Visualizing Environmental Science

298 CHAPTER 12 Mineral and Soil Resources

0

0 1000 2000 3000 kilometers

1000 2000 3000 miles

60 °S

30 °S

0 °

30 °N

60 °N

60 °S

30 °S

0 °

30 °N

60 °N

Nazca

Plate

African

Plate

Eurasian Plate

Indian–Australian Plate

Antarctic Plate

Pacific

Plate

Juan de

Fuca

Plate

North American Plate

South

American

Plate

Caribbean

Plate

Cocos

Plate

San

Andreas

Fault M

id-At

lan

tic

(^) R
gid
e
E
as
Pt
ac
ific
Divergent boundary
Convergent boundary
Transform boundary
Asthenosphere
Lithosphere
Crust
Upper
mantle
Viscous
nickel
Lower mantle
Solid oxides of iron,
magnesium, silicon
Outer core
Liquid iron
Inner core
Solid iron, nickel
a. The Main Layers of Planet Earth.
b. Plates and Plate
Boundary Locations.
There are seven major
independent plates that
move horizontally across
Earth’s surface. Arrows
show the directions
of plate movements.
The three types of
plate boundaries are
explained in Figure 12.2.

1. Define plate tectonics and explain its
   relationship to earthquakes and volcanic
   eruptions.


2. Diagram a simplified version of the rock cycle.

Plate Tectonics and the Rock Cycle

LEARNING OBJECTIVES

eology is an essential part of environmental

science. To better understand the environ-

mental effects of humans on mineral and soil

resources, you must first know something

about the geologic properties of Earth’s outer layers.

Earth’s outermost rigid rock layer, the lithosphere,

consists of Earth’s crust—the outermost layer—and the

uppermost part of the mantle. It is composed of seven

large plates, plus a few smaller ones, that float on the

asthenosphere, the region of the mantle where rocks be-

come hot and soft (Figure 12.1). Continents and

landmasses are situated on some

of these plates. As the plates move

across Earth’s surface, the con-

tinents change their relative posi-

tions. Plate tectonics, the study

of the movement of these plates,

explains how most features on Earth’s surface originate.

An area where two plates meet—a plate boundary—

is a site of intense geologic activity (Figure 12.2). Three

types of plate boundaries—divergent, convergent, and

transform—exist; all three types occur both in the ocean

and on land. Two plates move apart at a divergent plate

boundary. When two plates move apart, a ridge of molten

rock from the mantle wells up between them; the ridge

continually expands as the plates move farther apart. The

Atlantic Ocean is growing as a result of the buildup of

G

Earth’s layers and surface

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Which plate do

you live on? Are

you near a plate

boundary?

GLOBAL

LOCAL

plate tectonics

The study of the

processes by which

the lithospheric

plates move over the

asthenosphere.