Download Chapter 5 Notes: Plate Tectonics Earth’s Interior Direct

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