Links between asteroid impacts and mass extinctions in the Phanerozoic are the subject of a comprehensive review article by Grzegorz Racki and Christian Koeberl (University of Vienna) that has just been published in the prestigious Elsevier journal “Earth-Science Reviews”. There has been no confirmation of impact as the cause of the Big Five mass extinctions, except of course for the one at the Mesozoic-Cenozoic transition that wiped out the dinosaurs. Many of the hypotheses that are still being repeated are clearly wrong, e.g. concepts based on supposed giant end-Permian impact craters, interpreted solely on the basis of geophysical research. The evidence suggests that this and many other extinctions in the Phanerozoic were caused by an imaginable volcanic cataclysm.
However, the authors show that there is a continuum in the response of the Earth’s biosphere to asteroid impacts. By analysing the biotic changes associated with other large impact craters of about 100 km in diameter, it becomes likely that such collisions were one of the causes – in addition to the volcanic factor – of some secondary stepwise ecological crises. The main candidate is the Late Triassic (Norian) crisis, which could have led to the extinction of the so-called mammal-like reptiles (synapsids) known from Silesia – the large dicynodonts.
On the other hand, it is well known that such deadly impacts from space, such as the one at the end of the Cretaceous period, occur on average every 100 million years. The article examines the likelihood of giant asteroids falling into the oceans in the context of the sedimentary record of megatsunami and seismicity suggested by some researchers. The major Kellwasser Crisis in the Late Devonian seems to be a possible case of such a mysterious cataclysm. In summary, the authors claim that of the 18 known extinction events, there is one confirmed mass extinction (caused by a giant asteroid impact) and possibly 3-4 (“impact-enhanced”) biotic crises.
Source: Racki G., Koeberl C., 2024. Impact catastrophism versus mass extinctions in retrospective, perspective and prospective: Toward a Phanerozoic impact event stratigraphy. Earth-Science Reviews 259, 104904, 1-60. https://doi.org/10.1016/j.earscirev.2024.104904.
