Karl W. Flessa, 1990. "The “facts” of mass extinctions", Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality, Virgil L. Sharpton, Peter D. Ward
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The years since Snowbird I have seen an explosive growth of research on the patterns, rates, causes, and consequences of extinction. The fossil record of evolution is better known, new stratigraphic sections have been scrutinized in great detail, and additional markers of environmental change have been discovered in the rock record.
Three contrasting interpretations of the fossil record of extinction are possible: catastrophic extinction, gradual extinction, and stepwise extinction. Each interpretation is supported by some of the evidence.
However flawed, the fossil record is the only record we have of natural extinction. Compilations from the primary literature provide insight on the magnitude, breadth, and periodicity of mass extinctions. Outcrop-based studies have the potential to resolve controversies over the precise rate and pattern of mass extinctions. Unfortunately, a literal reading of the fossil record is made difficult by the manner in which fossils occur in strata and by the way in which fossils are collected and studied.