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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: Hmm
By JasonMick (blog) on 9/1/2007 9:16:42 PM , Rating: 2
Well, I was just using your own unqualified statement, if we are nitpicking. I appreciate that you find me intelligent, and I have remind you that I have said many times that exponential growth is unpredictable.

The key thing that would cause the current trends to increase/decrease is massive deforestation, combined with the collapse of the plankton ecosystem. The former is undeniably in progress, while the latter is likely to occur as the oceans become increasingly polluted with highly concentrated chemicals that were formerly in land based rock deposits.

I expect the levels of CO2 to level off in growth slightly with the decrease of emissions, then increase exponentially, as deforestation cripples the CO2 fixation system of the earth's biosphere.

Deforestation is the chief threat to global warming. Also overpopulation/livestock are a big threat, as well. Cows produce more CO2 than cars. The combination of more CO2 produced, less fixed, growing on both ends, is an exponential situation, which will continue to happen until we stop cutting down the forests AND the population stops growing. That is unlikely to happen for some time, I think you would agree. Its good that emissions are declining, but we have to still find solutions to these two major problems, I think you would agree.

Ah, but the Devonian event wasn't due to species extinction, but rather a simple decrease in the rate of speciation, stretching over several million years.

Did you read the linked article Michael? It states:

"A major extinction occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, (the Frasnian-Famennian boundary), about 364 million years ago, when nearly all of the fossil agnathan fishes suddenly disappeared...The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef-systems, including the stromatoporoids, and the rugose and tabulate corals. The reef system collapse was so severe that major reef-building (effected by new families of carbonate-excreting organisms, the modern scleractinian corals) did not recover until the Mesozoic era."

Sounds like more than "decrease in the rate of speciation to me". In fact, this extinction, was among the five largest in history.

though this is not true for the Permian event, in which both species count and biomass decreased

So you are agreeing that the biomass decreased and my hypothesis could be possible??

Why put out an argument against my hypothesis based on facts you subsequently say were not true for the situation I am making the hypothesis for? That makes no sense. I was talking about the Permian, so my hypothesis, by your own admission remains a possibility.

RE: Hmm
By masher2 (blog) on 9/1/2007 10:04:10 PM , Rating: 3
> "Sounds like more than "decrease in the rate of speciation to me".

Paleobiologists disagree with you then. Let me quote:
Low origination contributed more than high extinction to the marked loss of diversity in the late Frasnian

In other words, the "extinction event" of the Late Devonian was driven primarily by new species failing to appear, rather than existing species disapearing. It was an event that took millions of years obviously.

And in any case, the CO2 levels during the late Devonian were falling rapidly, which makes your point doubly moot.

> " deforestation cripples the CO2 fixation system of the earth's biosphere."

Believe it or not, forests are a relatively minor portion of overall carbon fixation. A young, actively growing forest contributes a great deal...but old-growth forest (including rainforest) is a relatively static quantity, neither fixing nor releasing carbon in significant amounts.

In fact, recent research suggests that forests in the temperate zones may actually increase global warming. Their relatively minor contribution to carbon fixation being more than outweighed by the increased albedo they bring to the surface.

> "Why put out an argument against my hypothesis based on facts "

Because I'm not sure what your hypothesis is. I originally thought you were trying to link the Permian event to modern-day global warming, but you insist otherwise. So what exactly are you trying to suggest with all this?

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