National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: ABSTRACT

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Suggested Citation:"ABSTRACT." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
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Page 47

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GLOBAL CHANGE LEADING TO BIODIVERSITY CRISIS IN A GREENHOUSE WORLD: THE CENOMANIAN-TURONIAN 47 (CRETACEOUS) MASS EXTINCTION 3 Global Change Leading to Biodiversity Crisis in a Greenhouse World: The Cenomanian-Turonian (Cretaceous) Mass Extinction Earle G. Kauffman University of Colorado ABSTRACT The Cenomanian-Turonian (C-T) mass extinction occurred during a peak global greenhouse interval, with eustatic sea- level elevated nearly 300 m above present stand; atmospheric CO2 at least four times present levels; and global warm, more equable climates reflecting low thermal gradients from pole to equator, and from the top to the bottom of world oceans. Despite development of an oceanic anoxic event (OAE II), marine diversity was at a Cretaceous high just prior to the extinction interval; many lineages had evolved narrow adaptive ranges over millions of years under greenhouse conditions. Marine biotas were thus extinction prone. Tropical reef ecosystems experienced widespread extinction beginning near the early-middle Cenomanian boundary; major lower Cretaceous lineages of reef-building rudistid bivalves were largely extinct by middle-late Cenomanian time. Within 520,000 yr of the C-T boundary, nontropical late Cenomanian biotas experienced 45-75% species extinction, depending on the group, through a series of discrete, ecologically graded, short-term events, or steps, beginning with subtropical and warm temperate stenotopic biotas, and terminating with more broadly adapted cool temperate biotas. These extinction events were closely linked or coeval with abrupt, large-scale perturbations in the ocean- climate system, as evidenced by major fluctuations in trace elements (including Ir), stable isotopes, and organic carbon values; the rate and magnitude of these chemical and thermal perturbations progressively exceeded the adaptive ranges of various components of the marine ecosystem as the effects of late Cenomanian environmental perturbations became compounded through time. Two possible catalysts for these abrupt environmental changes are (1) expansion of the oceanic oxygen minima zone(s) to intersect both the deep ocean floor, and deeper continental shelf and epicontinental sea habitats, initiating trace element advection and chemical stirring of the oceans; and (2) oceanic impacts of meteorites and/or comets as part of the Cenomanian impact shower. Evidence is presented for both hypotheses, and a multicausal explanation for C-T mass extinction is

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What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

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