Claimed Periodicity of Mass Extinctions
In 1984, paleontologists David Raup and Jack Sepkoski published a paper claiming that they had identified a statistical periodicity in extinction rates over the last 250 million years using various forms of time series analysis. They focused on the extinction intensity of fossil families of marine vertebrates, invertebrates, and protozoans, identifying 12 extinction events over the time period in question. The average time interval between extinction events was determined as 26 million years. At the time, two of the identified extinction events (Cretaceous-Paleogene and Late Eocene) could be shown to coincide with large impact events. Although Raup and Sepkoski could not identify the cause of their supposed periodicity, they suggested a possible non-terrestrial connection. The challenge to propose a mechanism was quickly addressed by several teams of astronomers.
In 2010, Melott & Bambach re-examined the fossil data, including the now-improved dating, and using a second independent database in addition to that Raup & Sepkoski had used. They found evidence for a signal showing an excess extinction rate with a 27-million-year periodicity, now going back 500 million years, and at a much higher statistical significance than in the older work. The change from 26 to 27 million years is expected based on a 3% "stretch" in the geological timescale since the 1980s.
Read more about this topic: Nemesis (hypothetical Star)
Famous quotes containing the words claimed and/or mass:
“No actual skeptic, so far as I know, has claimed to disbelieve in an objective world. Skepticism is not a denial of belief, but rather a denial of rational grounds for belief.”
—William Pepperell Montague (18421910)
“Compare the history of the novel to that of rock n roll. Both started out a minority taste, became a mass taste, and then splintered into several subgenres. Both have been the typical cultural expressions of classes and epochs. Both started out aggressively fighting for their share of attention, novels attacking the drama, the tract, and the poem, rock attacking jazz and pop and rolling over classical music.”
—W. T. Lhamon, U.S. educator, critic. Material Differences, Deliberate Speed: The Origins of a Cultural Style in the American 1950s, Smithsonian (1990)