The Grand Canyon a long narrow gorge in arizona is rich in geological history . its record of past plant and animal life also makes it an exciting and invaluable object of study  for biologists. Using samples  from the two hundred and seventeen miles of the canyon's walls, scientists analyze the building materials that from  the earth's surface and study  the natural process wich have affected the canyon over its four-billion-year history.These processes include  the eruption of volcanoes,wich were active as recently as one thousand years ago,and gradual decomposition by erosion, Scientists also study  a great variety of fossils that can be found in the canyon.These imprints of past forms of life are preserved in rock.Tje lower levels of canyon rock contain fossils of seashells and primitive algae,while the upper levels contain  fossils of such  creatures as dinosaurs and other prehistoric land animals .All of these discoveries  provide scientists with informaton both on the  earth's history  in general and on the area around the Grand Canyon in particular