Basically, just your basic rice krispie squares recipe with food coloring added.
 1/4 cup margarine 
 40 regular marshmallows 
 1/2 tsp. vanilla 
 6 cups rice krispies 
 green and blue food coloring 
 
 Melt margarine and marshmallows over medium heat in a large pot, stir in vanilla and rice rispies.   
  
 Divide into two bowls 
  
 Add green food coloring to one bowl and blue food coloring to the second. 
  
 Stir 
  
 Allow the children to take a scoop from the blue bowl and a scoop from the green bowl and mash them together in a ball (the earth). 
  
 Set the balls aside until completely cool.