Re: Impact QUestion - Re: The birds vs. the pterosaurs

[Marilyn Wegweiser <mdwegweiser@bsuvc.bsu.edu>]

Hi Rich,

At 12:43 PM -0700 2/11/01, Richard W Travsky wrote:
> On Mon, 12 Feb 2001, Dann Pigdon wrote:
> >  [...]
> >  Not all the plants would have died. Those living in polar environments
>  > would have been used to going several months with complete darkness.

Antarctica had a unique environment due to the geographic location of 
the continent, and the types of currents developing about it.

>  > Other species elsewhere could also have become dormant. Insects
>
> Where was the equator at the time of the impact

Sorry to do this but it is a wide open door - In the same place that 
it is now, at ZERO degrees latitude. ;^)

Now, if you mean where was north America at the end of the late 
Cretaceous then: go here for a look at the current more or less 
accepted configuration:
http://www.scotese.com/lcretcli.htm

>  and where was the impact
> located in relation to the equator?

I will conclude, that with your questions that you are looking at a 
particular single "impact" event - keep in mind that there have been 
several impacts throughout geological time - just look at the moon; 
the only difference is that on this planet we have erosion and 
weathering. Keep in mind also, that Ir is a "heavy mineral" and is 
prone to concentration, and has other sources. (Devil's Advocate) To 
answer your question with a visual go to 
http://www.scotese.com/K/t.htm and check the "Paleomap" pages and you 
will note that North America was just about almost in the position 
that it is in today, and where the impact crater that everyone 
focuses would have been, with respect to your questions.

>  If the impact occurred in the summer
> of the impact's associated hemisphere, would this not have given an
> advantage to the organisms in the hemisphere that was in winter? (Side
> question: did summer and winter exist as we know them?)

Paleoclimate is indeed something many of us are interested in. A true 
Circumpolar Current did not set up in Antarctica simultaneously with 
the impact. The Deep Freeze took a bit later to occur. It had to wait 
until the continents drifted a bit farther apart. Note that by the 
Miocene (http://www.scotese.com/miocene1.htm) Antarctica was 
"orphaned" by the currents and as such, all was in place for some 
rather cold weather to become the 24/7 norm. Ocean currents have an 
intense effect on continental climate.

>  I say "advantage"
> as these organisms would already have been in a "powered down" mode...

Not necessarily - only, if they did it.

Cheers,
(tell Brent please, if you see him, that I need to talk to him 
tomorrow wrt my Friday afternoon phone call)

Marilyn W.
--
                        =00=  =00=  =00=  =00=
                        Marilyn D. Wegweiser, Ph.D.
                Adjunct Curator of Vertebrate Paleontology
                     Cincinnati Natural History Museum

Assistant Professor of Geology
Department of Geology                   mdwegweiser@bsu.edu
Ball State University                   Office: 765-285-8268;765-285-8270
Muncie, Indiana                         FAX:    765-285-8265