  | 
      | 
      | 
      | 
      | 
      | 
   
   
    | q | 
    Ice cores retrieve climate records extending back thousands of years
    in 
     | 
     | 
   
   
     | 
    small mountain glaciers to as much as hundreds of thousands of years
    in 
     | 
   
   
     | 
    continental sized ice sheets. 
     | 
     | 
   
   
     | 
   
   
    | q | 
    The antarctic ice sheet has layers that extend back over 400,000
    years. 
     | 
     | 
   
   
     | 
   
   
    | q | 
    The Greenland ice sheet has layers that extended back 100,000 years. 
     | 
     |