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Scientists seek to explain mass extinctions

It may be because 2012 is fast approaching – the year the Aztecs predicted life as we know it would end. But scientific journals are filling up with studies seeking to explain the planet’s past mass extinctions.

And they run hot and cold.

One team, out of Caltech, proposes that the Earth’s second largest mass extinction, 450 million years ago, was caused by a cooling climate.

While another team out of Canada suggests the largest mass extinction, called the “Great Dying,” which occurred 250 million years ago, was caused by volcanic and coal fire debris.

And finally, another team has evidence showing that at least some dinosaurs survived the mass extinction that was supposed to have wiped them all out 65 million years ago.

Whew. That’s a lot of extinction to be reported on in one week.

But here’s what they say.

The Caltech team was looking at what is known as the Late Ordovician mass extinction, 450 million years ago.

The extinction coincided with a glacial period. During this time temperatures cooled and glaciers grew. The continents were also in different places: North America was on the equator, while most every other continent was joined into one super continent called Gondwana.

Using a new tool that can tease out ancient global temperatures from sea ice – something that until now has been impossible – the researchers showed the Late Ordovician extinction events coincided with drops in global temperature and increases in glaciation.

“Our study strengthens the case for a direct link between climate change and extinction,” Seth Finnegan, a Caltech postdoctoral researcher and author on the paper, said in the news release.

The study appears in the journal Science.

Now fast forward 200 million years into the late Permian, or the Great Dying. In this case it was volcanoes that triggered the extinction of 96 percent of the planet’s marine species.

A team of researchers, led by Stephen Grasby of the Geological Society of Canada, shows that volcanoes triggered extensive coal fires that spewed toxic ash into the atmosphere, poisoning air and water.

Although this had long been a theory, Grasby’s team found some evidence.

In modern day coal-fired power plants, scrubbers are used to catch “fly ash” from the plant’s emissions. The fly ash is filled with toxic metals, such as chromium.

Looking at sediments collected from late Permian deposits, Grasby found high levels of chromium. This suggests that fly ash may have poisoned ancient lakes and oceans, contributing to the mass extinction.

"It's the first literal smoking gun to show that coal combustion was occurring," Grasby told New Scientist magazine.

Researchers will have to see if chromium is found in other Permian deposits to see how widespread the phenomena may have been.

The research was published in a letter to the journal Nature Geoscience.

And finally: Another Canadian research team has discovered that at least one dinosaur survived the mass extinction that killed those reptiles off between 65.5 and 66 million years ago. They reported their findings in the journal Geology.

A fossilized hadrosaur bone, found in New Mexico, has been dated at 64.8 million years old – a good 700,000 years after the late Cretaceous extinction event.

Maybe in 2013, a few of us will be so lucky?

 

Filed under: Environment, Daily Report

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