so, what really killed the dinosaurs?

A group of scientists has been arguing that the dinosaurs' fate was sealed long before the asteroid hit. Now, supercomputers are putting this idea to the test.

Dinosaurs are just about every kid’s, and not-dead-inside-yet adult’s favorite group of animals regardless of their extinct status. It makes perfect sense. They were massive, loud beasts with huge claws, enormous fangs, and necks as long as a bus. Many even flew, or evolved to fly after the cataclysm which ended their 165 million year reign of Earth. Hell, what’s not to love? Except, we’ve been picturing them, and how they lived wrong for well over a century now, their images and our ideas of how they behaved in primeval forests and plains constantly adjusting to new discoveries. Even their deaths are still potentially up for debate.

Now, now, it’s very important to note that no one is disputing that an asteroid roughly the size of a Himalayan mountain slammed into our world 65 million years ago and, to use very technical and nuanced terminology, wrecked the entire planet’s biosphere’s shit pretty badly. We’re talking about tsunamis the size of skyscrapers and the Earth being pelted with a cloud of debris the size of New Zealand, the friction of thousands of impacts per hour heating up the atmosphere until it was as hot as an oven. Pretty much anything on the surface literally broiled, most likely creating the very first dino nuggets for the cold, dark, sulfuric aftermath.

Yet, say some scientists, despite the fact that the asteroid did slam into the Earth and was utterly devastating, maybe the dinosaurs managed to survive. After all, it was one event, and while food would be scarce since the food chain would have collapsed with the air choked in post-impact dust, these creatures were resilient. They were, after all, products of the worst mass extinction on record, so far, and found a way to dominate every ecological niche on the planet. Why couldn’t they do it again? Sure, all the giant beasts would be doomed, but things like raptors the size of a turkey and with limbs to burrow could’ve made it through. In fact, we know some did and became birds.

why is it always the volcanoes?

If we were to accept this premise, however, what did kill the dinosaurs? The critics of the asteroid theory point to the Deccan Traps, a massive basalt flow in India, which by the time of the Chicxulub impact was erupting non-stop for thousands of years. Their idea is that either the Traps had dwindled dinosaur populations to the point where the asteroid simply put them out of their misery, or the asteroid delivered the first mighty blow and the basalt flows finished the job. They can get quite heated about this if you ask them, with one of the leading proponents of the Deccan Trap theory going as far as to call the asteroid impact a “just right fairy tale.”

Before you dismiss her and other volcanic enthusiasts, you should know that there’s some interesting evidence on their side, with dinosaur fossils in Mexico seemingly thinning out over 300,000 years rather than immediately. That’s awfully close to the impact site and raises some interesting questions. Sure, some dinosaurs may have gotten flash-fossilized during the cataclysm and are well represented in the record, but then the number of species should have plummeted almost overnight, not after hundreds of thousands of years. Armed with these discoveries, scientists are more and more open to consider this so called two punch theory.

There’s even a hybrid version which says that the Chicxulub impact rattled the Earth so hard that it triggered another eruption of the Deccan Traps, which were already flowing in 30,000 year bursts over nearly half a million years. It’s that next half million year cycle of eruptions that would have doomed the dinosaurs. It sounds like a great merger of the competing ideas, but not so fast. It turns out that dating the decay of radioactive isotopes in zircon crystals yields an eruption date prior to impact, which suggests that the asteroid may not have caused the final volcanic tantrum ensuring that dinosaurs and nearly two thirds of all life would be snuffed out.

the wild, wild end of the cretaceous

But how would any two punch scenario actually play out? The asteroid theory is very straightforward. The physical impact, the fallout, and the shroud of dust and a cloud of sulfur dioxide that would’ve cooled the planet for several decades did virtually all the damage. By contrast, the Deccan Traps would have emitted carbon dioxide, 10.4 trillion tons of it to be exact, over the course of a million years. It also emitted a whole lot of sulfur dioxide, which cools the planet by reflecting sunlight. However, it sent a trillion fewer tons less of the latter, resulting in a steadily warming Earth with acid rains and more hostile oceans, sabotaging food chains.

According to 300,000 converging climate simulations to understand the exact mix of atmospheric gasses across the fossil records, the Deccan Traps would’ve made the end of the Cretaceous much hotter, drier, and more acidic. Then, just as life began to adapt to this new environment, the Chicxulub asteroid chilled the planet as the Traps just kept on erupting. When the dust from the impact settled, we’re right back to the previous hothouse that’s once again purging the biosphere of species that no longer had a chance to adapt before the next wild swing of the climate. Finally, the Deccan Traps stopped erupting, the climate settled, and selective pressures stabilized.

All of this isn’t just a passing curiosity, a way to settle a technical debate. Right now, we’re emitting carbon dioxide a hundred times faster than the Deccan Traps during the Cretaceous-Tertiary extinction or the Siberian Traps of the Permian extinction, an inauspicious sign. We could be creating our own mass extinction right now, so if we know what massive natural emissions can do when left unchecked, we can figure out the worst case scenarios for our own climactic misdeeds, how they’ll play out, and at what point we’ll know that we’re doing long term damage. If we can now dodge blows from asteroids, unlike the dinosaurs, why shouldn’t we avoid climate change too?

See: Renne et al. (2015) State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact. Science, DOI: 10.1126/science.aac7549

Schoene, B. et al. (2019) U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction. Science, DOI:10.1126/science.aau2422

Cox, A., Keller, C., (2023) A Bayesian inversion for emissions and export productivity across the end-Cretaceous boundary. Science, DOI:10.1126/science.adh3875