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The myth of the extinction of the dinosaurs

2 October 2010

The Chicxulub meteor impact

Boom!

Picture the scene: a herd of elephant-sized Iguanodon is grazing peacefully on some ferns and shrubs by the edge of a forest. A single Ancylosaurus walks slowly down towards the nearby river to drink, looking somewhat like a mix between a tortoise and a battle tank. In the late afternoon sky giant Pterodactyls circle on the hot thermals, high above the ground. Then suddenly, a flash in the corner of your eye, a streak of light across the sky. You look up and see a huge fire ball hurling towards the ground. Seconds later a silent blinding flash on the horizon, followed by a terrible thunderous shock wave that destroys everything in its path. It’s like the detonation of hundreds of atom bombs – it’s the end of the dinosaurs1.

We’ve seen it in films and in documentaries on television and it’s a dramatic image, a fitting end to such a collection of magnificent beasts. There’s only one problem – it probably never happened. It’s the myth of the extinction of the dinosaurs.

Ok, so the extinction itself is no myth: most of the dinosaurs did go extinct by the end of the Cretaceous, some 65 million years ago (known as the K-T extinction). Rather, it’s the notion that it was caused by a huge meteor strike that is a bit stupid and arrogant. But lets go through the facts one by one.

The Chicxulub meteor impact is supposed to have caused global wild fires that burned down most of the vegetation, leading to mass starvation for the herbivorous dinosaurs and ultimately (when the herbivores were all gone) for the carnivores as well. It’s a neat theory, and it’s partially supported by the fact that you can find sooth in many places from that period of time. But – sooth can be carried far by winds, even to the other side of the planet, so in itself it’s no proof of world wide fires. What we need is deposits of burned wood, ie charcoal, in sites all over the world. And we find none – not even in North America, which was just next to the impact site in the Gulf of Mexico. On the contrary, we find loads of non-burned plant material instead, something you wouldn’t expect to find after a raging global wild fire.

Red-eyed tree frog

“I might not look tough, but I survived the dinosaurs!”

The next event is supposed to be a wide spread acid rain, triggered by the dust from the impact. It is said to have been as strong as battery acid, destroying most of the vegetation and again causing mass starvation and extinction. The problem with this is that not all animals went extinct, and some of the ones that survived are not among the hardiest of creatures – the amphibians. Frogs and salamanders are very susceptible to acid, and don’t do very well at all in such environments: it interferes with their reproductive cycle, making it impossible for their eggs and larvae to develop. In spite of this, we see no mass extinction among amphibians during this period. In fact, they don’t seem to have been affected at all. This means that there could not have been global rain the strength of battery acid at the K-T extinction.

The final effect of the Chicxulub meteor impact is supposed to be that the sun was blocked out by a thick layer of dust in the atmosphere, causing a global winter for several months (if not years). Again, this doesn’t work because of the amphibians: just as they are sensitive to acid, they are also poor at withstanding sudden cold for extended periods of time – they would simply freeze to death. And since they didn’t, it couldn’t have happened.

But the real clincher in this whole story is the fact that the dinosaurs didn’t go extinct at the moment of the impact. In fact, they had started to disappear millions of years before Chicxulub, just like a whole range of other animals that didn’t survive the K-T extinction either. This gradual process was probably caused by climactic changes in the form of global cooling, due to the extremely high level of volcanic activity in the Deccan traps in India at the time. So the dinosaurs were already going extinct due to an ecological collapse when the Chicxulub meteor entered the scene – even without the impact they were doomed, and would have been gone within another million years our so.

The Chicxulub impact crater is real, and huge meteor did hit Earth some 65 million years ago. But it wasn’t the only or the biggest meteor impact in history. We’ve been hit many times, and rarely does these meteor impacts coincide with any mass extinction. It seems like a big hit from a space rock just isn’t enough to trigger a mass extinction event on its own. So the Chicxulub meteor did not cause the K-T extinction – it was just the final nail in the coffin for an amazing group of animals that happened to get extremely unlucky at the end of the Cretaceous.

1) The term “dinosaurs” in this post refers to non-avian dinosaurs, ie all dinosaurs except birds.

Written on my Android phone using the WordPress application.

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