MAGNITUDE AND TIMING OF TERRESTRIAL BOLIDE IMPACTS: IMPLICATIONS FOR MASS EXTINCTION SEVERITY DURING THE MESOZOIC AND CENOZOIC

Thirty-one terrestrial impact structures suggest a possible correlation between the timing and magnitude of mass extinctions, and the occurrence and magnitude of large bolide impacts with the Earth. The severity of four mass extinctions during the Mesozoic and Cenozoic are suggested to be a function of the total kinetic energy received from extraterrestrial objects colliding with the Earth. Forty-one geologic ages (or epochs) spanning the Mesozoic and Cenozoic are analyzed using the terrestrial cratering record for kinetic energy (Mt TNT/age) from impacting extraterrestrial objects. Four of the identified Mesozoic and Cenozoic mass extinction events occur during geologic ages (or epochs) that exhibit a minimum impact energy of 1.0 x 10⁷ Mt TNT equivalent yield. Impact-induced mass extinctions are suggested for the Norian, Tithonian, and the Late Eocene, in addition to the well-documented Cretaceous-Tertiary event. These results also indicate that the occurrence of relatively synchronous multiple impact events are a possible cause of mass extinctions.

The forces of erosion and plate tectonics have served to remove and obscure the majority of the terrestrial cratering record, therefore it is impossible to prove the absence of an impact for a given geologic age. There are examples in the Mesozoic and Cenozoic where a mass extinction is indicated in the fossil record, but either minor or no impact structures are recorded within the corresponding geologic age. Therefore, other processes are responsible for causing these mass extinctions, or the impact structures that may correlate with these extinctions remain undiscovered. More research is required to corroborate or falsify correlations between large impact events and mass extinctions. As a result, further efforts should be made to improve our knowledge of the terrestrial impact record by identifying new structures, obtaining accurate ages for known structures, and by documenting the marine extinction record to the genus or species level.