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Re: Scientists conclude asteroid, not volcanoes, wiped out dinosaurs



"Dora Smith" <villandra@austin.rr.com>

> How do we know how
> abrupt were the extinctions?
> Were they really all that abrupt?

Good question.  It's still unknown.
In terms of geological time, the exinctions were unquestionably instantaneous.  
However, resolving geological time down to hundreds of years or less is simply 
not possible when studying events 65 million years ago.

In terms of human-viewed time, the extinctions could have occurred over a 
period of a few decades.  Maybe up to a hundred years.

You might want to read this paper:

Williams, M.E. 1994. Catastrophic versus noncatastrophic extinction of the 
dinosaurs: Testing, falsifiability, and the burdon of proof. Journal of 
Paleontology 68: 183-190.


> Were the Deccan trap
> eruptions like the Siberian
> traps, or were they just
> a series of super volcanoes?

They were plateau-style fissure eruptions, similar to the Siberian flows and 
the Columbia River flows in the U.S.  There are many of them.


> I'm left vague on how
> much toxic gas was put
> out by either event.


Considering the volume of lava produced, probably a butt-load.  Butt, 
(err....but,) it was expelled over millions of years, not instantaneously, so 
the noxious gasses had time to dissipate between eruptions, which were very 
infrequent.  I doubt that animal life was significantly affected by the SO2.



> Also, don't flood basalt volcanoes
> put out iridium?

Yes, but iridium in an aerosol form (which would be required if it supposadly 
innoculated the entire earth in a thin layer) is less commonly produced by 
flood basal eruptions than is the iridium trapped in the lava itself, which is 
significant.

The thousands of tons (or millions of tons?) of Ir found in the Deccan Trap 
basalt is probably still in the Deccan region, not having traveled very far 
from its source (except for weathering and erosion).

If Deccan-Trap-correlative sedimentary units can be found in other places (such 
as in southern India), this might make a neat little research project for a 
graduate student.  See what type of a Deccan iridium "fingerprint" can be found 
in distant correlative sedimentary units.

Studying the isotopic ratios of Ir may prove useful.  There are two common 
stable isotopes of iridium.

<pb>



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