2010/05/20 by Vincent Courtillot, Frédéric Fluteau · 3 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Paleontology and Stratigraphy of Fossils #Geology and Paleoclimatology Research
paper · doi:10.1126/science.328.5981.973-b
openalex publication_date 2010/05/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/23
In their Review "The Chicxulub Asteroid impact and mass extinction at the Cretaceous-Paleogene boundary" (5 March, p. 1214), P. Schulte et al. conclude that "the Chicxulub impact triggered the mass extinction." However, the Review does not give sufficient and accurate consideration to the volcanic hypothesis. The authors claim that for Chicxulub, "the extremely rapid injection rate of dust and climate-forcing gases would have magnified the environmental consequences compared with more-prolonged volcanic eruptions." As evidence, they cite our paper (1), saying, "the injection of ∼100 to 500 Gt of sulfur into the atmosphere within minutes after the Chicxulub impact contrasts with volcanic injection rates of 0.05 to 0.5 Gt of sulfur per year during the ∼1-million-year-long main phase of Deccan flood basalt volcanism." This contains a substantial error and a fundamental misrepresentation of our paper. Half a Gt per year of sulfur for 1 million years amounts to 500,000 Gt of sulfur, which in any climate model would lead to a "snowball" Earth! In (1), we estimate the total amount of SO2 released by the traps at about 10,000 Gt, less by a factor of 50 than that in Schulte et al.'s Review. The Deccan erupted in a small number of short, huge pulses, reducing actual injection duration to far less than 1 million years. We and others (2, 3) have argued that two main phases likely lasted a few thousand to tens of thousands of years, during which individual flows would have reached volumes of 10,000 km3 and released up to 100 Gt of sulfur in one or a few decades (based on analysis of paleomagnetic secular variation). Schulte et al. use our study to show that volcanism did not lead to the extinction, yet we showed that injection of SO2 by a single volcanic pulse could have had a climatic impact similar to Chicxulub. We estimated (1) that the largest Deccan pulses emitted up to 100 Gt of sulfur at 0.5 Gt per year for a few decades to tens of decades, implying a radiative effect slightly lower but lasting substantially longer than in the impact case. Whereas impact was a single event, some 30 volcanic pulses emitted total amounts of SO2 not very different from Chicxulub. Their sequence would have generated a runaway effect not allowed by a single impact or volcanic pulse. Evidence of an association between extinctions and continental flood basalts (CFBs) arising from eruption has been proposed since at least 1986 (4–7). Subsequent work has shown that all extinction or oceanic anoxia events in the past 300 million years are associated with a large accumulation of igneous material of the same age within uncertainties (8). No conclusive impact has been demonstrated at any mass extinction boundary other than the Cretaceous-Paleogene. The case of the largest CFB (Siberian traps) and mass extinction (Permo-Triassic ∼250 million years ago) is now generally accepted. Without challenging the existence or age of the Chicxulub impact, we believe that it is increasingly arguable that it could not by itself have caused a mass extinction, but that because it took place demonstrably during Deccan eruptions (9, 10), it contributed significantly to the mass extinction, as yet another giant lava flow could have, in an already very weakened environment.