Science at the Limit (Part 1)

Here is an amazing piece of recent scientific analysis. What I find so striking about this is the untold number of years that must have gone into accumulating the dataset that is examined here.

Richard A. Muller, a physicist at Lawrence Berkeley National Laboratory, and Robert A. Rohde, a graduate student in physics at the University of California, Berkeley presented a paper in Nature called Cycles in Fossil Diversity (PDF). In it, they subject the vast amount of accumulated extinction data to Fourier analysis to determine if there are any detectable cycles in the archeological record.

As can be seen is this graph based on their report, two cycles—the most pronounced at 62 millions years, another smaller one at 140 million years—clearly stand out:

In the latest edition of Brian Hayes’ always excellent column in American Scientist, he takes Muller and Rohde’s original dataset and subjects it to his own analysis. He goes into a bit more detail on some of the assumptions that had been made and ultimately comes up with similar results.

Muller and Rohde speculate that while the cycles may reflect either the integrity of the fossil record itself, or some unknown long-term biological process, it is worth speculating on potential geophysical causes. They consider several different possibilities, all of which have been brought up in the past:

• Passage of the solar system through the arms of the galaxy on 140-million year cycles.
• Oscillation of the solar system through the galactic plane.
• Mantle plume cycles that affect vulcanism.
• Long-period solar cycles that affect weather patterns.
• Orbital perturbations caused by planetary alignments.
• An undetected solar companion star that disturbs the Oort cloud.
• A large, planet-sized Kniuper belt object that disturbs the Oort cloud.

However none of these can definitively be tied to the extinction cycles themselves.