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