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