Andrew,
Good point.  I believe the demise of Earth will come from Global Warming.  
This from the fact all humans need heat to survive...  Whether it is to cook 
food, heat their homes or to drive to work (which produces heat), all humans 
need heat.  The more humans on Earth, the more heat produced, the warmer the 
plant becomes.  ZPG was really popular when I was a teen yet we hear nothing 
of it now.  Hmmmmmm.  I tend, therefore, to agree with you.
Jaime
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