CHAPTER 4 Created by Miss McDevitt PLATE TECTONICS CHAPTER 4 Created by Miss McDevitt

FORMATION OF EARTH AGE OF EARTH -4.6 BILLION YEARS BIG BANG THEORY – 15 BILLION YEARS AGO BIG BANG ANIMATION formed from cloud or clouds of dust which was debris from huge explosion 3 theories evolved form how Earth formed Earth was very hot: 1. from colliding particles 2. compression of layers 3. radioactive materials

HOW DO WE KNOW EARTH IS LAYERED? Seismic Waves - speed & path of the 3 types of waves created by earthquakes Rock Samples - scientists can make inferences about the conditions inside Earth

FEATURES OF LAYERS Temperature - surface to 20m is rock which is cool -below 20m the deeper you go the warmer it gets (every 20m = 1° C increase) Pressure -deeper you go the greater the pressure -inner core is 2 million X greater than the atmosphere’s pressure

LAYERS OF EARTH

THE CORE INNER CORE -solid due to high pressure -5000°C -made mostly of iron (Fe) -also composed of Ni (nickel), Si, Al OUTER CORE - molten, liquid -2200°C - Fe & Ni -creates Earth’s magnetic field

MANTLE AS A WHOLE Molten Rock Mg, Si, O, Al, Fe, Ca ASTHENOSPHERE Upper Part of Mantle Semi-solid/semi-liquid rock (tar-like) Convection current occur here This layer flows LITHOSPHERE Crust & upper part of mantle Solid rock AKA “the plates” Floats on the asthenosphere

CRUST Outermost layer Made of solid rock Brittle layer Under oceans  3-6 miles thick , mostly made of basalt Under continents  20-40 miles thick, mostly made of granite

LAYERS COMPARED

HEAT TRANSFER Radiation – heat transfer through empty space Conduction – heat transfer through solids Convection – heat transfer through liquids & gases

CONTINENTAL DRIFT THEORY Introduced in 1912 by German meteorologist Alfred Wegener The Origin of the Continents and Oceans - 1915 Evidence that the continents had moved across Earth’s surface and formed the supercontinent of Pangaea Pangaea eventually broke up over tens of millions of years

WEGENER’S EVIDENCE Landforms Fossils Climate

LANDFORMS Continental Animation

FOSSILS

PANGAEA N.A. Africa S.A. India Australia Antarctica

FAILURE TO LAUNCH Wegener’s Problem Could not provide a mechanism to help prove this movement

SEA-FLOOR SPREADING 1960 – Harry Hess (American geologist) Discovered an undersea mountain range (Mid-Atlantic Ridge) He discovered the ocean floor moved like a conveyor belt He also found that magma erupts from the middle of ridge

WHAT IT LOOKS LIKE! Sea-floor spreading

EVIDENCE Alvin- found magma at bottom of sea floor Alvin – took drilling samples (discovered ages of rocks) Magnetic stripes on the ocean floor Warmer in the center of ridge due to magma erupting

MAGNETIC STRIPES Magnetic reversals

PLATE TECTONICS THEORY Developed by J. Tuzo Wilson Earth’s plates (lithosphere) are in constant motion due to convection currents

PLATE BOUNDARIES Extend deep into lithosphere Faults (breaks in Earth’s crust) form along these boundaries 3 types

DIVERGENT CONVERGENT TRANSFORM

TRANSFORM Plates slip past each other Move in opposite directions of one another Ex: North American - Pacific

DIVERGENT Plates move away from each other Most occur at the Mid-ocean ridge 2 Types: 1. ocean-ocean (ridge forms) 2. continent-continent (rift valley forms)

TYPES OF DIVERGENT BOUNDARIES

CONVERGENT Plates move toward each other Density determines which plate comes out on top 3 types: 1. ocean-ocean (trench forms) 2. continent-continent (folded mtns. form) 3. ocean-continent (volcano forms)

TYPES OF CONVERGENT BOUNDARIES

MAJOR PLATES North American South American Pacific Indian Indo-Australian Antarctic African Eurasian Nazca

MINOR PLATES Somali Phillipine Scotia Cocos Caribbean Juan de Fuca Arabian