliminated marine animals with massive calcium carbonate shells relative to soft-tissue mass, especially those lacking active respiratory and circulatory systems that aid in gas exchange with the environment (i.e., respiration). Geographic range had only a weak correlation with extinction risk. In constrast, extinctino during the preceding geological stages was not selective with respect to the presence or absence of a calcium carbonate shell or gills and circulatory system but was highly selective with respect to geographic range. These findings suggest that the end-Permian mass extinction resulted from a rapid interval of global environmental change. Our major finding from the chemical analysis of limestone rocks was a change in the calcium isotope composition (ratio of the calcium-44 isotope to the calcium-40 isotope) of the rocks across the main extinction horizon. This change in the calcium isotope ratio is predicted by an ocean acidification scenario but not by simple die-off of marine phytoplankton or by upwelling of alkaline deep waters. The calcium isotope data can further be used to estimate the amount and source of carbon release required to explain an associated change in the carbon isotope composition (ratio of the carbon-13 isotope to the carbon-12 isotope) of the same limestones. This analysis suggests that Siberian Traps volcanism was a likely source of the carbon through volatilization of limestones and coals in the Siberian continental crust and that methane clathrates were an unlikely source of the carbon. The mass of carbon required to account for this excursion is between 10,000 and 50,000 gigatons. This project provided training and learning opportunities for numerous individuals. Five graduate students and one post-doctoral fellow participated directly in the research and were mentored through weekly meetings with the PI. In addition, these individuals obtained interdisciplinary training through project meetings spanning the disciplines of paleontology, geochemistry, geochronology, petrology, and climate modeling. To date, we have produced 12 published journal articles and made 51 conference presentations based on this research. The PI has presented the results of this work to other Earth scientists through departmental lectures at numerous universities, including Stanford, UC Berkeley, Princeton, Syracuse University, and MIT. A high school teacher and six high school students also participated in research through summer internships at Stanford University, and five of the high school students presented results of the summer project at the American Geophysical Union annual meeting in San Francisco. Our research was also featured in the New York Times and is currently being incorporated into a documentary film planned to air as part of the NOVA series. The growing evidence that the end-Permian mass extinction was driven by an episode of ocean acidification, as supported by our work on extinction selectivity and calcium isotope geochemistry, will likely increase the awareness in the conservation biology and global change communities of the value of extinction events in the fossil record as ancient analogs for the twenty-first century. We anticipate that our work will prompt researchers in these fields to consider deep time crises more seriously as sources of useful information when predicting potential outcomes from anticipated global change. More broadly, understanding how our world came to look the way that it does is one of the deepest and most fundamental human desires. The end-Permian mass extinction was among the two or three most important events in the history of animal life that shaped the world we live in today. The improved understanding of this event developed through this project will help all curious people understand more accurately why the biological world we inhabit looks the way that it does and comprehend more clearly the processes that can disturb it.
