The asteroid is thought to have hit Earth with a force a billion times more powerful than the atomic bomb at Hiroshima.

Morgan said the "final nail in the coffin for the dinosaurs" came when blasted material flew into the atmosphere, shrouding the planet in darkness, causing a global winter and "killing off many species that couldn't adapt to this hellish environment."

Scientists working on the study analyzed the work of paleontologists, geochemists, climate modelers, geophysicists and sedimentologists who have been collecting evidence about the KT extinction over the last 20 years.

Geological records show the event that triggered the dinosaurs' demise rapidly destroyed marine and land ecosystems, they said, and the asteroid hit "is the only plausible explanation for this."

Peter Schulte of the University of Erlangen in Germany, a lead author on the study, said fossil records clearly show a mass extinction about 65.5 million years ago -- a time now known as the K-Pg boundary.

Despite evidence of active volcanism in India, marine and land ecosystems only showed minor changes in the 500,000 years before the K-Pg boundary, suggesting the extinction did not come earlier and was not prompted by eruptions.

The Deccan volcano theory is also thrown into doubt by models of atmospheric chemistry, the team said, which show the asteroid impact would have released much larger amounts of sulphur, dust and soot in a much shorter time than the volcanic eruptions could have, causing extreme darkening and cooling.

Gareth Collins, another co-author from Imperial College, said the asteroid impact created a "hellish day" that signaled the end of the 160-million-year reign of the dinosaurs, but also turned out to be a great day for mammals.

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

(Collins has created a website at http://impact.ese.ic.ac.uk/ImpactEffects/Chicxulub.html which allows readers to see the effects of the asteroid impact.)

(Editing by Myra MacDonald)