Revealed: The day the dinosaurs were wiped from the earth

Published on Thursday 4 March 2010 22:04

DINOSAURS were wiped out by an asteroid the size of the Isle of Wight that hit the Earth with the explosive power of a billion atom bombs, scientists have concluded.

• Tyrannosaurus rex died out after a giant meteorite hit Mexico. Picture: PA

A new report from 41 international experts discounts an alternative theory that volcanic eruptions ended the reptiles' 160 million-year reign.

The scientists reviewed 20 years' worth of evidence in search of a definitive answer to the mystery of what happened to life on Earth about 65 million years ago.

More than half of all species on the planet, including the dinosaurs, flying pterosaurs and large marine reptiles, vanished in the Cretaceous-Tertiary (KT) mass extinction.

The leading theory has been a large asteroid impact off the coast of Mexico.

However, some scientists have argued that a series of volcanic super-eruptions in India may have been to blame for the catastrophe.

The eruptions spewed 1,100,000 cubic kilometres of lava across the Deccan Traps – a large volcanic region of west-central India – over a period of 1.5 million years.

It has been claimed that volcanic gas and debris could have led to atmospheric cooling and acid rain on a global scale.

But the new review has come out strongly in favour of the extinction being caused by a massive asteroid impact.

The gigantic space rock, measuring about 15km across, slammed into the Earth at Chicxulub, off the Yucatan peninsular.

Dr Gareth Collins, one of the scientists from the Department of Earth Science and Engineering at Imperial College London, said: "The asteroid was about the size of the Isle of Wight and it hit the Earth 20 times faster than a speeding bullet.

"The explosion of hot rock and gas would have looked like a huge ball of fire on the horizon, grilling any living creature in the immediate vicinity that couldn't find shelter.

"Ironically, while this hellish day signalled the end of the 160 million-year reign of the dinosaurs, it turned out to be a great day for mammals, who had lived in the shadow of the dinosaurs prior to this event.

"The KT extinction was a pivotal moment in Earth's history, which ultimately paved the way for humans to become the dominant species."

The asteroid hit with a force one billion times greater than the power of the atom bomb dropped on Hiroshima at the end of the Second World War.

It would have caused fire storms and earthquakes, and blasted material high into the atmosphere, blocking out the sun to trigger a "nuclear winter" that would have killed off much of the planet's life in a matter of days.

One key piece of evidence was the abundance of iridium in geological samples around the world from the time of the extinction, said the researchers, writing in the journal Science.

Iridium is very rare in the Earth's crust but very common in asteroids.

Rock layers immediately above the one containing the iridium reveal a dramatic decline in fossil numbers and species, indicating a mass extinction very soon after the asteroid impact.

Another link with the asteroid is evidence of "shocked" quartz in geological records.

Quartz undergoes a change of structure when hit very quickly by a massive force, and "shocked" quartz is usually only found at nuclear explosion and meteorite impact sites.

An abundance of shocked quartz has been found in 65 million-year-old rock layers all around the world at the "KT boundary".

In contrast, evidence for the volcanic explanation for the extinction was weak, said the scientists.

Although the eruptions on the Deccan Traps lasted a significant length of time, marine and land ecosystems showed only minor changes within the 500,000 years before the time of the Cretaceous-Tertiary extinction.