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West Coal and Pollen Shed Light on Global Catastrophe
West Coal and Pollen Shed Light on Global Catastrophe
23 Nov 2001
(Source: Institute of Geological & Nuclear Sciences)

Institute of Geological & Nuclear Sciences
Lower Hutt, New Zealand

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A New Zealand-led group of scientists has found the first evidence for global destruction of forests when a large asteroid hit the Earth 65 million years ago, killing off the dinosaurs.

Until now scientists believed that 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 a 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 worldwide.

The study by paleontologists Chris Hollis and Ian Raine of the Institute of Geological and Nuclear Sciences Limited, and Swedish researcher Vivi Vadja, is 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.

GNS scientists have a good knowledge of the Greymouth coalfield having mapped it in detail over many years.

Working on a hunch that the coal might contain the evidence they were looking for, Dr Raine chipped off pieces of the coal seam and brought them to Wellington where the microscopic pollen grains 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. The iridium concentration of 71 parts per billion is the highest known from non-marine rocks anywhere in the world.

These 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 sedimentary rocks in eastern Marlborough.

"Whether the forest destruction was caused by prolonged darkness and freezing conditions associated with the impact winter, or by global outbreaks of wildfires, is a matter for further study by the research team," Dr 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."

The research was supported by the New Zealand Marsden Fund, and the Swedish Wenner-Gren Foundation and Royal Physiographic Society.

Note: Sixty-five million years ago there were at least four types of dinosaur living in New Zealand. They included a sauropod, theropod, hypsilophodont, and ankylosaurid. There were also numerous marine reptiles. Bones of these creatures have been found in a stream north of Napier. Sixty-five million years ago New Zealand was about 1000km closer to the South Pole than it is today, and several degrees warmer than today. The Hawke's Bay stream where the remains of New Zealand's dinosaurs have been found is one of four sites in the southern hemisphere where the so-called "polar dinosaurs" have been found. The other locations are in Australia, the Beardmore Glacier Antarctica, and the Antarctic Peninsula.

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Last Updated: 26 Nov 2001