The Great Dying: Smoking Guns in Earth's Fossil Record

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By Lou Varricchio

MIDDLEBURY, Vt. USA — In the case of prehistory’s mass extinctions, astronomers and paleontologists have often been at odds. In 1980 Luis and Walter Alvarez, father and son scientists, found clues in the rocks that indicated an asteroid or comet impact at the end of the Cretaceous Period may have triggered the demise of the dinosaurs.

When the Alvarez team turned up evidence of a rare metallic element called iridium at the Cretaceous-Tertiary sedimentary boundary (iridium being found in meteorites far more than in the Earth’s crust) astronomers were quick to adopt the theory. However, paleontologists weren’t too sure.

Some geology experts were still able to demonstrate a slow decline in dinosaur species rather than a rapid die off as suggested by the Alvarezs. However, more than 30 years later, the Cretaceous impact theory is almost universally accepted by science. Yes, a few scientists still point to stubborn clues that suggest a long decline for the dinosaurs.

Now, a new debate over another mass extinction event is taking shape; some astronomers and paleontologists are again on opposite sides of the debate.

This time, the debate is focused on the greatest extinction in Earth’s fossil record—an event known as the Great Permian Extinction. At the end of the Permian 250 million years ago, nearly 95 per cent of life vanished in the oceans and 70 per cent on land.

A paleontologist has suggested that an extraterrestrial impact may be the cause of the Permian extinctions.
Dr. Peter Ward of the University of Washington outlined his impact ideas relating to the Great Permian Extinction in a popular 2004 science book, titled “Gorgon”.

Ward tells the story of uncovering the fossilized remains of giant mammal-like reptiles known as gorgons in Tertiary rocks of the Karoo Desert in South Africa. The  weird gorgons, and their kin, vanished at the end of the Tertiary leaving no evolutionary descendants. What caused their demise and the deaths of thousands of other species of animals and plants? The answer is slow to emerge.

Ward believes that a giant asteroid or comet impact triggered the extinctions. He points to circumstantial evidence (shocked quartz in some Permian-Triassic boundary rocks) that suggests this idea, yet other fossil experts strongly disagree with the data; they point to other clues that instead show a slow decline of species.

Recently, researchers at the University of Calgary announced that they had found the  smoking gun of the world’s biggest extinction. This time, it wasn’t an impact as Ward and others theorized. Instead, the Canadian scientists pointed to a series of massive volcanic eruptions, burning coal beds, and accelerated greenhouse gases as the reasons for the Permian deaths.

“We discovered layers of coal ash in rocks from the extinction boundary in Canada’s High Arctic that give the first direct proof to support this,” according to Dr. Steve Grasby, of the University of Calgary’s Department of Geoscience and a research scientist at Natural Resources Canada. “Unlike the end of dinosaurs, 65-million years ago, where widespread belief is that the impact of a meteorite was at least the partial cause, it is unclear what caused the late Permian extinction. Our research is the first to show direct evidence that massive volcanic eruptions—the largest the world has ever witnessed— caused massive coal combustion thus supporting models for significant generation of greenhouse gases at this time.”

Grasby says the culprit volcanoes were located in what is today northern Russia near the city of Tura. The volcanic fields covered an area 2-million-square kilometers in size—larger than all of Europe.

“The ash plumes from these volcanoes travelled to regions now in Canada’s arctic where coal-ash layers where found,” Grasby reports. “It was a really bad time on Earth. In addition to these volcanoes causing fires through coal layers, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in earth history.”

The jury is still out regarding the Great Permian Extinction. So, will it be the asteroid impact theory or the theories erupting volcanoes and burning coal seams? Stay tuned.

Louis Varricchio, M.Sc., was a science writer at the NASA Ames Research Center in California. He is currently a member of the NASA-JPL Solar System Ambassador Program.

CAPTION: A gorgon: Late Permian of South Africa. From Wikipedia.



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