The Roles of Bad Luck and Periodicity in Species Extinctions
To the extent that bad luck, and periodically recurring natural causes, explain species extinctions, the role of humans in causing extinctions may be less than is sometimes assumed.
(p. A21) Dr. Raup challenged the conventional view that changes in diversity within major groups of creatures were continuous and protracted, and advanced the theory that such changes can be effected by random events.
And he questioned the accepted notion that biodiversity -- that is, the number of extant species -- has vastly increased over the past 500 million years, pointing out, among other things, that because newer fossils embedded in newer rock are easier to find than older fossils in older rock, it is possible that we simply have not uncovered the evidence of many older species whose existence would undermine the theory. His conclusion, that the data of the fossil record does not allow the unambiguous presumption that biodiversity has increased, has profound implications.
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Dr. Raup's most famous contribution to the field may have been the revelation in 1983, after a six-year study of marine organisms he conducted with J. John Sepkoski Jr., that over the last 250 million years, extinctions of species spiked at regular intervals of about 26 million years.
Extinction periodicity, as it is known, enlivened the study of huge volcanic eruptions and of changes in the earth's magnetic field that may have coincided with periods of mass extinction. It has also given rise to numerous theories regarding the history of life, including that the evolution of myriad species has been interrupted by nonterrestrial agents from the solar system or the galaxy.
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"Much of our good feeling about planet Earth stems from a certainty that life has existed without interruption for three and a half billion years," he wrote. "We have been taught, as well, that most changes in the natural world are slow and gradual. Species evolve in tiny steps over eons; erosion and weathering change our landscape but at an almost immeasurably slow pace."
He continued: "Is all this true or merely a fairy tale to comfort us? Is there more to it? I think there is. Almost all species in the past failed. If they died out gradually and quietly and if they deserved to die because of some inferiority, then our good feelings about earth can remain intact. But if they died violently and without having done anything wrong, then our planet may not be such a safe place."
For the full obituary, see:
(Note: ellipses added.)
(Note: the online version of the obituary has the date JULY 15, 2015 and has the title "David M. Raup, Who Transformed Field of Paleontology, Dies at 82.")