November 14, 2002. Copyright 2002. Graphic News. All rights reserved.

Traces of Triassic impact found in England

LONDON, November 14, Graphic News: Debris from an ancient, extraterrestrial impact crater has been found in Britain, says a team of UK scientists. If further work confirms the age of this unusual find, the debris trail could shed more light on the sudden rise of the late Triassic dinosaurs about 227 to 202 million years ago.

Geologists have identified 160 or so known extraterrestrial impact craters during the so-called Phanerozoic age -- the half-billion years since life appeared on Earth. While impact craters are common, deposits of ejected material are much more rare say the researchers, writing in the latest issue of the journal Science.

Dr. Gordon Walkden and Dr. Julian Parker at the University of Aberdeen, and Dr. Simon Kelley at the Open University discovered characteristic impact ejecta -- consisting of small spheres of emerald green clay known as spherules, and shocked quartz -- in a Triassic-age deposit near Bristol in southwestern England.

Shocked quartz is a structurally-altered form of quartz that is created only by a sudden application of extremely high pressure to sand. Scientists have discovered that shocked quartz occurs only in two environments on Earth: in craters made either by an atomic bomb or a meteor impact.

Using X-ray diffraction analysis the researchers were able to detect tell-tale microscopic lines known as Òshock lamellaeÓ which indicated that atoms in the crystal lattice structure of the quartz had ÒshiftedÓ slightly to the side relative to adjacent planes of atoms.

Isotopic dating of other silicate minerals in the deposit suggests a tentative age of 214 million years for the debris. This is in the age range for several known Triassic craters, but the age and the thickness of the deposit match most closely with data from the 100-km (62-mile) diameter Manicouagan crater in northeastern Canada.

Before the days of the dinosaurs the EarthÕs continents were all connected in one huge landmass called Pangea. In this supercontinent the tectonic plates that were later to become North America and Europe were squeezed together and located much further south, roughly where the Caribbean is today.

Based on a late Triassic plate reconstruction, the thickness of the ejected material, impact angles and velocity as well as the EarthÕs rotation, Walkden and his co-authors estimate the material came from the 213-215 million-year-old Manicouagan, about 2,000 km (1,240 miles) away, rather than a much smaller impact crater about 650 km (400 miles) away at Rochechouart, France.

ÒFrom first approximation thickness modelling, Manicouagan may be a source for the layer, but we cannot rule out the possibility that the ejecta may be from the Rochechouart crater or from both craters as part of a multiple impact event,Ó say the researchers.

The discovery adds to the evidence that an asteroid or comet impact on Earth may have paved the way for the sudden rise of the great Jurassic dinosaurs.

Around 225 million years ago, large plant-eating dinosaurs grazed the Earth alongside primitive meat-eaters about the same size as a modern-day ostrich. After a mysterious event at about the time of the Triassic impacts the herbivores dwindled and large carnivores flourished. The precursors to Tyrannosaurus Rex were born.

Evolutionists believe that only the hardiest creatures would have survived the extreme conditions following an asteroid impact. Dust clouds masking the Sun would have plunged the Earth into dark cold, followed by intense warming as clouds of greenhouse gases accumulated.

Only warm-blooded animals that could withstand the cold or those that scavenged varying types of food would have had a survival advantage -- and these were the Jurassic dinosaurs.

These large dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic species. Dinosaur diversity reached a stable peak within 100,000 years of the end of the Triassic period.

These fierce creatures continued to rule the world for the subsequent 135 million years until a catastrophe -- believed ironically to be another meteorite impact -- led to their extinction 65 million years ago.
/ENDS

Sources: Science; Nature; Meteorite craters and impact structures of the Earth, Cambridge University Press