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A new study by paleoecologist Margaret Fraiser at the University of Wisconsin, Milwaukee, offers an interesting new theory behind the cause of the Earth's largest extinction: copious carbon-dioxide

When most people hear the phrase "the earth's largest extinction", they think dinosaurs. 

Margaret Frasier knows better.  As a paleoecologist, she knows that the Earth's largest mass extinction of life occurred at the end of the Permian Period at the end of the Paleozoic Era; 252 million years before the first T-Rex ever walked the earth.  The extinction destroyed the large land amphibians' dominance of the land, and paved the way for dinosaurs to emerge as the dominant land species. 

University of Wisconsin-Milwaukee professor Margaret Frasier is studying this extinction avidly, looking for possible details to further our understandings of what might have caused this landmark event.

Her recent conclusions, published in an Elsevier journal [1] [2] (PDF) and detailed in a recent press release titled "When Bivalves Ruled the World," describe an Earth with run-away carbon dioxide levels.  She concludes that the Permian-Triassic mass-extinction was caused by toxic, oxygen-less oceans created by too much atmospheric carbon dioxide (CO2). 

The Permian-Triassic extinction event wiped out nearly 70 percent of species on land and 95 percent of sea species.

“Estimates of the CO2 in the atmosphere then were between six and 10 times greater than they are today,” Frasier states.  The largest continuous volcanic eruption on Earth – known as the “Siberian Traps” – had been pumping out CO2 for about a million years prior to the Permian-Triassic mass extinction.

Her hypothesis is that high CO2 levels at the close of the Permian Period caused global warming, greatly increasing global temperatures.  With no cold water at the poles, ocean circulation slowed, and the oceans were unable to mix with the little oxygen left in the air.

She cites a variety of evidence of high CO2 and low ocean oxygen levels in this fossil record.  One piece of evidence is darkened rock from underwater fossil strata of the time.  Darkening in ocean rock of this nature indicates a low amount of oxygen at the time of formation.

Frasier also collected evidence to support her theory in the form of bivalve fossils.  The only survivors of the extinction were bivalve mollusks and gastropods -- snails.  Only shallow water, tiny, small-shelled varieties with high metabolisms and a flat shape, which allowed them to spread out while feeding to extract more oxygen, survived.  Deeper water varieties, where there was less oxygen, and larger shelled varieties, which needed more oxygen, became extinct, disappearing from the fossil record.

A final piece of evidence cited is the disappearance of the coral reefs.  Coral reefs die if their environment lacks sufficient oxygen.


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RE: not just us...
By JasonMick (blog) on 9/1/2007 9:53:41 PM , Rating: 2
I said "large areas of the earth", not "the tropics".

I think you did not understand what I said, even though, oddly, you quoted me on it, which would seem to indicate that you did.

I agree with your statements on what the effect of modest warming would be. However, most people would not like to have to deal with tropical/near-tropical level heat. And more importantly if the water levels rise due to melting ice, large populations will be displaced. Also desertification would become an increasing problem. And then there are problems such as pest migration. Life would be less comfortable for large areas, I stand by my statement.

Anyways, I've had my say on this topic, so I am done for now. You will probably repost a disagreement to my comment, I suppose, sadly.


RE: not just us...
By masher2 (blog) on 9/1/2007 10:20:48 PM , Rating: 2
> "I said "large areas of the earth", not "the tropics"."

And I responded in kind. The upper latitudes would be affected positively. The tropics would be largely unaffected. That leaves only the temperate regions, which may be positively or negatively affected, but only to a small degree either way.

That's the whole world right there. There are no other "large areas" to be affected.

> "if the water levels rise due to melting ice, large populations will be displaced"

Sea levels are rising 2-3mm/year, same as they have been for the past 7,000 years. And if you assume that rate rises sharply-- so? Even then it means that, over the course of a couple centuries, a few million people will need to move. Want to guess how many millions of people have moved, of their own free will, to Florida just in the past 50 years?

When you're talking about such long time scales, a few million people moving isn't a problem. Its a far better (and cheaper) solution than radical proposals that drastically raise the cost of energy, thereby risking economic chaos and forcing third-world nations to remain undeveloped. Far better to let nations like Bangladesh develop a modern economy, so its people can easily afford whatever minor mitigation measures might be necesssary.


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