News item about Ordovician extinction

Phil

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#4
Thanks Melissa,

Well, I'd always thought the Ordovician extinction was due to a global ice-age and widespread glaciation. I wonder if the two theories have been combined somehow? Maybe the gamma-ray burst could have triggered the ice-age in some way? Must try and find the whole text.

It's always fun to think of 'what if' scenarios. Imagine if there had been no Ordovician extinction? Would the giant orthoconic nautiloids have survived for much longer? Would the ammonoids have appeared? Hmm........
 

spartacus

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Phil said:
Would the giant orthoconic nautiloids have survived for much longer? Would the ammonoids have appeared? Hmm........
......& without the giant orthoconic nautiloids would there have been "Cornettos" ?

Keef
 

monty

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#6
Phil said:
Well, I'd always thought the Ordovician extinction was due to a global ice-age and widespread glaciation. I wonder if the two theories have been combined somehow? Maybe the gamma-ray burst could have triggered the ice-age in some way? Must try and find the whole text.
Here's the full text:

http://xxx.arxiv.org/abs/astro-ph/0309415

This is the URL mentioned in the NASA press release. It has pretty pictures:

http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html

the first author's web page is

http://kusmos.phsx.ku.edu/~melott/Melott.html

It sounds like they believe that UV exposure caused the extinction, and there doesn't appear to be any notion of a correlated ice age (although I only read the conclusion section in detail).
 

Architeuthoceras

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From the NASA link

Dr. Bruce Lieberman, a paleontologist at the University of Kansas, originated the idea that a gamma-ray burst specifically could have caused the great Ordovician extinction, 200 million years before the dinosaurs. An ice age is thought to have caused this extinction. But a gamma-ray burst could have caused a fast die-out early on and also could have triggered the significant drop in surface temperature on Earth.
 

monty

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Architeuthoceras said:
From the NASA link
oops. I should've read a little more closely before posting... had to finish my taxes, though...:oops:
 

Fujisawas Sake

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Good paper, good hypothesis.

To piggyback on this paper, this is related to Carl Sagan's "nuclear winter" theory. In the book Cosmos, Sagan proposed that the dust scattered by high-yeild thermonuclear devices would lead to global cooling and a corresponding ice age. Now, while the dust by itself would remain for some time, Sagan went on to describe the conversion of atmospheric nitrogen into ozone-depleting oxides of Nitrogen (NOx) which would further scatter light and cool the Earth even more. The situation given here is less extreme (no nuclear bombs), but a nasty blow to a world dependent on photosynthesis and where a majority of your life is shallow water planktonic-dependent. We're talking a massive amount of devastation in a very short (geologically-speaking) amount of time.

This is a good hypothesis. Hmm... if it were within a 6000 ly distance, that would put it relatively in our neighborhood. Such a burst might be traced back to a supermassive start collapsing into a neutron star or black hole, both of which can be detected, even this long after the initial event. As far as local black holes are considered, the only one of which I know is Cygnus X-1, but that's a cool 11,000 light years from us. Neutron stars exist in decent numbers. But I'm only an amateur astronomer, so what do I know?

Its a good hypothesis. Any alternatives out there?

Thanks for the food for thought.

John
 
#11
Now isn't the problem with a gamma-ray burst that it only affects one hemisphere, namely the one pointed towards the burst at the time the shockwave arrives?*

Let's say one arrived right now from Polaris, and cooked the northern hemisphere... the Indonesian, Kiwis and Aussies would get their chance to rule the world ;)

*Edit - now I read the paper I see the NOx smog, and depleted ozone, propagate to the other hemisphere after the bust and thus become global in extent. OK, it could have happened. But until they find a radioisotopic signature of the event it's going to be rather "what-if" ish isn' it?
 

Fujisawas Sake

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Actually, I don't think you would find a radio-active decay signature here because the culprits were cosmic rays and UV photons, which would have HEAVILY been blocked by the Van Allen belts and Ozone. Also, the NOx's woudl have broken down in a few years, not leaving a trace a trace of "radiation" (nuclear decay) per se. The evidence might be unlockable in deep ice cores (if such ancient ice cores exist) or in some ancient atmospheric nitrogen sinks.

And like I said, this paper is merely a hypothesis for now... The testing is a bit out of reach of our technology at the moment.

John
 

Phil

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There may be a potential problem with this theory that the Ordovician extinction was not limited to a single event 445 million years ago, but was supposed to have happened to two phases, at the beginning and end of the glacial event. The onset of glaciation led to a massive sea level drop, maybe as much as 100m, causing changes to oceanic circulation patterns and widespread disruption to marine communities. The second burst of extinction came at the end with the return to warmer conditions marking the beginning of the Silurian. The second glacial period at the end of the Ordovician may have lasted around 500,000 years. The problem here is that apparantly most of the extinctions took place amongst deep water forms (trilobites, brachiopods) which is not really what one would expect for a gamma-ray burst.

Here's an interesting paper on the event for anyone interested:

The Late Ordovician Mass Extinction by Peter Sheehan (2001)

As for cephalopods, Sheehan records:

Cephalopods: Nautiloids experienced severe extinction, with the most important orders declining to only a few genera (Crick 1990). Of eight Ordovician orders,(a) one became extinct, (b) three survived and by the Wenlock had regained or surpassed their Ordovician diversity, and (c) four survived but never regained their prior diversity (House 1988). Unlike most other groups, the post extinction faunas were highly endemic, which suggests that the extinction may have been concentrated in the more cosmopolitan taxa (Crick 1990).
I'm afraid that ice-cores are out for such an ancient period, FJ. Maybe someone could do work on fossilised plankton though?
 

Fujisawas Sake

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Phil,

Well, the burst would probably not have caused everything singlehandedly. This theory is a bit hung up on that idea, and I'm not too sold on it myself. Its like the death of the dinosaurs; they seemed to be on their way out anyway, either evolving to diferent forms or vanishing altogether. The comet or asteroid was probably the final nail in their coffin as the Order Dinosauria. I have the feeling that there was more than meets the fossil here. I get the feeling that most mass extinctions are caused by "a series of unfortunate events" (with all due respect to Lemony Snickett) which come together in a mass harmonic convergence of 'sucktitude'. :wink:

The burster idea is good, but I would hardly say perfect. AND, as much as I tend to be a little cynical in my scientific sense, it looks good as the prelude for a grant proposal to get the money to build a kicka$$ space probe to detect them. Sorry to say it like that, but with science not taking a front-seat in this country, you need to find money any where you can... :hmm:

Thanks for the link.

John
 

DHyslop

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#15
Fujisawas Sake said:
Phil,

Its like the death of the dinosaurs; they seemed to be on their way out anyway, either evolving to diferent forms or vanishing altogether. The comet or asteroid was probably the final nail in their coffin as the Order Dinosauria.

John

Signor/Lipps :p

Dan
 

spartacus

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Fujisawas Sake said:
it looks good as the prelude for a grant proposal to get the money to build a kicka$$ space probe to detect them. Sorry to say it like that, but with science not taking a front-seat in this country, you need to find money any where you can... :hmm:
If someone's after funding for a probe, they've missed the boat ! :sad:
The NASA lead Swift mission is detecting GRB's as I type. I was going to poach some of it's "coded mask" technology for my "Super Suture Searcher" but I had to pull the plug due to a lack of investors & aptitude !

Keef
 

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