Geography Reference
In-Depth Information
Chapter 6
Taking Shape: The Land
We Live On
In This Chapter
Examining the inside of Earth
Moving continents
Theorizing about plate tectonics
Giving rise to mountains
Shaking and baking with earthquakes and volcanoes
Considering terms: natural hazards or natural processes?
E arth originated about 4.7 billion years ago as a molten fireball and has been slowly cooling ever
since. As a result, and after so many years, the outermost portion has hardened into a layer of rock
called the
lithosphere
(from the Greek
lithos,
meaning stone). Most of this layer is so hot that it would
literally fry your feet, along with the rest of you.
Fortunately, however, the outermost portion of the lithosphere is relatively cool. This sub-layer, called
the
crust
, is no more than between 5 and 40 miles deep, so it accounts for a very small portion of planet
Earth. But the crust has a degree of importance that is out of proportion to its volume because you live
on it. The crust is your home.
The crust is also home to every kind of landform you have ever seen or will see — mountains, valleys,
plateaus, plains, and so on. These features and more give character to different parts of Earth and are
among the first things that come to many peoples' minds when they think about geography. And in-
deed
geomorphology
, the study of the nature and origins of landforms, is an important sub-field of
geography.
Landforms don't just happen, however. Instead, they are products of a global war of sorts is engulfing
your “crusty home.” The combatants are two powerful opposing sets of forces that shape and reshape
Earth's surface. On the one hand, and the subjects of this chapter,
tectonic
forces (from the Greek
tek-
