Asteroid wiped out dinosaurs
2001-11-22 14:08
Auckland - New Zealand scientists have discovered smoking gun evidence that dinosaurs were wiped out by an asteroid which hit the world 65 million years ago.
They found the evidence, tiny bits of pollen, in coal in the
remote West Coast of New Zealands South Island.
Government-run Institute of Geological and Nuclear Sciences
(GNS) palaeontologists Chris Hollis and Ian Raine, and Swedish
researcher Vivi Vadja, have had their study published in the latest issue of the international magazine Science.
The trio focused on pollen grains preserved in exposed coal
seams in a stream bank adjacent to the Moody Creek coal mine, north of Greymouth.
In a statement GNS said until now scientists believed
that the destruction of forests due to an "impact winter" or
impact-ignited wildfires was largely confined to the American
continent, within a radius of several thousand kilometres of the
inferred impact site on the Yucatan Peninsula, Mexico.
The New Zealand finding of the sudden death of a mixed forest
and rapid recolonisation by ferns on the opposite side of the Earth to the impact site is compelling evidence that the asteroid impact caused sudden destruction of terrestrial plants world-wide.
Working on a hunch that the coal might contain the evidence they
were looking for, Raine chipped off pieces of the coal seam and
brought them to Wellington where microscopic pollen grains within
the coal were studied.
The scientists found a mixed forest community had been abruptly
replaced by a few species of fern directly after the meteorite
impact.
The types of fern identified are known as early colonisers of
open ground.
Geochemical analysis of the coal showed extremely high
concentrations of the elements iridium, cobalt, and chromium, with the iridium concentration of 71 parts per billion the highest known for non-marine rocks anywhere in the world.
The three elements are known to be much more abundant in
meteorites than in the Earth's crust. They have been found at high concentrations before in New Zealand, but only where the impact layer is preserved in marine rocks in eastern Marlborough.
"Whether the forest destruction was caused by prolonged darkness
and freezing conditions associated with an impact winter, or by
global outbreaks of wildfires, is a matter for further study by the research team," Hollis said.
"Either way, however, it is no longer difficult to explain the
mass extinction of large herbivorous dinosaurs and their predatory cousins, especially in the southern hemisphere."
There were at least four types of dinosaur living in New
Zealand, including a sauropod, theropod, hypsilophodont, and
ankylosaurid.
Sixty-five million years ago New Zealand was about 1 100
kilometres (682 miles) closer to the South Pole than it is today,
but several degrees warmer than today. - AFP
- SAPA