[LINK] "Periodicity on the Quick"

[rfmcdonald]

Continuing the theme of Nemesis, Will Baird doesn't think much of the idea of regular mass extinctions every 27 million years. It turns out that they caught my attention; others', too.

Periodicity came out of a paper done by Raup and Sepkoski back in 1984 based on a database of marine fossils that suggested that there might be a regular pattern to the mass extinctions. They felt they had uncovered a pattern of regular mass extinctions at 26 million years. This, in turn, inspired the idea of Nemesis, a dwarf companion to our sun. There was a hunt for Nemesis, which turned up zilch. Others have suggested that it is actually the sun's orbit around the center of the galaxy and the movement above and below the galactic arms that would cause the periodic signal. The most recent paper that refutes that there could not be a companion star such as Nemesis. It also casts doubt on the galactic orbit having anything to do with the extinctions. They still uncover a 27 million year repeating pattern for the extinctions.

Some of the popular press has stated that the general consensus amongst extinction researchers is that periodicity is real. Unfortunately, that's incorrect. There isn't a general consensus that agrees on this. On the contrary, it looks as though most researchers, other than a few (mostly physics and astronomy types), have rejected the idea. The idea, while perhaps not fringe, is definitely not in the mainstream.

Part of the reason for that is that there are at least two different killers for mass extinctions: impacts (KT Extinction) and vulcanism (Permian-Triassic and Late Triassic Extinctions). There seems to be a third, too: radically cooling (Eocene). Making these rather different extinction mechanisms follow a regular clock seems implausible at best.

A quick comparison of predicted mass extinctions versus actual ones leaves him unsatisfied. The causes of the mass extinctions are so different: can a single extraterrestrial body like Nemesis really be responsible?

The whole thing doesn't really hold water for me. Period ending extinctions are the best fit...but...the causes have zilch in common! KT: Impact. TJ: Vulcanism. Ordovician: Glaciation! The patterns of the extinctions are also different from one another. How an asteroid, a volcano, and a glaciation can have the same cause...well...that stretches credibility a bit.