PLATE TECTONICS INTRODUCTION

Chapter 9

EARTH’S STRUCTURE

Earth’s interior consists of three major zones defined by its chemical composition:CrustMantleCore

CRUST Thin, rocky outer layer of Earth

The crust is mainly composed of igneous rock Divided into continental and oceanic

Continental crust is about 5-47 miles thickOceanic crust is about 4 miles thick

Crust and upper most part

of the mantle make up the

lithosphere

MANTLE Solid, rocky shell that extends to a depth

of about 1,800 miles Upper Mantle:

Lithosphere○ Rigid

Asthenosphere○ Soft, flexible

Lower Mantle

CORE Sphere composed of iron-nickel alloy Outer core

Liquid layer is about 1,400 miles thickEarth’s magnetic field is generated from the

flow of metallic iron Inner core

Radius of about 760 milesDue to the extreme pressure, the material is

solid

CONTINENTAL DRIFT HYPOTHESIS A German scientist and meteorologist,

Alfred Wegener, proposed a hypotheses:The continents had once been joined to

form a single supercontinent, Pangaea○ Pangaea meaning all land

CONTINENTAL DRIFT EVIDENCE The Continental Puzzle

Similar coastlines on opposite sides of the oceanContinents fit together, like a puzzle

Matching FossilsFossil organisms found on different landmasses

Rock Types and StructuresSeveral mountain belts end at one coastline and

reappear on a landmass across the ocean○ Appalachian Mountains in US, ending off the coast of

Newfoundland (Figure 4 on page 251)

Ancient ClimatesGlacier evidence, Figure 5 on page 252

MATCHING MOUNTAIN RANGES

GLACIER EVIDENCE

A NEW THEORY EMERGES… Wegener could not provide an explanation of

exactly what made the continents moveData on earthquake activity and Earth’s magnetic field

became available By 1968, these findings

led to a new theory,

plate tectonics

PLATE TECTONICS THEORY

The upper most mantle and crust, behave as a strong, rigid layer known as the lithosphereLithosphere is divided into plates, which move

and continually change shape and size Under the lithosphere, there is a layer of mantle that

is super soft (like melted plastic) that the plates float on top ofThis layer is called the asthenosphere7 major plates (pages 256-257, Figure 8)The grinding movements of the plates

generate earthquakes, create volcanoes and deform masses of rock into mountains

The plates do not just move in one direction3 Types of Movements

○ 1.Convergent: Coming together○ 2. Divergent: Moving apart○ 3. Transform (fault):Sliding past each other

All plates are moving at all timesThere are two types of plates:

○ Continental Plates and Oceanic platesEach plate could be doing all three motions, just on

different sides of the plateThese movements will create the landscapes and

mountain ranges that cover the lands and ocean floors, and other hazards that we come in contact with

Plate Movements

PLATE BOUNDARIES Convergent

Two plates move together Divergent

Two plates move apart Transform (fault)

Two plates slide past each other