View Full Version : Low Oxygen Accelerated the Great Dying

2005-Sep-10, 01:16 PM
SUMMARY: The biggest mass extinction in the Earth's history happened approximately 250 million years ago. During the "Great Dying", more than 90% of creatures in the ocean, and 75% of life on land went extinct. What caused the extinction is still up for debate, but a researcher from the University of Washington thinks that low levels of oxygen in the atmosphere sure didn't help. Oxygen went down to 12% (currently it's 21%), and this made standing at sea level the same as being atop a 5,300 metre mountain (17,000 feet).

View full article (http://www.universetoday.com/am/publish/low_oxygen_great_dying.html)
What do you think about this story? post your comments below.

2006-Oct-22, 08:07 AM
A major catastrophe 251 million years ago left life teetering on the brink of oblivion. Now for the first time we have a clear picture of what caused it, says leading palaeontologist Michael Benton
251 million years ago, at the end of the Permian period, life on Earth was almost completely wiped out by an environmental catastrophe of a magnitude never seen before or since. All over the world complex ecosystems were destroyed. In the sea, coral reefs, fishes, shellfish, trilobites, plankton, and many other groups disappeared. On land, the sabre-toothed gorgonopsian reptiles and their rhinoceros-sized prey, the dinocephalians and pareiasaurs, were wiped out forever. Only 5 per cent of species survived the catastrophe, and for the next 500,000 years life itself teetered on the brink of oblivion. What terrible event could have wrought such havoc?
Two theories have been proposed - the impact of a huge meteorite or comet over 10 kilometres in diameter, or a massive and prolonged volcanic eruption. Up to now the evidence has been equivocal. But the data has been accumulating over the past 10 years, and the picture is now clear enough to say with some certainty what happened.

Read more (http://palaeo.gly.bris.ac.uk/Essays/wipeout/default.html)

2006-Oct-22, 05:43 PM
Interesting read. It seems that a 6 degree rise in temperature was enough to cause the methane trapped in the oceans to be suddenly released. Some estimates of current temperature rise suggest that much or more rise over the next 100 or so years. Makes one wonder.

2006-Oct-23, 12:44 AM
Read more (http://palaeo.gly.bris.ac.uk/Essays/wipeout/default.html)

Thanks for posting this. I've been reading about the Permian Extinction for quite awhile. I'm fascinated with the topic. Read Benton's book, Ward's, etc.

Yes, certainly the Siberian Traps messed up the planet pretty well. But what I wanted to know was what caused the Siberian Traps. What caused the planet's tectonics to go haywire like that, after millions of years where everything was going nicely? Does Earth "just happen" to go nuts every now & then and belch out huge amounts of gases??

I don't think so. Personally I think there had to be an impact, something huge enough to fracture the Earth's crust and send shockwaves thru the planet and cause great big fractures somewhere opposite the impact. (Antarctica is pretty much opposite of Siberia.) It is a pretty compelling coincidence that there was also a volcanic event (the Deccan Traps) at the same time as the other big impact at the Cretaceous.

I have read all the articles where they say "there's no evidence
of an impact at the P-T boundary". Well, no, because 250 million years is a long time and rocks are buried, eroded, folded under, etc. For some reason, a lot of these guys seemed reluctant to say there could have been an impact. I can't figure out why.

This is just an emotional bias, but I'd much rather believe that something nasty from space was responsible (we already know how comets & asteroids have affected other planets in our solar system) than to believe that Earth just happened to start malfunctioning all on its own. It's like the difference between being abused by a stranger and by your mother.

After these articles were written, evidence of a huge crater was found beneath the ice in Antarctica.

I don't know when or if they'll get core samples because it is buried about 1/2 mile below the ice. But those guys (Erwin, Ward, etc) have been puzzlingly silent about this discovery. I haven't seen a single comment by any of the big P-T authorities. What's with that?

2006-Oct-23, 01:05 AM
Interesting read. It seems that a 6 degree rise in temperature was enough to cause the methane trapped in the oceans to be suddenly released. Some estimates of current temperature rise suggest that much or more rise over the next 100 or so years. Makes one wonder.

I was wondering if the Earth has a natural feedback mechanism for keeping global warming from going out of control. When it gets warmer, plants grow more. If we get shorter winters, we'll have a lot more weeds, and forests might grow higher. These might take up some of the extra C02. Or so we can hope. That is, if developers stop bulldozing every forest they can see and if people stop killing plant growth with herbicides.

The reason why this mechanism didn't work in the Permian was, the sulfur dioxide from the volcanoes caused wicked acid rain that killed the plant life. By all accounts, the toxic chemicals pumped out of those volcanoes was thousands of times more than what our cars and smokestacks could churn out.

Or, at least this is the optimistic view.

2006-Oct-23, 01:14 AM
what about..... a huge oil/coal field was involved in a techtonic subduction and then all the carbon that was trapped there within was realeased as CO2 via volcanoes?

2006-Oct-23, 01:24 AM
I think the problem is that the evidence for either thoery is sketchy at best. Are we looking at cause or effect? Is it one or the other, or is it a combination? There is certainly evidence that something catastrophic happened (catastrophic meaning over a relatively short period) and it also seems that life had a difficult time recovering from it.

Keep in mind though, that whatever happened occurred a long, long time ago. There is not likely to be any specific evidence that will conclusively support one theory over the other.

2006-Oct-23, 04:49 AM
We know that plumes of upwelling magma exist in the mantle and last for a considerable period, the hawaii islands are formed of one such. When the plume upwells under a continental mass it burns its way though after building a molten reservoir. This reservoir fuels the vast expelled volume of the traps.

Heat rising from the core is going to concentrate in a plume, is the energy of an impact comparable to what is going on in the Core, or perhaps just enough to trigger anough instability in the mantle that any existing plume heads away?

Obviously the hope is that impact triggered events are theoretically preventable, a traps event might never be.