How dinosaurs failed to rule the earth

DR PAUL ELLIOT, a lecturer in chemistry at the University of Huddersfield, looks at the latest theories for the extinction of the dinosaurs

Asteroid collision had force of billion bombs

SIXTY-SIX million years ago in the Cretaceous period, the planet was ruled by dinosaurs. Some 500,000 years later, a mere tick of the planetary clock, the majority of them were extinct.

The end of the Cretaceous and the beginning of the Paleogene period 65.5 million years (the so-called K-Pg event) marks one of the most cataclysmic events in the history of the Earth.

Last week in the journal “Science”, 41 researchers from around the globe published a review of all the evidence relating to the extinction of the dinosaurs and the K-Pg event and confirmed the hypothesis that the impact of a large asteroid from space was to blame.
The site of the impact lies at the end of the Yucatan peninsula in the Gulf of Mexico. The rock that made this crater is estimated to have been 10-15 km wide, roughly the size of Leeds, and hit the Earth at an astonishing 20km per second. The impact would have released the energy equivalent to one billion Hiroshima atomic bombs exploding at once.

While a tiny rock compared to the size of the Earth, the collision had globally devastating consequences.

Immediately on collision, anything within a few hundred miles would have been incinerated. The impact, almost punching straight through the Earth’s crust, would have triggered massive earthquakes. Huge tsunami waves would have been triggered, sweeping across the surrounding oceans, devastating the shorelines on the other sides. But these were just the immediate effects.

The impact threw up billions of tonnes of rock and dust which then rained down over the entire surface of the planet, covering vegetation.

This layer in the rock strata can be found around the world and, formed from the fall out from the impact, is one of the most important pieces of evidence for the collision.

This layer of rock is unusually rich in the element iridium, an element far more common in meteorites and asteroids and so indicates that it was formed from the debris. This layer also contains minerals such as shocked quartz that are only formed in such violent events which rained down in the debris.

But it was the thick dust high in the atmosphere that was the ultimate killer. Blocking out sunlight, the global temperature plummeted and, unable to photosynthesise, plants withered and died. As a result, whole ecosystems collapsed, taking with them many of the dinosaur species.

Many did survive however, including those that evolved into modern birds. The devastation also provided new opportunities to be exploited that led to the evolution of higher mammals, and ultimately, humans. This wouldn’t have happened if not for the asteroid impact 65 million years ago.

But could it happen again? There are still thousands, if not millions, of large rocks out there with the potential to hit Earth at some time in the future. Impacts of this magnitude are calculated to happen on average every 100 million years but smaller, but still heavily damaging, events can occur a lot more often.