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Periodicities in Biodiversity and Possible

Causal Factors

Primary collaborators: Richard Bambach, Bruce Lieberman

Adrian L. Melott Dept. Physics & Astronomy, University of Kansas

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Is one frequency dominant? If so, this is evidence of a repetitive pattern.

Patients with atrial fibrulation as shown above tend to show a repetitive pattern of pulses. This can be measured by the power spectrum, shown below. This is the squared amplitude of waves present as a function of their frequency. It tells how much variance comes from each frequency.

(In sound or electromagnetic waves squared amplitude is energy density).

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Rohde & Mueller Analysis: a 62 Myr Biodiversity Cycle?

Robert A. Rohde and Richard A. MullerNature 434, 208-210 (10 March 2005)

Uses Sepkoski (2002) data with Gradstein et al. (2004) dates

T = 62 ± 3 MyP = 0.01 (Monte Carlo)

Cross-spectra tell us when two signals possess the same periodic fluctuation, and can tell us whether the fluctuations are in phase or not. In this case, all three data sets possess the same important periodic fluctuation, around a period of 62 Myr with the same phase within 1 or 2 Myr.

Sepkoski X PBDB Sepkoski X FR2 marine FR2 marine X PBDB

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Causal Clue I: Solar Z(t) and 62 Myr BD component: one motivating “coincidence”

Causal Clue II: number of sedimentary rock packages

We see here (from Melott & Bambach 2011 PB 37,383) the power spectrum of (area/continuity weighted) carbonate rock package data from Peters (2008), and its cross-spectrum with the Sepkoski biodiversity data, all detrended. Note the zero point of the y-axis on the right. Most of the positive correlation between the two results is from power around 60 Myr. We have found a similar but weaker signal in the siliciclastic package data.

Causal Clue III: Strontium Isotope Ratios87Sr/86Sr isotopic ratios show a strong peak at 59 ± 3 Myr (not shown). Detrended and divided by their own standard deviation, the Sr isotope fit (dashed) and short-lived faunal diversity (solid) are anticorrelated at about -0.5 (below). As seen in the cross-spectrum (right), most of this is driven by a fluctuation in the 60 Myr range, a strong negative peak that has the two cycles almost perfectly out of phase. This is probably the most natural explanation: continental uplift increases granitic erosion and deprives organisms of continental shelf habitat, terminating those that are sensitive to such a stress. But why is it periodic?

Is it uplift? Is it periodic from Mantle Plumes?

• Uplift will reduce the amount of sedimentary packages (commonly found from former epicontential regions). Mass extinctions preferentially happen when this is declining.

• Uplift will increase the erosion rate of granitic rock by exposing it to increased precipitation and freeze-thaw cycles, increasng 87Sr/86Sr.

• Uplift will provide a stress on marine organisms which may transform ordinary extinction events into severe, mass extinction events…flu?

• Mantle plumes periodic?? Suggested by Melott, Bambach, Petersen, and McArthur, J. Geology 120, 217 (2012); Rampino and Prokoph, EOS 94, 113 (2013)

• Some accounts of numerical simulation of mantle plumes have claimed periodic behavior—but with very little analysis to describe it. More work needs to be done.

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Exinction Intensity Over Time

Raup and Sepkoski 1984 PNAS 81:801

Used Families. Tension between noise, incompleteness and sensitivity. Used older dating methods—inaccurate before 250 Mya. A new look?

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Our Latest Look: Use Sepkoski and PBDB extinction rates, with 2012 Geological Time

Scale back to 470 MaWe see power spectra of the Sepkoski and PBDB fractional extinction rates (genus extinction per genus per interval). There is a feature at 27 Myr, p=0.02. The Raup and Sepkoski result emerges with higher significance, in both data sets, over nearly the entire Phanerozoic.

With the new timescale and choices of interval, there are no longer any significant spectral features in the distribution of interval lengths.

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An aside about extinction: Extinction fraction against (Sep) interval length is basically a scatter plot: Least squares slope close to zero, r2 close to zero. There is no evidence here for any significant continuous component to extinction!

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A busy, busy plot. Bambach identifies 6 new Phanerozoic mass extinctions, to bring the total to 25, 19 in the last 470 Myr. 16 of 19 fall within the declining half of the 62 Myr cycle (grey bands) p=0.002. 10 of 19 fall within 3 Myr of peaks of the 27 Myr extinction cycle (vertical dotted lines, filled circles, p=0.004.

The data seem to be most consistent with both periods contributing to the cycles of extinction, with the 62 Myr cycle having greater net effect on biodiversity. They appear to provide a kind of background “stress” that promotes ordinary extinctions into mass extinctions.

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Resources

• Melott & Bambach (2010) “Nemesis Reconsidered”, Monthly Notices of the Royal Astronomical Society Letters 407, L99-L102.

• Melott, Bambach, Petersen, & McArthur (2012) “A ~60 Myr periodicity is common to marine-87Sr/86Sr, fossil biodiversity, and large-scale sedimentation: what does the periodicity reflect?” Journal of Geology, 120, 217-226 (2012)--and references therein.

• Melott & Bambach “Analysis of periodicity of extinction using the 2012 geological time scale” Paleobiology, in press.

http://kusmos.phsx.ku.edu/~melott/Astrobiology.htm