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Help!
I heard another news 'blurb' today (2/26/01) on CBS early morning news.
OK. My notes say--"Mass Extinction Before Dinosaurs--250 million years ago--Comet/Asteroid?--Hit so hard, volcanos erupted and lava covered the earth--95% of life became extinct--paved the way for dinosaurs.
That is all accurate (or what they said anyway!),
Becky

PS. I wonder how old this one is.
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"Mass Extinction Before Dinosaurs--250 million years ago--Comet/Asteroid?

Becky, this extinction has been known about for a long time. It was more devastating than the one 65 million years ago that wiped out the dinosaurs. This one left only minimal life. The theory that is being proposed now is that a crater found (can't remember where) was on the opposite side of the planet from a super plume of magma (sorta the precursor to a massive volcano). The shock waves from the impact traveled around the world, re-converging on the opposite side, right near the super plume. This triggered massive eruptions, as all the violent power was released at once. I think it was the latest Scientific American that had an article about this, or maybe National Geographic. I'll check when I get home.

I think (if I'm not getting it confused with another extinction) that there is a layer with some advanced fossils. Directly above is a layer with an unusual chemical makeup, consistent with volcanic debris, but also containing traces of rare elements. Above this line, there are many fewer advance fossils.

David
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The Dinosaur extinction was the K-C boundary, the cretacious-tertiary boundary between the mesozoic (age of reptiles) and the cenazoic (age of mamals). This was 65 mya. The P-T boundary was the mass extinction of 250 mya. This was the permian triasic boundary between the paleozoic (age of fish) and the mesozoic. Unless there was a new find, the last I was taught, this mass extinction was not caused by a comet, but was caused by the coalecence of the continents back into a one supercontinent stage (pangea) The enormouse environmental change wiped out 95% of the pre-existing biomass alowing for the next age to begin. The reptiles became dominant then because they occupied the niches that were freed by the death of anphibians who previously occupied those niches.

Note: A niche is a type of action or area in an ecosystem. i.e. eating fruit from a certain class of shrub is a niche.



When the next mass extinction took out the dinos' those niches became open for mamals to occupy. This leads back to the discussion on speciation where the mamals all evolve into the current ones via reproductive and/or social isolation brought about by geologic time. (MillionsYears).


Birds of a feather: The mamals in the canopy stop associating with the mamals on the forest floor. Neither of them associate with the mamals in the open plains, thus adaptation and selective pressure influence the developement of long necked mamals or trunked mamals, or mamals with strong tails etc.


Guiding with the light,
The Shepherd
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Becky,

CBS probably has a website. You may be able to get your info there.

Chris
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David,
Thanks, the fossil record sounds upside down if I read you right. Weird. This news we get make me wonder about the rest of it.
Becky
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Thanks, the fossil record sounds upside down if I read you right. Weird. This news we
get make me wonder about the rest of it.


Well, I guess on first glance it does look upside down. But a simpler explanation is that at one point, most life got wiped out. Only the very simple life forms survived. Since the same evidence has been found at multiple places, it is unlikely that something came along and flipped over the layers.

David
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OFH,
Thanks! I'm just getting all sorts of info today! So, these extinctions all began a new 'age'? Hmmm. Got to think on that. Becky
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"Thanks! I'm just getting all sorts of info today!"

Your welcome! :)sss


"So, these extinctions all began a new 'age'? Hmmm. Got to think on that."

Not quite, mass extinctions do not begin the new ages, they occur because after the new age has begun. They are a marker of when the new age started. They occur, because planetary conditions are so different from what they just were that many thing just can't adapt and/or survive. When a mass extinction is noticed in the geologic record, one asks "Why did all these species go extinct?" The usual hypothesis are:

Comet/meteor
Huge Tectonic event (continental colisions or seperations)
Sudden global climate change


After mass extinctions, an explosion of new species takes place. I.E. reptiles after the P-T, mamals after the k-t

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Chris,
I did think of looking for the article an the 'volcanic
extinction' myself---but then I thought of Amy and dumped it on her! I was pleasantly suprised to see the guys fill in for her. I will look myself if I ever get caught up!
Becky

PS.Why not talk about the other, newer dating methods?
I sure could use the education and I read of one the other day and can't remember a thing about it except it's more accurate(so they said).
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David,
OK I'll go with your simpler idea, but it's still weird.

Becky
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