Freethought & Rationalism Archive

Claudia · 05-22-2003, 07:26 AM

there have been several hypothesis to explain the big extinctions, among which the most famous (not the biggest) is the one occuring between Cretaceous and Tertiary (K/T).
I have heard for hypothesis:

-variation of sea level (don't remember the name of who propose this)

-apparition of new volcanic hot spot -> Volcanic Trapps expansion (Vincent Courtillot) for K/T extinction, Deccan Trapps

-Big impact of space object (Luis Alvarez). For K/T extinction, Chicxulub crater. Has become the most popular explanation for K/T extinction.

I have read recently an interview of Vincent Courtillot stating that the conflicting propositions are progressively reaching an agreement: he agrees that for K/T extinction, Chicxulub impact was probably an important factor, and he says that Alvarez agree that it is probably the only extinction when an impact had influence.

Does some of you have informations on the latest state of theart about this subject? And on explanation of other mass extinctions?

ps418 · 05-22-2003, 08:09 AM

The K/T is the only one of the 5 mass extinctions conclusively tied to an impact event. I wrote a mini-review on the Permian-Triassic extinction for my web site that discusses hypotheses relating to that extinction. It has some crappy grammer and could be better organized, but there is some good info there too:

click here

Patrick

Jack the Bodiless · 05-22-2003, 08:44 AM

IIRC, there is a current theory that the Deccan Traps were caused by the Chixtulub impact. Allowing for continental drift, India was on the opposite side of the planet from Chixtulub at the time: impact shock waves would have converged on that point.

Presumably, if the same thing happened in the Permian (Siberian Traps), the impact site would have been in the deep ocean opposite Pangaea and would likely have been subducted by now, unless it's still in the Pacific.

ps418 · 05-22-2003, 09:24 AM

Quote:

Originally posted by Jack the Bodiless
IIRC, there is a current theory that the Deccan Traps were caused by the Chixtulub impact. Allowing for continental drift, India was on the opposite side of the planet from Chixtulub at the time: impact shock waves would have converged on that point.

That was a tempting theory at one point, but now it can be ruled out, because we know that the Deccan Traps had already begun to form when the Chixulub impact occurred. The Iridium anamoly that is a worldwide isochronous marker of the impact event is also found within the Deccan Traps, in an "intertrap" sedimentary layer denoted ITIII, between the third (FIII) and fourth (FIV) basalt flows. The three lower flows possess normal magnetism, and are placed within the latest Cretaceous normal chron C30N, while FIV is revesely magnetized, and placed within chron C29R. This sediment or intertrappean layer was formed after the extrusion of FIII, but before extrusion of FIV, which have been Ar-40/Ar-39 dated at 65.5+/-0.7 and 65.4+/-0.7my respectively. Thus, Deccan volcanism was well under way prior to the impact (Bhandari, N., Shukla, P.N. et al. 1995. Impact Did not Trigger Deccan Volcanism: Evidence from Anjar K/T Boundary Intertrappean Sediments. Geophysical Research Letters 22: 433-436). Theoretically, though, you could invoke a second, pre-Chixulub impact to initiate the Deccan volcanism.

Patrick

Claudia · 05-22-2003, 09:41 AM

I have read (not in a scientific paper, but in a review of Courtillot's book "Evolutionary Catastrophes: the Science of Mass Extinction" that: "In fact, the famous KT iridium-signature has recently been identified in Deccan interflow sediments."
http://www.sfsite.com/05a/ec80.htm
Has it been confirmed? if yes, is it consistent with

Quote:

there is a current theory that the Deccan Traps were caused by the Chixtulub impact. Allowing for continental drift, India was on the opposite side of the planet from Chixtulub at the time: impact shock waves would have converged on that point.

[edit]Thanks ps418, you answered my question before I asked it!

[/edit]

Sauron · 05-22-2003, 08:33 PM

Patrick, perhaps I could trouble you to help here?

I saw a PBS show recently that discussed the Permian extinction. Briefly, it attributed a 1-2 degree rise in temperature to the global warming effect of the meteor impact.

It then discussed Siberian lava traps, and a release of another gas (can't remember which one) that further raised the temperature 1-2 degrees. The combined effect of both events created the Permian extinction. The show estimated that it took 10 million years, from beginning to end. Apologies if I don't have the the explanation 100% correct - feel free to fix it up.

Here's my question - with an extinction event caused by a meteor impact of this kind, I can't see how life would live past the first five years afterwards, much less for 5 or 10 million years. After the dust particles obscured the sun for a year or two, I would imagine that the foundation food sources would all be gone. It seems that if plants and plant-like life (algae, plankton, etc.) are the foundation of life, then any even that threatens them would send a deadly shock wave up the food chain immediately.

Are there any explanations for the Permian extinction that address my question?

Thank you.

Claudia · 05-23-2003, 12:57 AM

Which meteor for the Permian extinction?
Patrick told that

Quote:

The K/T is the only one of the 5 mass extinctions conclusively tied to an impact event.

ps418 · 05-23-2003, 07:14 AM

Quote:

Originally posted by Sauron
Patrick, perhaps I could trouble you to help here?

Sure, and its no trouble.

Quote:

I saw a PBS show recently that discussed the Permian extinction. Briefly, it attributed a 1-2 degree rise in temperature to the global warming effect of the meteor impact.

It then discussed Siberian lava traps, and a release of another gas (can't remember which one) that further raised the temperature 1-2 degrees. The combined effect of both events created the Permian extinction. The show estimated that it took 10 million years, from beginning to end. Apologies if I don't have the the explanation 100% correct - feel free to fix it up.

You're thinking of CO2 and SO2, both of which are greenhouse gasses and both of which are released with volcanism. These gasses play a major role in the currently most-widely-accepted explanation of the P-Tr event -- they initiate warming, which passes a threshold and destabilizes methane clathrates in the ocean, which releases methane into the atmosphere, which causes further warming.

Quote:

Here's my question - with an extinction event caused by a meteor impact of this kind, I can't see how life would live past the first five years afterwards, much less for 5 or 10 million years. After the dust particles obscured the sun for a year or two, I would imagine that the foundation food sources would all be gone. It seems that if plants and plant-like life (algae, plankton, etc.) are the foundation of life, then any even that threatens them would send a deadly shock wave up the food chain immediately.
[/B]

As I said above, the evidence for a P-Tr impact is pretty scant. Not totally nonexistent, but very scant indeed compared to the unequivocal and globally distributed evidence for a major K-T impact. Greg Retallack reported finding one-or two shock-metamorphosed zircons from a P-Tr boundary section in Antarctica, yet these are considered equivocal.

Becker et al (2001) argued for an impact event based on the isotopic ratios of nobles gasses trapped in fullerene molecules (which are something like cages) from two P-Tr boundary sections: one in Meishan, China, and one in Sasayama, Japan (one in B�kk mountains in Northern Hungary was tested, but not ET signature was detected). Purportedly the isotopic ratios of helium and argon are consistent with the impact of a chondritic meteorite, but not likely to be derived from a terrestrial source. This phenomena has also been associated with the K-T.

However, the existence of an noble gas ET signature at both the Chinese and Japanese P-Tr sections was immediately questioned (Farley et al, 2001). In the Chinese section, no fullerence ET signature could be detected, despite testing more samples and from more levels than Becker et al, and Isozaki pointed out that the Beckers Japanese section was actually well below the P-Tr boundary.

So, all in all, I think the evidence for an impact is pretty scant.

But to answer your question -- how could any animals survive if the sun was obscured for 1-2 years? The answer is that if the sun were totally obscured for 1-2 years, they couldn't. However, some animals would easily be able to survive as long as there was some sunlight. I dont how long dust can remain in the atmosphere, but I dont think it possible that enough dust could remain in the atmosphere for 1-2 years to totally obscure the sun. I imagine a few dozen very dark days and alot of gray days after that. Plus, keep in mind that primary productivity almost did shut down across the P-Tr, judging from the remarkable P-Tr stratigraphic 'dead zone'!

Refs

Becker, Luann, Robert J. Poreda, Andrew G. Hunt, Theodore E. Bunch, and Michael Rampino (2001) Impact event at the Permian-Triassic boundary: evidence from extraterrestrial noble gases in fullerenes. Science, vol. 291, p. 1530-1533.

Farley, K. A., Mukhopadhyay, S., Isozaki, Y., Becker, L., Poreda, R. J. (2001). An Extraterrestrial Impact at the Permian-Triassic Boundary?. Science 293: 2343a-2343.

Patrick

ps418 · 05-23-2003, 07:20 AM

Sauron,

Regarding volcanism, warming, and methane release at the P-Tr, this is from the little mini-review I linked to above.

Quote:

A Possible Explanation?

In contrast to the K-T extinction, the cause(s) of the P-Tr extinction are not well understood. Bolide impact has been proposed, but the evidence for this is ambiguous, especially compared to the massive and unequivocal evidence for a major bolide impact at the K-T boundary. There is some indication, however, that large-scale volcanism may have played a role.

Several of the classic P-Tr sections in South China are capped by 3-6cm thick altered volcanic ash layers containing bypyramidal quartz, melt spherules, glass shards and isotopic ratios typical of siliciclastic rather than basaltic volcanism. The volume of these ash layers is estimated to be about 1000km3, equal to the volume of water flowing through the Yangtze River in one year (Zhou and Kyte, 1988). Analysis of 40Ar/39Ar data from two tuffs in southern China yield dates of 250.0 +/- 0.2 million years ago for the Permian-Triassic boundary, which is comparable to the inception of main stage Siberian volcanism at 250.0 +/- 0.3 million years ago (Renne et al., 1995). This is consistent with biostratigraphic data -- the basal tuffs of the Siberian volcanics are interbedded with midle late Permian fossils (Kozur, 1998).

The P-Tr boundary occurred at roughly the same time as the extrusion of the largest known Phanerozoic flood basalts, the Siberian Traps. Laser-heating 40Ar/39Ar plateau dating indicates that the bulk of these basalts was erupted over an extremely short time interval at mean eruption rates greater than 1.3 cubic kilometers per year (Renne et al. 1991). These volcanic flows presently cover an area of 337,000 square kilometers. They are estimated to have a volume of about 1.6-2.5 (estimates vary) million cubic kilometers of solidified basaltic lava. Spread evenly over the earth's entire surface, this volume of lava would produce a layer 10 feet thick.

Volcanism on this scale would release massive amounts of CO2 and SO2, as well as aerosols that would block a significant amount of sunlight. Initially, this would result in cooling. However, the SO2 would leave the atmosphere in the form of acidic rain, and within a few months most of the particulate matter would be gone from the atmosphere. This may have played some role in the extinctions on land. However, the CO2 would remain, and this would result in warming. Assuming a volume of 2 x 10^6 km3 of basalt, and release of 5 x 10^12g CO2 per km3 of basalt, then the Siberian Traps would have released 1 x 10^19g of CO2 (Wignall, 2001).

Warming as a result of volcanic CO2 may have resulted in the dissociation of methane hydrates, and the development of anoxic conditions in the oceans. Warming promotes anoxic is two ways. First, the solubility of O2 in water decreases with increasing water temperature. Second, warming can promote anoxia if the equator-to-pole temperature gradient is weakened, since this would weaken oceanic circulation (Hallam and Wignall, 1997, p. 141). Finally, warming via volcanic CO2 may have caused the dissociation of gas hydrates, which would cause even more warming.

Study of other mass extinction intervals shows that several are correlated with both flood basalts and anoxic episodes. Of 11 major flood basalts, 7 coincide with some form of extinction episode (Wignall, 2001). 2 of these extinction events, the Toarcian (Jurassic) and latest Paleocene, are similar in many ways to the P-Tr extinction. The Toarcian extinction occurred at the same time as the Karoo-Ferrar basalts in South Africa and Antarctica were extruded (183 +/-1Ma), and the late Paleocene 'event' occurred at the same time as the extrusion of the Brito-Arctic flood basalts (55Ma). Like the end-Permian, both events are associated with warming, marine anoxia, major carbon isotope excursions, and the preferential extinction of benthic marine organisms (Wignall, 2001). Methane release has also been proposed for both events (e.g. Hesselbo et al., 2000; Katz et al., 1999).

Patrick

MrDarwin · 05-23-2003, 07:39 AM

Quote:

Originally posted by Sauron
Here's my question - with an extinction event caused by a meteor impact of this kind, I can't see how life would live past the first five years afterwards, much less for 5 or 10 million years. After the dust particles obscured the sun for a year or two, I would imagine that the foundation food sources would all be gone. It seems that if plants and plant-like life (algae, plankton, etc.) are the foundation of life, then any even that threatens them would send a deadly shock wave up the food chain immediately.

I can't comment on the Permian extinction, which as Patrick says is less understood, and seems to be a very different event from the K/T extinction event. But many plants can survive for years as seeds or spores (sometimes even as roots or other dormant structures) in the soil, as any gardener or farmer can attest! Many of these species are specifically adapted to rapidly colonize areas disturbed by landslides, hurricanes, fires, etc. once the dominant vegetation is removed. Furthermore, many plants are tough and weedy and can grow and reproduce rapidly under many different conditions, and others are forest understory species, specifically adapted to low light and might quickly become the dominant vegetation in a world that had diminished light and had most of its forests destroyed.

Regarding animals, anything that is a scavenger would do quite well in the days or years following such an event, when other animals are dying off in large numbers and leaving their corpses lying around! I imagine fungi (really just another kind of scavenger) would also do quite well with lots of dead vegetation lying around.

In other words, what is devastating to one species might be a very, very good thing for another.

I was recently working on a paper reviewing some of the recent molecular phylogenies of angiosperms (flowering plants) and two interesting results are coming out of such studies: first, that several major groups of plants are older than previously suspected, and second, that the major radiations of these groups began shortly after the KT extinction. I expect to see more papers in the future dealing with this.

05-22-2003, 07:26 AM	#1
Claudia Senior Member Join Date: Apr 2001 Location: France Posts: 715	Extinctions: Volcanic Trapps, Meteorits, or other? there have been several hypothesis to explain the big extinctions, among which the most famous (not the biggest) is the one occuring between Cretaceous and Tertiary (K/T). I have heard for hypothesis: -variation of sea level (don't remember the name of who propose this) -apparition of new volcanic hot spot -> Volcanic Trapps expansion (Vincent Courtillot) for K/T extinction, Deccan Trapps -Big impact of space object (Luis Alvarez). For K/T extinction, Chicxulub crater. Has become the most popular explanation for K/T extinction. I have read recently an interview of Vincent Courtillot stating that the conflicting propositions are progressively reaching an agreement: he agrees that for K/T extinction, Chicxulub impact was probably an important factor, and he says that Alvarez agree that it is probably the only extinction when an impact had influence. Does some of you have informations on the latest state of theart about this subject? And on explanation of other mass extinctions?

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05-22-2003, 08:09 AM	#2
ps418 Veteran Member Join Date: Mar 2001 Location: Louisville, KY, USA Posts: 1,840	The K/T is the only one of the 5 mass extinctions conclusively tied to an impact event. I wrote a mini-review on the Permian-Triassic extinction for my web site that discusses hypotheses relating to that extinction. It has some crappy grammer and could be better organized, but there is some good info there too: click here Patrick

05-22-2003, 08:44 AM	#3
Jack the Bodiless Veteran Member Join Date: Feb 2001 Location: UK Posts: 5,815	IIRC, there is a current theory that the Deccan Traps were caused by the Chixtulub impact. Allowing for continental drift, India was on the opposite side of the planet from Chixtulub at the time: impact shock waves would have converged on that point. Presumably, if the same thing happened in the Permian (Siberian Traps), the impact site would have been in the deep ocean opposite Pangaea and would likely have been subducted by now, unless it's still in the Pacific.

05-22-2003, 08:33 PM	#6
Sauron Veteran Member Join Date: Jan 2001 Location: In the dark places of the world Posts: 8,093	Patrick, perhaps I could trouble you to help here? I saw a PBS show recently that discussed the Permian extinction. Briefly, it attributed a 1-2 degree rise in temperature to the global warming effect of the meteor impact. It then discussed Siberian lava traps, and a release of another gas (can't remember which one) that further raised the temperature 1-2 degrees. The combined effect of both events created the Permian extinction. The show estimated that it took 10 million years, from beginning to end. Apologies if I don't have the the explanation 100% correct - feel free to fix it up. Here's my question - with an extinction event caused by a meteor impact of this kind, I can't see how life would live past the first five years afterwards, much less for 5 or 10 million years. After the dust particles obscured the sun for a year or two, I would imagine that the foundation food sources would all be gone. It seems that if plants and plant-like life (algae, plankton, etc.) are the foundation of life, then any even that threatens them would send a deadly shock wave up the food chain immediately. Are there any explanations for the Permian extinction that address my question? Thank you.

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