Re: Hell Creek (long)

["Steve Brusatte" <dinoland@lycos.com>]

On Sat, 01 Jun 2002 23:21:42  
 Tommy Tyrberg wrote:
>I don't think that any credible decrease in atmospheric oxygen would have a
>very significant effect on animals. Extant animals certainly have a fairly
>high tolerance in this respect... Birds are _incredibly_ tolerant. Many species
>regularly migrate at altitudes up to 25-30,000 feet which means that they
>can not only survive but also sustain intense and prolonged physical
>activity at oxygen pressures that will kill most mammals within a few
>minutes. 
>This is usually explained as being due to their "stream through" breathing
>system in contrast to the "dead-end" mammalian breathing apparatus. 

Most definitely.  First, we have to remember the most of the oxygen evidence 
comes from amber bubbles, which was mentioned onlist a few days ago.  I don't 
know how reliable these estimates are.  And, even if they are reliable, an 
oxygen decrease isn't a very convincing extinction mechanism when we are 
talking about dinosaurs, some of which likely had avian-style respiratory 
systems, and many bird groups.  Plus, if these changes were gradual, evolution 
would have likely "created" survival strategies in some of the other groups 
(such as some mammals and reptiles) that may have been more adversely affected.

>Another aspect that I think hasn't been mentioned in this thread is that
>the Chixculub bolide impacted on partly dolomitic rock. This means that
>large amounts of sulphur were injected into the stratosphere. This may have
>had a very significant effect on climate. Microscopic sulfuric acid
>droplets in the stratosphere are the most important component in the "dust
>veil" from volcanic eruptions and since they are so small it takes two or
>three years before they settle out. Unfortunately there is no consensus on
>how much dolomite there really was in the Chixculub target rock. 

Yes, good point.  Everything I've read has said that the bolide likely impacted 
a sulfur-rich carbonate platform/shelf.  Sulfur injected into the atmosphere 
will not only create dust veils, but will also form sulfur dioxides, which 
eventually and easily combine with water to form sulfuric acid.  This may 
explain (as Paul briefly mentions in DA) why the Chixculub impact was 
especially deadly, while other impacts (such as the one that created Chesapeake 
Bay) were not. These "other" impacts, which included one possible one at the TJ 
boundary and others in the Jurassic, Cretaceous, and Tertiary, might have 
either hit in the ocean or in other sulfur-poor areas.

Steve

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