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Chapter 4Chapter 4
The Restless The Restless EarthEarth
The Composition of the The Composition of the EarthEarth
The Crust – outermost layer of the Earth– 5 to 100 km thick– thinnest layer
The Mantle - layer of the Earth between the crust and
the core - much thicker than the crust -contains most of the Earth’s mass
The Composition of the EarthThe Composition of the Earth
The Core - layer of the Earth that extends from below the mantle to the center
of the Earth - made mostly of iron
The Physical Structure of the EarthThe Physical Structure of the Earth
Five Physical Layers
- lithosphere: crust & upper rigid mantle
- asthenosphere: plastic layer of mantle on which
the tectonic plates move
- mesosphere: strong lower part of the mantle (below asthenosphere to the outer core)
The Physical Structure of the EarthThe Physical Structure of the Earth
- outer core: liquid part of the core, below the mantle and
surrounds the inner core
- inner core: solid dense center of our planet
Tectonic PlatesTectonic Plates
lithosphere = a jigsaw puzzle tectonic plates = the pieces
•consist of both oceanic crust and continental crust
•They “float” on the asthenosphere
Mapping the Earth’s InteriorMapping the Earth’s Interior
seismic waves = vibrations produced by an earthquake
-travel at different speeds depending on the density & composition of material
they pass through
seismographs: measure the times at which different seismic waves
arrive and record the differences in their speeds
* calculate the density and thickness of Earth’s layers
Wegener’s Continental Drift Wegener’s Continental Drift HypothesisHypothesis
Continental drift: the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations.
Evidence• fossils of plant & animal species • similar rocks• same ancient climateALL found on continents that are far apart
PangaeaPangaea
* a single huge continent* existed about 245 million years ago
* split into two large continents— Laurasia and Gondwana about 180 million years ago.
* ~65 million years ago split into smaller pieces
Sea-Floor SpreadingSea-Floor SpreadingMid-ocean ridges: places where sea-floor
spreading takes place * magma rises toward the surface and solidifies forming new oceanic
lithosphere
Evidence for Sea-Floor Spreading
Magnetic Reversals: when Earth’s magnetic poles change places* recorded over time in oceanic crust
Mid Ocean RidgesMid Ocean Ridges
mid-oceanic ridge system the longest mountain range in the world
40,400 miles long
like the seams of a baseball
Andes MountainsAndes Mountains
• Run along the coast of South America
• Longest exposed mountain range
• 4,300 mi long
Mid-Atlantic Ridge splitting Iceland and separating Mid-Atlantic Ridge splitting Iceland and separating
the North American and Eurasian Plates.the North American and Eurasian Plates.
East African RiftEast African Rift
Hot spring in central rift valley, near Bogoria
Deepest Part of the OceanDeepest Part of the Ocean
Three Tectonic Plate Three Tectonic Plate BoundariesBoundaries
• Convergent Boundaries : when two tectonic plates collideA. continental-continental : pushes
continental crust upward (mountain ranges)
Subduction Zones (crust is recycled)
B. continental-oceanic: denser oceanic crust gets pushed downinto the asthenosphere
C.oceanic-oceanic: one of the oceanic plates is subducted
• Divergent Boundaries : when two
tectonic plates separate
*mid-ocean ridges (new crust formed)
• Transform Boundaries : when two
tectonic plates slide past each other horizontally
*most found on the ocean floor
Mid-Atlantic Ridge splitting Iceland and separating Mid-Atlantic Ridge splitting Iceland and separating
the North American and Eurasian Plates.the North American and Eurasian Plates.
San Andres FaultSan Andres Fault• The San Andreas fault zone
slices through two thirds of the length of California. Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr. Land on the west side of the fault zone (on the Pacific Plate) is moving in a northwesterly direction relative to the land on the east side of the fault zone (on the North American Plate).
Possible Causes of Tectonic Possible Causes of Tectonic Plate MotionPlate Motion
changes in density within the asthenosphere caused by thermal energy from deep
within the Earth
1. Ridge-push: due to gravity thelithosphere is pulled under
2. Slab- Pull: denser oceanic crust sinks and pulls the rest of the plate with it
3. Convection: hot rock rises, then cooler rock near the surface sinks = cycle
Convection CurrentsConvection Currents
Convection currents in the mantle carry the plates of the lithosphere like a conveyor belt.
• Because ocean floor is continuously created at mid-ocean spreading centers, it is far younger than most continental rock.
• oldest continental crust ~ 3.8 billion years old
• oldest oceanic crust ~ 150 million years old
• Spreading rate of the Atlantic Ocean: ~ 25 mm/yr
Tracking Tectonic Plate Tracking Tectonic Plate MotionMotion
Tectonic plate movements •slow and gradual•can’t see or feel them moving•measured in centimeters per year (cm/yr)
(GPS) global positioning system : a system of satellites used to measure the rate of tectonic plate movement
Convergent Boundaries
Divergent Boundaries Transform
Boundaries
folded mountains
tsunami
major earthquakes
trenches
most volcanic eruptions
fault block mountains
mid-ocean ridges
new sea floor
rifts
weak earthquakes
volcanic eruptions
moderate earthquakes
• Compare the mountains in the photographs. Write a description of each mountain, and suggest how it might have formed. Do you know where these various types of mountains are found in the world? Have you ever visited any of them? Would it ever be dangerous to study them?
• Record your responses in your science journal.
transform boundaries, tectonic plates, converge, divergent transform boundaries, tectonic plates, converge, divergent boundaries, divergeboundaries, diverge
ObjectivesObjectives
• Describe two types of stress that deform rocks.
• Describe three major types of folds.
• Explain the differences between the three major types of faults.
• Identify the most common types of mountains.
• Explain the difference between uplift and subsidence.
DeformationDeformation
Deformation : the process by which the shape of a rock changes because of stress
types of stress
Compression : occurs when an object is squeezed = when two tectonic plates
collide
Tension: occurs when forces act to stretch an object http://scign.jpl.nasa.gov/learn/plate5.htm
FoldingFolding
bending of rock layers because of stress in the Earth’s crust
different types can be large or small
Monocline foldMonocline fold
simplest type of fold Complex FoldComplex Fold
Syncline foldSyncline fold
Anticline fold
result of compressional
stress
Synclinal folds in bedrock, near Synclinal folds in bedrock, near
Saint-Godard-de-Lejeune, CanadaSaint-Godard-de-Lejeune, Canada
FaultingFaulting
• a break in a rock where one rock slides relative to another
• Normal Faults
• Reverse Faults
• Strike-Slip Faults
http://www.physicalgeography.net/fundamentals/10l.html
Animations of FaultsAnimations of Faults
Plate Tectonics and Mountain Plate Tectonics and Mountain BuildingBuilding
Folded Mountains - form when rock layers are squeezed together and pushed upward
Fault-Block Mountains - form when tension causes large blocks of the Earth’s crust to drop down relative to other blocks
Volcanic Mountains – forms when rock is melted in a subduction zone = magma, which rises to the Earth’s surface and erupts
Other Types of MountainsOther Types of Mountains
• Dome Mountains -formed when melted rock pushes its way up under earth
Black Hills, South Dakota & Adirondack Mountains, (NY)
• Residual Mountains are mountains that are really plateaus that have worn down from erosion
Folded vs. Fault-Block MountainsFolded vs. Fault-Block Mountains
Great Rift Valley of AfricaGreat Rift Valley of Africa
Tibetan Plateau
Folded mountainsFolded mountainsMost common type on land
• Appalachian Mountains (eastern North America)- old
• Urals (Russia)- old (200 my)
• Alps mountains (southern-central Europe)
• Himalayan mountains (southwest Asia)- young
Rockies mountains (western N.A.)- young (10-25 my)
Form along faults•Teton Range (Wyoming) •Sierra Nevada mountains = largest in the
US
Fault- Block mountains
Volcanic MountainsVolcanic Mountains
• Andes mountains (western coast of South
America)
• Cascade Range (runs south from British Columbia, Canada, through the U.S. states of Washington and Oregon before it becomes the Sierra Nevada mountain range in northeastern California)
Uplift and SubsidenceUplift and Subsidence
• Uplift: when rocks rise when a weight is removed from the crust
• Subsidence: when rocks sink because
as they cool they become denser
orwhen the lithosphere becomes stretched in rift
zones