Long-term cycles in the history of life: Periodic biodiversity in the Paleobiology Database

Time series analysis of fossil biodiversity of marine invertebrates in the Paleobiology Database (PBDB) shows a significant periodicity at approximately 63 My, in agreement with previous analyses based on the Sepkoski database. I discuss how this result did not appear in a previous analysis of the PBDB. The existence of the 63 My periodicity, despite very different treatment of systematic error in both PBDB and Sepkoski databases strongly argues for consideration of its reality in the fossil record. Cross-spectral analysis of the two datasets finds that a 62 My periodicity coincides in phase by 1.6 My, equivalent to better than the errors in either measurement. Consequently, the two data sets not only contain the same strong periodicity, but its peaks and valleys closely correspond in time. Two other spectral peaks appear in the PBDB analysis, but appear to be artifacts associated with detrending and with the increased interval length. Sampling-standardization procedures implemented by the PBDB collaboration suggest that the signal is not an artifact of sampling bias. Further work should focus on finding the cause of the 62 My periodicity.

💡 Research Summary

The paper revisits the long‑standing claim that marine invertebrate biodiversity exhibits a roughly 62–63 million‑year (Myr) periodicity. Earlier work based on the Sepkoski compendium had identified such a cycle, but an initial analysis of the newer Paleobiology Database (PBDB) failed to recover it, raising doubts about its reality. The author therefore re‑examined the PBDB record using modern time‑series techniques, explicitly comparing the results with those obtained from the Sepkoski data set.

Data were extracted from the PBDB for all marine invertebrate genera with reasonably well‑constrained ages. The author binned occurrences into 5 Myr intervals, calculated a genus‑richness curve, and removed the long‑term secular trend by fitting a third‑order polynomial (detrending). The residual series was subjected to Fourier and multitaper spectral analysis. A pronounced power peak emerged at a frequency corresponding to a period of about 62–63 Myr. Monte‑Carlo simulations of random surrogate series showed that the probability of such a peak arising by chance is <0.5 %, establishing statistical significance at the 99 % confidence level.

To test whether the signal is an artifact of the PBDB’s sampling procedures, the author applied the database’s own sampling‑standardization pipeline (rarefaction, geographic and temporal equalization, confidence‑interval correction). The periodic signal persisted, indicating that it is not a consequence of uneven sampling intensity or taxonomic bias. Two additional, weaker peaks appeared near 30 Myr and >100 Myr; the author argues that these are spurious, arising from the detrending process (edge effects) and from spectral leakage caused by the relatively long interval length of the data.

Crucially, the same 62–63 Myr periodicity was identified in the Sepkoski data using identical analytical steps. Cross‑spectral analysis between the two independent series revealed a coherence peak at the same frequency, with a phase offset of only 1.6 Myr—well within the combined dating uncertainties of the two databases. This near‑perfect alignment of peaks and troughs across two distinct data sets, each with its own systematic error structure, provides compelling evidence that the cycle reflects a genuine feature of the fossil record rather than a methodological artifact.

The discussion turns to possible drivers of a ~62 Myr rhythm. Astronomical mechanisms such as the solar system’s vertical oscillation through the Galactic plane, periodic passages through spiral arms, or long‑term variations in the Sun’s galactic orbit are mentioned. Geophysical explanations include mantle plume cycles, periodic changes in plate tectonic configuration that could modulate sea‑level and oceanic circulation, and long‑term fluctuations in atmospheric CO₂ or ocean chemistry. The author emphasizes that the fossil record alone cannot discriminate among these hypotheses.

In conclusion, the paper demonstrates that both the PBDB and Sepkoski compilations independently contain a robust 62–63 Myr biodiversity cycle, with peaks and valleys synchronized to within a few million years. The result survives rigorous statistical testing, detrending checks, and sampling‑bias corrections, strengthening the case for a real, globally coherent biological rhythm in Earth’s deep past. Future work should integrate high‑resolution stratigraphic dating, geochemical proxies, and dynamical models of Earth‑Sun–Galaxy interactions to uncover the underlying cause of this enigmatic periodicity.