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Anther occurred when the Cretaceous period became the Tertiary about 65 million years ago, when 75 percent of species disappeared. This article is about the first mass extinction at the end of the Ordovician geological period 440 million years ago, when about 86 percent of species were killed.
Kirk Janowiak, Eclectic, educated, and loves to teach. Views. There is only one cause for mass extinctions and that is a major or equally massive change in the environment a large scale. Any wide-scale event or series of events that can alter the regional or global climate and/or environment over a large area can, thus, trigger a mass extinction. Such events might include: