(Reuters) - A giant asteroid smashing into Earth is the only
plausible explanation for the extinction of the dinosaurs, a global
scientific team said on Thursday, hoping to settle a row that has
divided experts for decades.
SCIENCE
A panel of 41 scientists from across the world reviewed 20 years'
worth of research to try to confirm the cause of the so-called
Cretaceous-Tertiary (KT) extinction, which created a "hellish
environment" around 65 million years ago and wiped out more than
half of all species on the planet.
Scientific opinion was split over whether the extinction was caused
by an asteroid or by volcanic activity in the Deccan Traps in what
is now India, where there were a series of super volcanic eruptions
that lasted around 1.5 million years.
The new study, conducted by scientists from Europe, the United
States, Mexico, Canada and Japan and published in the journal
Science, found that a 15-kilometre (9 miles) wide asteroid slamming
into Earth at Chicxulub in what is now Mexico was the culprit.
"We now have great confidence that an asteroid was the cause of the
KT extinction. This triggered large-scale fires, earthquakes
measuring more than 10 on the Richter scale, and continental
landslides, which created tsunamis," said Joanna Morgan of Imperial
College London, a co-author of the review.
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.