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Old 04-17-2014, 04:17 AM
 
Location: Wasilla, Alaska
17,850 posts, read 19,595,646 times
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The Permian/Triassic extinction event was the greatest extinction event since complex life formed some 540 million years ago. Approximately 96% of all marine life, and 70% of all terrestrial life disappeared.

Contrary to popular belief, there was not just one extinction event. Approximately 270 million years ago there was an extinction event greater than the famous Cretaceous/Tertiary Extinction Event 65.5 million years ago. After another 9 to 10 million years (~260 million years ago) another extinction event occurred, and 9 to 10 million years after that the extinction event that ended the Permian Period.

Yet there is no satisfactory explanation for what caused these events. So I thought I would create a thread and open the discussion as to what might explain these three Permian extinction events.

In order to have an inkling of what was happening during that time we need some data. The atmospheric composition is derived by determining the ratio between different isotopes of the carbon molecule.

Atmospheric Oxygen
The oxygen content of our atmosphere has pretty much leveled out at 21.2% for the last ~40 million years. However, the oxygen content was much lower from the Cambrian to the beginning of the Devonian, ranging from 15% to 18%. Then, gradually, over a period of ~100 million years the oxygen content began increasing. This also corresponds with plants on land beginning to thrive during the Devonian and peaking at the end of the Carboniferous. The oxygen content peaked at the end of the Carboniferous Period at ~35%, and then over a period of ~50 million years dropped to ~15% by the end of the Permian.

There is a ~3% peak increase in the oxygen content during the Triassic, but it does not start to climb again until the Triassic/Jurassic boundary, some 220 million years ago. This also corresponds with the break-up of the super-continent Pangaea.



Atmospheric Carbon Dioxide
The carbon dioxide levels, on the other hand, peaked and then began declining during the Cambrian, and with the exception of a couple of spikes during the Ordovician and Devonian, continued to decline until it reached its lowest level at the end of the Carboniferous. There is also evidence that just before the end of the Carboniferous there was an ice age that lasted into the Permian.

It should also be noted that at the Permian/Triassic boundary, there is no carbon layer in the Karoo, in South Africa, which is where most Permian strata is studied.

Surface Temperature
During the Cambrian and Ordovician the surface temperature was ~24C, then quite suddenly (less than 10 million years) the temperature dropped by 8C to 10C, starting the Silurian Ice Age. Just as suddenly the surface temperature rebounded back to its original Cambrian/Ordovician levels. At the beginning of the Carboniferous the temperature drops by 2C to 3C, and then plunges another 6C to 8C.



During the Permian, after the Carboniferous/Permian ice age ended, the temperature shoots up again to between 21C and 22C around 270 million years ago. Then at the Permian/Triassic boundary, 250 million years ago the temperature spikes again to ~30C. Some have even placed the mean surface temperature even higher.



Needless to say, it got very warm by the end of the Permian. So warm that some have described equatorial and tropical regions of the planet as a "dead zone." No plant or animal life according to the fossil record in those regions.

Land Mass Distribution
Besides knowing what was going on with the atmosphere and surface temperatures, it would also help to see how the land mass was distributed around the planet at the time.



By the end of the Carboniferous there were two main continents; Gondwanaland and Laurasia. And they are on a collision course. What is now Brazil was located at the south pole. The smaller Eruamerica continent was at the equator, surrounded by shallow seas but still connected the rest of Gondwanaland (Africa, South America, Madagascar, India, Australia, and Antarctica).



Gondwanaland collides further with the Euramerica continent, and closes the gap with Laurasia even more. This also corresponds to when the Carboniferous/Permian ice age ends and surface temperature reach 22C to 23C.


During the beginning of the Triassic the super-continent of Pangaea is fully formed. Although it will not stay that way for long. About 20 million years later, at the Triassic/Jurassic boundary, Pangaea breaks up.

Proposed Explanations
There has been a lot of debate as to what caused the Permian/Triassic extinction event.

Some have blamed the volcanic activity from the Siberian Traps, which started to erupt as Pangaea was being created some 248 million years ago. However, that does not fit our observations of volcanic activity. First and foremost, in absolutely every case volcanic activity lowers the surface temperature of the planet temporarily. In no case has volcanic activity ever been observed increasing surface temperatures. Second, volcanic activity typically puts up copious amounts of sulfur dioxide, carbon dioxide, methane, water vapor, and other gases into the atmosphere. Yet the geological record shows only a gradual increase in carbon dioxide over a 50 million year period. Also, the Permian extinction events start 32 million years before, and finish 2 to 3 million years before the Siberian Traps began erupting.

Then there are some who believe the Permian/Triassic extinction event was the result of a meteorite impact. Yet they are not finding an impact crater, or any iridium, shocked-quartz, or micro-diamonds in the rock strata from that period.

While others have blamed anoxic oceans and the mixing of the seas as the cause of Permian/Triassic extinction event. Personally, I tend to favor this explanation because it best fits the data and what was happening to the planet at the time. However, it is also flawed because it does not explain why 70% of the terrestrial life died at the same time. Additionally, a recent study using molybdenum isotope ratios instead of carbon isotope ratios has determined that the northwest continental shelf of Pangea underwent mass extinction under oxic conditions, and therefore anoxia could not be the cause of the Permian/Triassic extinction event.

So we are pretty much back to square one: We still do not know what caused the greatest extinction event in the history of life on Earth.

Does anyone want to try to tie all the data together to come up with a plausible explanation?

_____________________________
References:

Last edited by Glitch; 04-17-2014 at 04:47 AM..
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Old 04-18-2014, 07:27 PM
Zot
 
Location: 3rd rock from a nearby star
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Those were the days, we were young and experimenting with all sorts of fauna types. Things are evolving so slowly today.
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Old 04-19-2014, 04:22 AM
 
Location: Wasilla, Alaska
17,850 posts, read 19,595,646 times
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Quote:
Originally Posted by Zot View Post
Those were the days, we were young and experimenting with all sorts of fauna types. Things are evolving so slowly today.
It is very likely that the life that formed during the Devonian and Carboniferous, when the oxygen content of the atmosphere was the highest it has ever been, could not survive the plunge oxygen took during the Permian. Those life-forms would have been accustom to 30% or 35% oxygen levels, and by the end of the Permian the atmospheric oxygen content dropped to 15%. If you cut our current oxygen levels in half or more, I would imagine that we would have difficulty surviving as well.

While there is an extinction event as the Carboniferous ice age began, it is relatively small when compared to other extinction events. The first major extinction event occurred just after that ice age ended. The surface temperature shot back up to where it was before the ice age began around 270 million years ago. Then as temperatures continued to climb to ~30C and higher, more species began dieing off peaking at ~250 million years ago.

Something, which has yet to be explained, caused surface temperatures to soar, and it was not carbon dioxide. Carbon dioxide levels during the Permian were lower than they are today and they did not begin to rise until the Siberian Traps started erupting 248 million years ago - after the Permian extinction event.

I think the key lies with the temperature. If plants began dieing off beginning at the end of the Carboniferous, it could explain the gradual decline of the oxygen in the atmosphere. It should have also made the extinction of certain species more gradual since this happened over a 50 million year period. However, the fossil record shows that most species survived the Carboniferous and Permian, until the last final three extinction events 270, 260, and 250 million years ago.

Perhaps there was some sort of massive coronal mass emission from the Sun that occurred 9 to 10 million years apart, as an explanation for the sudden increase in surface temperature, but that seems to stretch credulity. Why has it not happened before, or since? We have a fairly good idea of how life progressed over the last 500 million years, and the Permian extinction event stands out like a sore thumb.

Something caused the planet to heat up drastically, more than double today's mean surface temperature, and the answer does not appear to be in the content of the atmosphere at the time.

Last edited by Glitch; 04-19-2014 at 04:31 AM..
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Old 04-19-2014, 04:22 PM
Zot
 
Location: 3rd rock from a nearby star
468 posts, read 559,286 times
Reputation: 745
Cool Walk the dinosaur

Quote:
Originally Posted by Glitch View Post
It is very likely that the life that formed during the Devonian and Carboniferous, when the oxygen content of the atmosphere was the highest it has ever been, could not survive the plunge oxygen took during the Permian. Those life-forms would have been accustom to 30% or 35% oxygen levels, and by the end of the Permian the atmospheric oxygen content dropped to 15%.
I'd like higher levels of oxygen personally, it seems with age, my body isn't processing oxygen into my blood quite as efficiently as when younger.

The best I can do for now is HVAC with high filtration and carbon filters. One day, maybe a whole home oxygenation system will exist at an affordable price. Then spontaneous evolutionary experimentation in my new micro high oxygen environment can begin. It could be interesting.
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Old 04-20-2014, 09:12 PM
 
Location: Wasilla, Alaska
17,850 posts, read 19,595,646 times
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While I still have absolutely no idea why the mean surface temperature soared to ~30C or higher 250-251 million years ago, it just occurred to me that the erupting Siberian Traps (248 million years ago) may explain why shortly after reaching its peak 250 million years ago the temperature drops by ~5C.

A very large eruption, or a prolonged eruption, could very well have caused the planet to cool slightly after the Permian/Triassic extinction event. In a sense, the erupting Siberian Traps could have made the extinction event less severe by cooling off the planet, slightly. Assuming the reason for the extinction event in the first place was due to the excessive heat.
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Old 05-05-2014, 10:05 AM
 
Location: where you sip the tea of the breasts of the spinsters of Utica
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Supernova? Near-Earth supernova - Wikipedia, the free encyclopedia

Gamma Ray Bursts?
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Old 05-05-2014, 11:54 AM
 
Location: Wasilla, Alaska
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Originally Posted by Woof View Post
I certainly would not rule out the possibility of either.

According to a paper written a couple years ago, they suspect that 1,239/1,240 years ago the Earth was hit by a relatively close gamma-ray burst. The evidence they have for this is a sharp spike in the 14 carbon isotope detected in the tree rings.

A Galactic short gamma-ray burst as cause for the 14C peak in AD 774/5 - arXiv : 1211.2584v1 [PDF]

I do not know if they are able to make such a distinction in the geological record. Especially when we are talking 250-270 million years ago.

A massive gamma-ray burst from either a relatively nearby supernova or other gamma-ray source (such as two colliding neutron stars, for example) could have wiped out a large portion of our ozone layer, causing UV radiation from the sun to have an even more deadly effect. But that should have affected terrestrial life more than marine life. Unless, it was just a precursor of what was to come. For example, a relatively nearby supernova or gamma-ray source may not have directly caused the extinction event, but rather created the conditions for the extinction event to occur. Such as increasing the mean surface temperature of the planet, which in turn caused the mass extinction.

I do not know what a relatively nearby supernova or gamma-ray source may do to the atmosphere or temperature of the planet. Which is why I would not rule out the possibility. I cannot think of a plausible Earth-based event that can explain a sudden spike in the mean surface temperature. Which leads me to believe that the culprit may indeed have been extra-terrestrial.
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