Cycles in Fossil Biodiversity

There have long been discussions of apparent periodicity in the fossil record, but in 2004 there appeared a study which showed high statistical significance for a 62 million year periodicity going back about 500 million years. We have re-examined and verified this result, which is dominated by low-frequency components, and among these the 62 My cycle strongly dominates.

Since that time, our time series analysis of fossil biodiversity has greatly expanded. We have examined two additional independent compendia of fossil biodiversity history, as well as the timing of mass extinctions, in the first and second of a three-paper series. A simple visual summary of the main idea can be seen below.

As you can see, the best-fit to the dominant peak agrees very well in both period and phase between the three independent analyses. Second, a majority of the mass extinctions identified by Bambach (2006) lie on the downside of the cycles, suggesting that they have a relationship as well to the timing of these events. The significance of these 4 independent statistical tests varies from p-values of 0.001 to 0.05, depending upon the test and precise details of the method. We therefore regard the reality of these cycles as a given, and are now engaged in trying to understand what may be causing them.

One possibility is rooted in the timing coincidence: The vertical oscillation of our Sun in the Galaxy is nearly in phase with this biodiversity cycle. From this, Medevedev and Melott have constructed a candidate mechanism based on a major variation in the cosmic ray flux on the Earth, linked here.

In the second and the third we offer causal clues. Melott, Bambach, Petersen, and McArthur have undertaken a series of analyses to determine what might be causing this periodicity. They find a series of clues:

The most natural explanation is periodic uplift, if one can account for rather precise timing, perhaps from mantle plumes. Is this a clue from biodiversity to the internal dynamics of our planet --a beating heart? The signal would seem to require synchronous changes in the uplift of continents, rather than changes in sea level.

We continue to actively pursue research on both the dynamics of the diversity signal and the investigation of possible causes.

Home again