Plate Tectonics Chapter 5
Earth s Interior Scientists learn about the interior of Earth in 2 ways Direct Method Rock Samples Drilling Caves
Earth s Interior Indirect Method Seismic Waves Speed of waves and paths shows the structure of the planet»show that the earth is made up of several layers
Seismic Waves
The Layers of the earth vary in several ways Temperature Gets warmer as you descend toward the center of the earth Temperature rises 1 o C for every 40 meters descended Pressure Pressure increases as you descend
The Layers of the Earth
The Crust The Crust Outer Layer Includes dry land Includes the ocean floor Includes Water and soil
The Crust Thinner than other layers Thinnest under oceans Called oceanic crust»composed of BASALT Thickest under mountains Called continental crust»composed of Granite
The Mantle 40 Km below surface Hot Solid Rock About 3000 km thick
The Mantle Divided into layers Lithosphere Upper part of mantle Rigid Layer
The Mantle Asthenosphere Below lithosphere Hotter Increasing pressure Softer but still solid
The Mantle Lower Mantle Under Asthenosphere Solid- extends to the core
The Core Made of iron and Nickel Has 2 parts Outer Core Liquid Molten(melted) metal surrounding inner core Inner Core Dense ball Solid metal
The Core Creates a Magnetic Field Due to movement in the core Magnetic poles
Types of Heat Transfer Radiation: transfer of energy through space No direct contact between heat source and object Examples The sun Fire
Types of Heat Transfer Conduction: heat transfer within a material or between materials that are touching Responsible for some of the heat transfer within the Earth Example: metal spoon in a hot pot
Types of Heat Transfer Convection: heat transfer by the movement of currents in a fluid Caused by differences in temperature and densities in a fluid Examples Convection zone in the sun Deep currents in ocean
Convection Currents in the Earth Mantle Heat from the mantle causes convection current Moves the plates of the lithosphere Core Heat in the outer (liquid) core causes a convection current Causes Earth s magnetic field
Continental Drift Alfred Wegner Thought all continents formed Pangaea at one time Pangaea: a single land mass Evidence Shape of the continents Fossils»Glossopteris Climate
Continental Drift Wegener s theory was rejected He could not explain the forces that push and pull the continents
Seafloor Spreading Mid Ocean Ridges Tall mountain ridges hidden under the oceans Curve around the world In a few places the ridge or mountain is above the surface of the ocean Example: Iceland
Mid Ocean Ridges Mapped using Sonar Sonar is a device that bounces sound waves off underwater objects and then records the echoes of the sound waves
Sea Floor Spreading Sea floor spreads apart along both sides of the mid ocean ridge Adds New Crust Ocean floor like a conveyor belt Carries continents
Evidence of Sea Floor Spreading Molten material Submarine Alvin finds pillow shaped rocks These rocks only form when molten material cools quickly
Evidence of Sea Floor Spreading Magnetic strips The earth s magnetic poles have reversed many times Evidence in the rocks on the ocean floor
Magnetic Stripes
Evidence of Sea Floor Spreading Drilling Samples The samples far from the ridge are older The youngest rocks near the center of the ridge
Subduction at Trenches Process by which ocean floor sinks under the trench and back into the mantle Crust near ridge moves away from ridge Like a giant conveyor belt
Subduction at the Trenches The ocean floor Pacific Ocean is shrinking Lots of deep trenches Trench swallows more of the floor faster than its made Atlantic Ocean expanding Oceanic crust attached to the continental crust Continents move
Theory of Plate Tectonics J. Tuzo Wilson Scientist who discovered the plates Plates: a section of the lithosphere that slowly moves over the Asthenosphere carrying pieces of the continental and oceanic crust
Theory of Plate Tectonics Combined continental drift and sea floor spreading into a scientific theory Scientific Theory: well tested concept that explains a wide range of observations Ideas that are supported by data.
How Plates Move Theory of Plate Tectonics Earth s lithosphere is in constant, slow motion driven by the convection currents in the mantle.
3 ways of moving Collide (convergent) Pull apart (divergent) Grind past each other (transform) Each changes the earth s surface
Plate Boundaries Extend deep into the lithosphere Faults: breaks in Earth s crust where rocks have slipped past each other Move Slowly
3 types of Boundaries Divergent (Move apart) Convergent (Collide) Transform (Move past)
Divergent Boundaries Plates move away from each other Most occur along the mid ocean ridge Where sea floor spreading occurs Can occur on land Forms a Rift Valley A deep valley
Convergent Boundaries Two plates that come together or collide Density of the plates determine which plate is on top Oceanic crust vs. continental crust Subduction. Continental crust vs. continental crust Mountains are squeezed from the crust
Transform Boundaries 2 plates slip past each other Earthquakes are common Crust is neither destroyed or created