Galactic forcing increases origination of marine microplankton (2509.04165v1)

Abstract: The continuous flux of Galactic cosmic rays that bombard Earth's atmosphere creates ionizing radiation that can damage the DNA of living organisms. While this radiation on Earth is relatively constant in the short term, large and long-scale fluctuations are expected with a period of $\sim 63.5$ million years. As the Solar System moves above or below the Galactic plane during its oscillatory motion about the Galactic center, the Galactic magnetic shielding weakens, allowing more cosmic rays to reach Earth and trigger mutations in organisms. We identify a significant correlation (weighted global p-value: $1.25\times 10^{-4}$, or $3.72\sigma$) between the Solar System's Galactic oscillations and the origination of marine zoo- and phyto-microplankton genera over the Phanerozoic. When we restrict the analysis to time intervals during which all four groups coexisted, a post-trial significance of $4.52\sigma$ emerges. Our findings suggest that changes in biodiversity have been significantly influenced by long-term Galactic forcing.

• The paper demonstrates that periodic increases in cosmic ray flux, due to Galactic forcing, significantly trigger the origination of marine microplankton genera over the Phanerozoic.
• The paper utilizes high-resolution fossil occurrence data and robust statistical methods, including Monte Carlo permutation tests, to establish the correlation.
• The paper suggests that cosmic ray-induced mutagenesis acts as an external evolutionary driver, with implications for understanding marine biodiversity patterns.

Galactic Forcing and the Origination of Marine Microplankton: Evidence from Phanerozoic Fossil Data

Introduction

This paper presents a comprehensive analysis of the correlation between the Solar System's oscillatory motion relative to the Galactic plane and the origination of marine microplankton genera throughout the Phanerozoic. The authors leverage high-resolution fossil occurrence datasets for four major microplankton groups—radiolaria, dinoflagellates, nannoplankton, and planktonic foraminifera—to test the hypothesis that periodic increases in cosmic ray flux, driven by Galactic dynamics, have significantly influenced evolutionary diversification in marine ecosystems. The paper employs rigorous statistical methods to quantify the association between cosmic ray exposure and origination events, providing strong evidence for a non-random, periodic driver of marine biodiversity.

Data Sources and Methodological Framework

The analysis utilizes curated, frequently updated databases for each microplankton group, ensuring taxonomic and stratigraphic accuracy. Origination curves are constructed from first appearance datums (FADs) at the finest available temporal resolution (stage/substage), calibrated to the Gradstein (2020) geologic timescale. The authors acknowledge and attempt to mitigate biases inherent in fossil preservation and stratigraphic assignment, though sampling standardization is limited by data availability.

To test the central hypothesis, a one-sided Monte Carlo permutation test is performed, evaluating whether new genus appearances are statistically associated with the Solar System's maximum excursions from the Galactic plane. The test statistic is the sum of new genera appearing during these intervals, with the null hypothesis positing no association. The Stouffer method is used to combine p-values across groups, accounting for correlated environmental effects.

Galactic Dynamics and Cosmic Ray Flux

The Solar System's orbit around the Galactic center is characterized by both radial and vertical oscillations, with a vertical period of approximately 63.5 Myr and amplitude of ~70 pc. When the Solar System is maximally displaced from the Galactic plane, Galactic magnetic shielding is reduced, resulting in increased cosmic ray flux reaching Earth. The attenuation of cosmic ray flux is modeled using established parameters for magnetic field strength and scale height, yielding a ~15% increase in 1 GeV cosmic ray flux during maximum excursions.

Cosmic rays initiate atmospheric air showers, producing secondary particles (muons, electrons, neutrinos, gamma rays) that penetrate the upper oceanic layers where microplankton reside. The muon component is particularly significant, contributing the majority of the radiation dose. Simulations indicate that high-energy proton showers deposit energy within the first ~10 meters of seawater, directly impacting planktonic organisms.

Statistical Results and Significance

The timing of new genus appearances in all four microplankton groups exhibits a strong correlation with the Solar System's vertical oscillation period. The global weighted p-value for the association is 1.25×10⁻⁴ when considering all genera data, and 3.76×10⁻⁶ for the interval of group coexistence (0–174 Ma). After Bonferroni correction for nested data samples, the post-trial significance reaches 4.52σ, exceeding the conventional 3σ threshold for discovery in astronomical contexts. Notably, the radiolarian record, which spans the entire Phanerozoic, is affected by pronounced blooming events (e.g., Middle Triassic), likely modulated by geomagnetic field minima in addition to Galactic effects.

Mechanistic Interpretation: Cosmic Ray-Induced Mutagenesis

The primary biological effect of increased cosmic ray flux is ionization, leading to the generation of solvated electrons in seawater. These electrons induce DNA double-strand breaks and other forms of genetic damage in microplankton, triggering error-prone repair mechanisms and increasing the rate of gene mutations. The resulting genomic instability can produce chromosomal rearrangements and large-scale phenotypic changes, facilitating the rapid origination of new genera. The actin-cytoskeleton system may play a regulatory role in DNA repair processes, further influencing evolutionary outcomes.

The paper posits that periods of enhanced cosmic ray exposure, driven by Galactic dynamics, act as external mutagenic forcing events, superimposed on background evolutionary processes and natural selection. This mechanism is supported by the observed periodicity and statistical significance of origination events in the fossil record.

Implications and Future Directions

The findings have substantial implications for understanding macroevolutionary patterns in marine ecosystems. The demonstrated link between Galactic forcing and microplankton origination suggests that long-term astronomical cycles are a significant, previously underappreciated driver of biodiversity. This challenges models that attribute diversification solely to terrestrial or localized abiotic events.

Practically, the results motivate further investigation into the interplay between geomagnetic field strength, Galactic magnetic shielding, and cosmic ray flux in modulating evolutionary rates. The approach can be extended to other fossil groups and simple life forms to assess the generality of the mechanism. Improved sampling standardization and integration of additional paleoclimatic and geochemical proxies will enhance causal inference.

Conclusion

The paper provides robust statistical evidence that periodic increases in cosmic ray flux, resulting from the Solar System's oscillatory motion relative to the Galactic plane, have significantly influenced the origination of marine microplankton genera throughout the Phanerozoic. The mechanism is plausibly mediated by cosmic ray-induced mutagenesis, with implications for the broader understanding of macroevolutionary dynamics. Future research should further elucidate the relative contributions of Galactic and terrestrial factors in shaping the evolutionary history of Earth's biosphere.