Only geohistorical data—the organic remains, biogeochemical signals, and associated sediments of the geological record—can provide a time perspective sufficiently long to establish the full range of natural variability of complex biological systems, and to discriminate natural perturbations in such systems from those induced or magnified by humans. Such data are crucial for acquiring the necessary long-term perspective on modern systems. Information from past environmental states, both like and unlike those of the present day, provide the empirical framework needed to discover the general principles of biosphere behavior necessary to predict future change and inform policy managers about the global environment.



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