From the perspective of geologic time, the
period from Earth's beginning more than 4-5 billion years ago to the pres-
present day, however, the surface of the planet is in constant motion, being
reshaped over and over. The constructive and destructive forces at play in
this reshaping have helped create landforms, specific geomorphic features
on Earth's land surface. Mountains and canyons, plains and plateaus, faults
and basins: These are but a few of the varied and spectacular features that
define the landscape of the planet.