Plate Tectonics Introduction Chapter 9 Plate Tectonics Introduction

Earth’s Structure Earth’s interior consists of three major zones defined by its chemical composition: Crust Mantle Core

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 thick Oceanic 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 Inner core Liquid layer is about 1,400 miles thick Earth’s magnetic field is generated from the flow of metallic iron Inner core Radius of about 760 miles Due 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 ocean Continents fit together, like a puzzle Matching Fossils Fossil organisms found on different landmasses Rock Types and Structures Several 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 Climates Glacier 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 move Data 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 lithosphere Lithosphere 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 of This layer is called the asthenosphere 7 major plates (pages 256-257, Figure 8) The grinding movements of the plates generate earthquakes, create volcanoes and deform masses of rock into mountains

Plate Boundaries Convergent Divergent Transform (fault) Two plates move together Divergent Two plates move apart Transform (fault) Two plates slide past each other