Published on June 29th, 2020 | by Liz Martin-Silverstone

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Episode 112: Extinction of the dinosaurs

The end-Cretaceous (or K-Pg) extinction is one of the best known mass extinctions in Earth’s history, primarily because that is when non-avian dinosaurs disappeared. Although the popular idea is that an asteroid impact was what caused the extinction, the science hasn’t actually been that clear. More recently, a second hypothesis has challenged the idea asteroid as the main culprit, suggesting that huge volcanic eruptions in what is now India called the Deccan Traps was responsible. It has also been suggested that dinosaurs were already in decline when these things happened, speeding up the inevitable.

In this interview, we speak with Dr Alessandro Chiarenza, a research associate at University College London about his new paper published today in PNAS showing that it really was the asteroid impact that killed the dinosaurs. This new study, based on research he did during his PhD at Imperial College London, uses a large amount of data put into climatic models to analyse different scenarios caused by an asteroid impact, the Deccan Traps volcanism, and a combination of the two. This study showed that the asteroid caused a prolonged impact winter, causing the extinction of the dinosaurs.

Paper: Chiarenza, A. A., Farnsworth, A, et al. 2020. Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction. Proceedings of the National Academy of Sciences.

An asteroid 10 to 12 km wide hits central America 66 million years ago: this catastrophic event affected global climate causing a cascading effect on ecosystems worldwide, the so called End-Cretaceous mass extinction.

An individual of Ankylosaurus magniventris, a large armoured dinosaur species, witnesses the impact of an asteroid falling on the Yucatán peninsula 66 million years ago. Not even its large size and thick armour sheltered its kind from the violence of this cosmic disaster. The global consequences of this event on Earth and the whole biosphere caused the End-Cretaceous mass extinction. Image by Fabio Manucci.

Despite this obvious, ‘smoking gun’, cause of the K-Pg extinction, massive volcanic eruptions in India could also have been a contributing factor. The Deccan Traps (Figured, purple) are a large volcanic province characterised by expansive flood basalts, estimates suggesting that over 10 million km³ of magma was erupted. Due to the continued expulsion of gasses, these eruptions would have had a detrimental effect on the climate.

A: Temperature through the K-Pg mass extinction. The timing of prolonged volcanic activity is indicated by black arrows. Dinosaur fossil deposits are recovered up until the end of the Cretaceous and are still present during times of volcanic activity. The localities and times from which these dinosaur remains can be found are numbered and correspond to the map in B.
B: Locations of dinosaur-bearing fossil deposits in the Maastrichtian (Latest Cretaceous). 1. Hell Creek (USA); 2, Lamenta Formation (India); 3, Tremp Formation (Spain); 4, Phosphorite beds (Morocco); 5, Marilia Formation (Brazil); 6, Nemegt Formation (Mongolia).

To test whether the impact or the volcanism had a greater impact, Dr Chiarenza produced model simulations of the two competing hypotheses and their effect on dinosaur habitable areas (in red). Only the asteroid impact causes an abrupt eradication (blue) of the climatic niche for dinosaurs, generating a “blue screen of death” for non-avian dinosaurs.

Maps of habitat suitability of non-avian dinosaurs for different extinction scenarios. Red = high suitability; blue = low suitability.
F & G shows the suitable habitats at the time of impact (F) and subsequent recovery (G) with volcanism discounted. H & I show the impact (H) and recovery (I) with active volcanism.

Whether modelled with (Sc13) or without (Sc11) volcanism, the impact left no suitable area for the non-avian dinosaurs to survive. It was the impact that killed the dinosaurs.

Over longer time scales, the volcanism did increase the suitability of habitats. Following the impact (left), the temperature rapidly dropped, however the volcanism helped return higher temperatures (green band) than would have been possible otherwise (blue band).

Dr Alessandro Chiarenza

Top image: Davide Bonadonna