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The Mammoth Extinctions

 
 
rosborne979
 
  1  
Reply Sun 29 Oct, 2006 10:08 pm
coluber2001 wrote:
It's notable that the only surviving large herbivores, with the exception of the peccary, which is omnivorous, are all ruminants--animals with multiple stomachs for digesting grass forage. Mammoths, mastodonts, ground sloths, horses, and camels were non-ruminants. Camels were primative ruminants with less efficient stomachs. Horses were grazers but with single stomachs and less capable of digesting the worst forage. Deer, elk, caribou, bison, pronghorns all survived and are ruminants.


Nice post Coluber.
Thanks.
0 Replies
 
coluber2001
 
  1  
Reply Tue 31 Oct, 2006 11:46 am
The Milankovitch curve involves three cycles: the eccentric orbit of the Earth around the Sun with a cycle of about 100,000 years; the precession of the equinoxes with a cycle of about 22,000 years; and the axis tilt variation with a cycle of about 40,000 years. I thought the precession and the tilt were one and the same, but there are apparently two different processes here. I think the high and low part of the curves approximately match up to the glaciations, but I'm not sure.

Ice cores taken from the floor of the ocean and based on the ratio of oxygen 18 to oxygen 16--the ratio increases during colder periods--show five glaciations during the last 450,000 years or an average of one per 90,000 years and the cores also show that were probably 30+ glaciations during the past 3,000,000 years or so. Three millions years represents the approximate beginning of the ice age, which we are still in. One of the strongest arguments for the ice age is the movement of the continents up and around the Artic Circle. Three million years ago was approximately the time that the ice caps and sheets began forming.

I know there is confusion about the term "ice Age," but I prefer the term "glaciation" when referring to the growth and retreating of the glaciers that occurred so often during the last 3,000,000 years.

I don't know if this information helps or not, and I forget what the original argument was; however, I don't feel that name calling and the exchange of negative strokes helps, nor is it consistent with the nature of this website. We've all ready had one website,i.e., Abuzz (RIP) succumb due to the excesses of its members.

I think this is an excellent thread, and I wish we had more participants.
0 Replies
 
timberlandko
 
  1  
Reply Tue 31 Oct, 2006 12:51 pm
coluber2001 wrote:
I think this is an excellent thread, and I wish we had more participants.

I agree, coluber, and I wanna say you've offered some valuable posts here. I think perhaps sometimes members see a few typically outrageous wingnut/fringie comments on the first few pages they come to on a thread such as this and decide all is best if they simply pass it by - avoiding irritation.
0 Replies
 
coluber2001
 
  1  
Reply Fri 3 Nov, 2006 12:56 pm
Thanks, Timberlandko. I'm still not sure about the Milankovitch curve. Perhaps, you can help me there. I know it represents the fluctuating insolution intensity, and that the Earth's eccentric orbit around the Sun is one variable, but the tilt of the Earth is what confuses me. I have a geography book that claims that the tilt has a cycle of 40,000 years, which is at odd with the precession, which is 26,000 years. Some else, I read that the curves synchronize every 40,000 years because of the precession and the eccentric orbit. Another source claims that there is an extra variation in the tilt of 40,000 years on top of the precession. It's all very confusing.

The subject of the Pleistocene extinctions is of great interest to me, and I think that the old and widely accepted theory of overhunting of the prey animals just doesn't seem viable to me. What do you think?
0 Replies
 
coluber2001
 
  1  
Reply Fri 3 Nov, 2006 12:57 pm
Thanks, Timberlandko. I'm still not sure about the Milankovitch curve. Perhaps, you can help me there. I know it represents the fluctuating insolution intensity, and that the Earth's eccentric orbit around the Sun is one variable, but the tilt of the Earth is what confuses me. I have a geography book that claims that the tilt has a cycle of 40,000 years, which is at odd with the precession, which is 26,000 years. Somewhere else, I read that the curves synchronize every 40,000 years because of the precession and the eccentric orbit. Another source claims that there is an extra variation in the tilt of 40,000 years on top of the precession. It's all very confusing.

The subject of the Pleistocene extinctions is of great interest to me, and I think that the old and widely accepted theory of overhunting of the prey animals just doesn't seem viable to me. What do you think?
0 Replies
 
 

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