1. what caused the formation of the Grand Canyon?

a. Continental drift

b. Subsidence

c. Physical erosion

d. A tsunami

2. why is the harder for the earth to recover from some natural disaster now?

Physical erosion

Today the water not only sweeps up the dirt that has been cleared and manicured, but the cars and their tanks of gasoline and crankcases of oil, and asphalt and concrete, and the houses and all kinds of manufactured stuff and wires and pipes and household chemicals on and on, to leave a nice debris field of junk and toxic waste behind.

B subsicende by colorado river in millions of years