Download Plate Tectonics Chapter 5

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 1oC 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