The primary goal of this dissertation is to increase understanding of the so-called Late Devonian mass extinction through the use of stable isotope geochemistry. Despite decades of research, the timing, cause(s), and extent of the events surrounding this devastating interval in Earth history remain poorly understood. One of the best places to study the Devonian period is the Lennard Shelf in the Canning Basin of Western Australia. This region contains extensive, well-preserved exposures of Middle and Upper Devonian (Givetian, Frasnian, and Famennian) carbonate reefal platforms and slopes that are ideal for geochemical analyses. A significant amount of information could be learned about the Late Devonian mass extinction in the Canning Basin if we had a detailed chronostratigraphic framework of platform to basin strata and a better understanding of the paleoenvironmental conditions during the Upper Devonian. This research aims to use stable isotope chemostratigraphy to help build a high resolution chronostratigraphy and examine any environmental changes leading up to and following the F-F boundary that may have contributed to Devonian extinction events in the Canning Basin. This dissertation is divided into two parts; the first concerns my research on the Late Devonian mass extinction while the second is ancillary and documents my astrobiology research rotation. Part 1 contains introductory and concluding remarks as well as three chapters written as scientific manuscripts that have been, or will soon be, submitted for journal publication. The first of these three chapters examines the local and global controls on carbon isotope chemostratigraphy in the Lennard Shelf system to validate the use of secular variations as a chronostratigraphic tool for regional and global correlations. The next chapter provides a detailed, expanded view of the F-F boundary and constrains the pattern of carbon isotope perturbations across said boundary at the intra-zonal scale. The third scientific chapter broadens focus from the F-F to the entirely of the Upper Devonian and presents the first carbon isotope composite curve from Western Australia that is used to test the global nature (timing and extent) of Late Devonian events and examine the relationship between carbon isotope fluctuations, faunal turnover, and changes in the paleoenvironment (sea level, climate, ocean chemistry, paleogeography). Results from Part 1 not only have implications for re-evaluating one of the "Big Five" mass extinctions in the Phanerozoic, but are also relevant to studies in astrobiology and have additional applications in the oil and gas industry. The final chapter of my dissertation, which is in Part 2, concerns interdisciplinary, astrobiology work done during summer quarter, 2014, that was devoted to analyzing the relationship between astronomy and geology circa 1770-1810. This chapter is included in my dissertation as partial fulfillment of my dual-title astrobiology degree.

The first book to review all the evidence concerning both the dinosaur extinctions and all the other major extinctions - of plant, animal, terrestrial, and marine life - in the history of life. All the extinction mechanisms are critically assessed, including meteorite impact, anoxia, and volcanism. - ;Why do mass extinctions occur? The demise of the dinosaurs has been discussed exhaustively, but has never been out into the context of other extinction events. This is the first systematic review of the mass extinctions of all organisms, plant and animal, terrestrial and marine, that have occurred in the history of life. This includes the major crisis 250 million years ago which nearly wiped out all life on Earth. By examining current paleontological, geological, and sedimentological evidence of environmental changes, the cases for explanations based on climate change, marine regressions, asteroid or comet impact, anoxia, and volcanic eruptions are all critically evaluated. -

Based on two decades of research, The Late Devonian Mass Extinction reviews the many theories that have been presented to explain the global mass extinction that struck the earth over 367 million years ago, considering in particular the possibility that the extinction was triggered by multiple impacts of extraterrestrial objects.

Mass extinctions are often associated with multiple environmental perturbations. For example, the Upper and Lower Kellwasser Events (the two pulses of the Frasnian-Famennian mass extinction in the Late Devonian) coincide with both global cooling and ocean anoxia/dysoxia. Assessing the selectivity of extinction-which types of organisms survived versus died-can help constrain which environmental changes were most important as kill mechanisms. Here, selectivity is examined with respect to several factors during the Lower Kellwasser Event. A thick package of siliciclastic sediments was deposited in the Appalachian Foreland Basin during the Late Devonian. Thanks to recent stratigraphic revisions, the Kellwasser Events can be traced along a paleoenvironmental gradient that shallows from west to east in New York and northern Pennsylvania. Previous studies have shown that brachiopod species composition varies significantly along this gradient, and that the Lower Kellwasser Event was the more severe of the two extinctions. The Wiscoy Formation was targeted for this study as it immediately predates the first extinction pulse. We collected bulk samples from numerous localities along the paleoenvironmental gradient and identified 7,933 brachiopod fossils from 21 genera and 26 species. Non-metric multidimensional scaling was used to quantify variation among species in environmental preference; variation in extinction intensity among habitats could indicate that anoxia was a kill mechanism, because oxygen levels likely varied with depth. Brachiopod orders varied in latitudinal distribution in the Devonian, so variation in extinction intensity among orders could implicate cooling as a kill mechanism. We also tested the effects of abundance and body size on probability of extinction. Multiple logistic regression strongly supported global cooling as a major kill mechanism-species belonging to orders prevalent at low latitudes had higher probability of extinction than those belonging to orders common at high latitudes. In contrast, paleoenvironmental preference was not a major predictor of extinction in these data.

The Late Devonian and Permian-Triassic intervals are among the most dynamic episodes of Earth history, marked by large secular changes in continental ecosystems, dramatic fluctuations in ocean oxygenation, major phases of biotic turnover, volcanism, bolide impact events, and rapid fluctuations in stable isotope systems and sea level. This volume highlights contributions from a broad range of geological sub-disciplines currently striving to understand these critical intervals of geologically rapid, global-scale changes. * Provides updated, current models for the mid-Late Devonian and Permian-Triassic mass extinction episodes * Highlights several new analytical approaches for developing quantitative datasets * Takes an integrated approach presenting datasets from a broad range of sub-disciplines

Biodiversity-the genetic variety of life-is an exuberant product of the evolutionary past, a vast human-supportive resource (aesthetic, intellectual, and material) of the present, and a rich legacy to cherish and preserve for the future. Two urgent challenges, and opportunities, for 21st-century science are to gain deeper insights into the evolutionary processes that foster biotic diversity, and to translate that understanding into workable solutions for the regional and global crises that biodiversity currently faces. A grasp of evolutionary principles and processes is important in other societal arenas as well, such as education, medicine, sociology, and other applied fields including agriculture, pharmacology, and biotechnology. The ramifications of evolutionary thought also extend into learned realms traditionally reserved for philosophy and religion. The central goal of the In the Light of Evolution (ILE) series is to promote the evolutionary sciences through state-of-the-art colloquia-in the series of Arthur M. Sackler colloquia sponsored by the National Academy of Sciences-and their published proceedings. Each installment explores evolutionary perspectives on a particular biological topic that is scientifically intriguing but also has special relevance to contemporary societal issues or challenges. This tenth and final edition of the In the Light of Evolution series focuses on recent developments in phylogeographic research and their relevance to past accomplishments and future research directions.