THE CONTRIBUTION OF INITIAL ENVIRONMENTAL CONDITIONS TO PHANEROZOIC BIOTIC EXTINCTION EVENTS

Periods of elevated extinction have occurred throughout Earth history, with extensive focus on the “Big 5” Phanerozoic mass extinctions, and the contribution of biotic and abiotic conditions occurring during these events. Notably, the influence of pre-extinction conditions on extinction magnitude has been virtually unaddressed, which is the purpose of this research. To test hypotheses of how specific “initial conditions” of abiotic environmental factors may have impacted extinction rates, we compiled a ~540 Myrs record of five environmental proxies and two published marine faunal extinction rate datasets (Bambach 2006 and Alroy 2014) from an extensive literature review. The environmental proxies tested include: δ¹⁸O and δ¹³C stable isotopic records (climate variability, including latitudinal gradients), ⁸⁷Sr/⁸⁶Sr record (continental weathering rates), eustatic sea level (variability in area of shallow shelf habitat), and continental shelf area (habitable area). All proxies were subset to 2, 5, and 10 Myrs-prior bins to test for time bin sensitivity. Multiple linear regression analysis was used to test for correlations between environmental factors (individually and in concert) and extinction rates during 18 and 14 key intervals of elevated extinction identified by Bambach (2006) and Alroy (2014), respectively. Preliminary results from the Alroy 5 Myrs-prior model found significant relationships between elevated extinction rates and initial environmental conditions. However, the early Dresbachian extinction was removed due to data gaps. Initial stable global temperatures, increasing carbon cycle instability, and increasing continental weathering rates work in concert to contribute to elevated extinction rates. Statistically significant relationships were not observed for the Alroy 10 Myrs-prior model. Reduced model observations via proxy data gaps made interpretations uninformative for all other models; current work is invested in improving sampling. Identifying the role that pre-existing conditions play in promoting or inhibiting periods of elevated extinction are important for improving our understanding of Phanerozoic macroevolution and may positively contribute to improving projections of the consequences of the current biodiversity crisis.