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OVERVIEW AND RECOMMENDATIONS 1 Overview and Recommendations OVERVIEW The geologic record provides a unique, long-term history of changes in the global environment and of the impact of these changes on life. From the fact that organisms are intimately related to their environment, we can infer that environmental changes of the past have molded the history of life. The geologic record contains the paleontological evidence that confirms this inference for a wide range of temporal and spatial scales. Study of this record is providing a framework for evaluating the impact of present and future global change on the biosphereâa framework that is urgently needed for the formulation of public policy. What can be expected to happen to biotic communities when climatic zones shift or habitats shrink? As trends of global change progress, what thresholds may trigger sudden shifts between environmental states or cause catastrophic destruction of life? Lessons of the past will serve us well as we confront the future. The geologic record reveals how particular kinds of environmental change have caused species to migrate, become extinct, or give rise to new species. More generally, it shows that many kinds of species and ecosystems are naturally fragile, and therefore transient, whereas other kinds are inherently more stable. Many advances in the understanding of ancient ecosystems are interdisciplinary in nature. Accurate plate tectonic reconstructions are essential for the evaluation of circulation patterns for ancient atmospheres and oceans. Geochemical data help us to understand ancient atmospheric and oceanic compositions, as well as climates. Functional morphology and studies of fossil preservation reveal modes of life of extinct species, and knowledge of the ecological requirements of fossilized organisms complements sedimentological analyses in the reconstruction of ancient environments. Fossil plants are among the most important indicators of ancient terrestrial climates, and studies of microfossil assemblages and stable isotopes are critical for reconstructing the three-dimensional structure of
