PROBLEM 1. We Learn about Earth's History from Rocks 



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Fig. 479 The Grand Canyofi of the Colorado. Ages ago these strata of sedimentary 

 rock were laid doiim, then raised, forniiiig a plateau. Then the Colorado River grad- 

 ually cut a channel through the rock. Thus fossils buried in very early rocks became 

 exposed, (aeronautical chamber of commerce of America) 



Shale 



Gray 



sandstone 



Red I 



sandstone ;vi; 



Metamorphic 

 rock 







Fig. 480 Ages ago a mountain was pushed up at A (dotted lines) mid later worn down 

 to B. How do geologists know this? In tinie ntore rocks woidd wear away at B imtil 

 the land became level. Explain how fossils can be found near or at the surface, al- 

 though they are in rocks that are very old and that were at one time buried deep 

 below younger rock layers. (American museum of natural history) 



