Space rocks keep fallin' on my head...

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Architeuthis
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Might the Mother of All Mass Extinctions have been caused by an asteroid impact? Not exactly a new idea, but there's some more chatter about it in this week's Science magazine. This BBC News article provides a brief summary, if you've neither the means nor the inclination to read the article in Science.

Personally, I prefer to blame the Permian-Triassic extinction on the formation of Pangea. But I'm a world-class ignoramus.
 

cthulhu77

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There is so much proof that a meteor could NOT have caused the extinction, that every time I read another article about it, I go crazy...why does there have to be a "one" reason...????? Maybe the dinosaurs drove bmw's and liked cold fusion technology...who knows?
good article though...thanks for the link!
Greg
 

tonmo

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Hiya Greg!

What's the evidence against a meteor causing the dinosaur extinction? (Reminds me of that classic Gary Larson cartoon with the dino's smoking: "The Real Reason Dinosaurs Became Extinct").

For clarity, this release talks about some "great dying" that supposedly occurred 250mya, as opposed to the dino event that is believed to occur 65mya.

90% of marine life!!
 

cthulhu77

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Too many large animals survived for it to have been a meteor induced wipeout...crocodiles especially (very dependant on UV light and warmth). The meteor theory is just too "pat"... the age of the dinosaurs was already in wind-down, and they didn't go extinct in a couple of years...they just died off as newer,more adaptable animals came along...that is the big danger in specializaton...ask any computer person in california ! There was a real wild theory out by a gentleman named Habermann (sic?) where the earth changes its axis as our wobble (3 degrees right now) escalates out of control every 70 million years or so...I guess if you want, you can always find enough "maybes" to fill any theory. Oh well...I'll stick with the Gary Larson verson!
Greg
 

tonmo

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fascinating! I've never read about these things (the crocodile observation, the axis wobbling theory)... I gotta get out more... (or stay in more?)
 

Phil

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I had not heard of the axis wobbling theory. Interesting, thanks Greg.

Extinction theory is a HUGE topic, people have written volumes on these events. But in short, there have been five previous major extinction events, excluding the current one underway. These were:

Late Ordovician extinction, 439mya
Late Devonian extinction, 362mya
End Permian extinction, 248mya
Late Triassic extinction, 205mya
End Cretaceous extinction, 65mya

There were other mass extinctions, but these are the ‘Top 5’, and of these the Permian was the biggest, with, as you say Tony, some estimates putting as high as 95% of all species becoming extinct. Though the Cretaceous extinction is, of course, the most famous due to the loss of the dinosaurs.

Ordovician Extinction, culminating 439mya. (22% marine families)
Cephalopods: Some nautiloid families, including the first nautiloid order the Ellesmeroceratina
Others: Some brachiopods, graptolites.
Possible cause: In the late Ordovician times the sea level dropped due to ice age and massive glaciation. Ice sheets spreading out from the poles would have lowered the sea level. Marine life on the continental shelves would have suffered vast habitat reduction. At the very end of the period, the opposite happened, the sea level suddenly rose polluting the continental shelves with oxygen-deficient deep water.

Devonian Extinction, culminating 362mya (21% marine families)
Cephalopods: Nautiloid families and the nautiloid order Discosorida. The obscure and short-lived Anarcestida and Clymeniida (two of the earliest ammonoid groups)
Others: Some forms of coral, 75% brachiopods, graptolites.
Possible cause: Poorly understood. Series of events, probably a drastic global cooling. Some evidence of meterorite impact; possible pollution of continental shelves by deep water.

Permian Extinction culminating 248mya (57% marine families, 95% total life)
Cephalopods: The nautiloid order Bactritida, the ammonoid goniatites and the ammonoid order Prolecanitida
Others: Trilobites. Devastating for terrestrial life.
Possible cause: Gradual event over 10 million years or so. Possible meteorite impact. All land masses locked together into Pangea causing overheating and vast climatic change, coupled with intense volcanic activity in Siberia causing dramatic rise in CO2 levels. Consequent alteration in oceanic currents. Drop in sea level at end of Permian due to glaciation with effects as above.

Triassic: Extinction culminating 205mya (20% marine families)
Cephalopods: Final orthoconic nautiloids, the ammonoid ceratites and the one of the earliest coleoid groups, the Aulacoceratida
Others: conodonts, many brachiopods, many forms of crinoid.
Possible cause: Climatic change causing increased rainfall in an otherwise arid period. This could have led to a change in surface temperature, and pH and salinity levels in the sea.

Cretaceous Extinction event 65mya (15% marine families, poss. 75% all families)
Cephalopods: the last few remaining families of ammonites and belemnites.
Others: Dinosaurs (dwindling anyway), sea reptiles, final pterosaurs, some land plants.
Possible cause: Meteorite impact, crater has been discovered in the Yucutan Peninsula, with layers of iridium, an element abundant in meteorites, present in clays the world over. Intense volcanic activity in the Deccan Traps in India, either caused by effects of the meteorite or India moving northwards sitting on top of a hot mantle plume. Blanketing of sky due to either/both events would have reduced plant photosynthesis causing a knock-on effect on terrestrial life and on the marine life via phytoplankton.

I totally agree, there may not be a single cause for these extinctions, often major extinctions seem to be a chain of interconnecting events. It goes without saying that although extinction events are terminally bad things for the species involved, they allow the survivors to diversify and fill vacant niches. For those survivors they are a wonderful opportunity.

Hope that is of some interest!
 

cthulhu77

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In "the lost world" by Crichton (not the movie, the book) he points out an interesting theory...that it was a naturally occurring behavioural problem that terminated most of the archosaurs (I am a firm believer that birds are archosaurs) especially the large species. I was at a party last week, and became involved in an animated discussion...if you read "fall of the roman empire" it sounds like you are reading the headlines of a current newspaper....creepy.
Now, where oh where have I placed my fiddle...
Greg
 

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Architeuthis
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tonmo said:
Hope that is of some interest!
I should say so! Thanks for the lesson! :notworth:
I'd also like to add my :notworth: .

Personally, I don't buy that meteorites have been solely responsible for some of these mass extinction events. I'm wondering if there's any good evidence of massive impacts that didn't correspond with large extinctions.
 

cthulhu77

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Rosie O'Donnel fell down yesterday, and no one is dead yet. I wonder if that qualifies. hmmm.
 

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