Questions...Questions...• What is the theory of plate tectonics?• What is the lithosphere?• What is the asthenosphere?• What is the connection between the

two?• What are the two types of plates?

The Earth Has 3 Major LayersThe Earth Has 3 Major Layers

CoreInnerOuter

MantleCrust (Mantle)

AsthenosphereLithosphere

Core Link click here for book

LayersLayers

The CrustThe Crust• The temperatures of the crust is 1600 degrees

Fahrenheit (870 degrees Celsius) in the deepest parts of the crust.

• Composed mostly of oxygen, silicon, and aluminum

• The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material.

What is the What is the LithosphereLithosphere??• The crust and part of the upper

mantle = lithosphere–100 km thick –Less dense than the material below

it so it “floats”–Continental Crust – granite–Oceanic Crust - Basalt

• The oceanic crust consists of a volcanic lava rock called basalt. Basaltic rocks of the ocean plates are much denser and heavier than the granite rock of the continental plates.

• Because of this the continents ride on the denser oceanic plates.

• The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.

• The layer below the rigid lithosphere is a zone of asphalt-like consistency called the Asthenosphere.

• The asthenosphere is the part of the mantle that flows and moves the plates of the Earth.

2 Types of Plates2 Types of Plates• Ocean plates - plates below

the oceans• Continental plates - plates

below the continents

What is Plate Tectonics?What is Plate Tectonics?• The theory that the Earth’s lithosphere is

divided into plates that move on top of the asthenosphere.

• The Earth’s crust and upper mantle are broken into sections called plates

• Plates move around on top of the mantle like rafts

• Plates move along smoothly but sometimes they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this occurs and Earthquake is the result!

Plate TectonicsPlate TectonicsThe Earth is divided into layers due to The Earth is divided into layers due to differences in density. These differences differences in density. These differences are caused by differences in composition, are caused by differences in composition, temperature, and pressure.temperature, and pressure.

Plate TectonicsPlate Tectonics•Theory of Theory of Continental Continental DriftDrift – continents drift – continents drift apart from one another apart from one another and have done so for and have done so for years.years.

The Theory of Continental The Theory of Continental DriftDrift

Continental Drift TheoryContinental Drift Theory

• Proposed by Alfred Wegener in 1912• 250 million years ago, all of the continents

were combined into one super-continent called “Pangea”

• The continents gradually drifted apart to where they are today

PangaeaPangaea• Pangaea was a

time when all land masses on Earth were once together as “all earth”

• Panthalassa was the sea that surrounded all the land – “all sea”

• Pangaea Link

About 180 Million Years AgoAbout 180 Million Years Ago

• Laurasia was the northern part of Pangea composed of N. America and Eurasia

• Gondwana was the southern part of Pangea composed of the remaining continents.

135 Million Years Ago135 Million Years Ago– About 135 million years

ago Laurasia was still moving, and as it moved it broke up into the continents of North America, Europe and Asia (Eurasian plate).

– Gondwanaland also continued to spread apart and it broke up into the continents of Africa, Antarctica, Australia, South America, and the subcontinent of India.

– Arabia started to separate from Africa as the Red Sea opened up.

– The red arrows indicate the direction of the continental movements.

Evidence of Continental DriftEvidence of Continental Drift• Shapes of continents fit like a puzzle• Matching fossils found on different continents • Matching rock formations in Africa and S. America• Glacier patterns

The Same Plant and animal Fossils The Same Plant and animal Fossils found on different coastlines.found on different coastlines.

Same rock patterns found in South Same rock patterns found in South America, India, Africa, Antarctica America, India, Africa, Antarctica

and Australia and Australia

Ancient ClimatesAncient Climates

• Tropical plant remains (coal deposits) found in Antarctica

• Glaciation in Africa, South America, India, and Australia during the same time

Supporting EvidenceSupporting Evidence

• Many years later (1950’s-1960’s) new evidence provided better support like:

1. Earthquake belts2. Locations of volcanoes3. Magnetic reversal showed in igneous

rocks on the ocean floor, Mid-Ocean Ridge

Mid-Ocean RidgeMid-Ocean Ridge

• Seafloor Spreading click here for link and then show Magnetic Reversal after seafloor spreading.

• Iceland straddles the Mid-Atlantic Ridge, and offers a natural laboratory for studying on land the processes that occur along the submerged parts of the Mid-Atlantic Ridge.

Splitting along the N. American and Eurasian Plates as N. America moves westward relative to Eurasia.

Lava fountains (10 m high) spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano. (Photograph by Gudmundur E.

Sigvaldason, Nordic Volcanological Institute, Reykjavik, Iceland.)

Aerial view of the area around Thingvellir, Iceland, showing a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Right of the fissure, the North American Plate is pulling westward away from

the Eurasian Plate (left of the fissure). Large building (near top) marks the site of Lögberg, Iceland's first parliament, founded in the year A.D. 930. (Photograph by Oddur Sigurdsson, National Energy Authority, Iceland.)

More Interesting Stuff!More Interesting Stuff!

• Developing the theory [This Dynamic Earth, USGS]

• Also read magnetic striping and polar reversal, and seafloor spreading.

Convection Currents – the reason Convection Currents – the reason why plates move!why plates move!

• Causes of Tectonic Movement click here for interactive link.

Types of Plate Boundaries: Convergent, Divergent, Transform click here for interactive book.

• Diverging Plate Boundary is where the seafloor spreads.

• Two plates moving in opposite directions

Diverging Plates

Divergent BoundariesDivergent Boundaries• Boundary between two plates

that are moving apart or rifting

• RIFTING causes Seafloor

Spreading, Fissure Volcanoes, Rift Valleys

Diverging BoundaryDiverging Boundarycontinent / continentcontinent / continent

• Rifting happens as they pull apart• Rift valleys and seas form• Great African Rift, Red Sea, Baja California

Convergent BoundariesConvergent Boundaries• Boundaries between two plates

that are colliding

• There are 3 types–Ocean/Ocean–Continent/Continent–Continent/Ocean

Converging Boundary - ocean/oceanConverging Boundary - ocean/ocean• Subduction – more dense plate slides under

the less dense plates• Forms trenches and volcanic island arcs• Aleutian Islands, Mariana Islands, Mariana

Trench (deepest)

Where does the Krakin Live?Where does the Krakin Live?

• Most likely in the Trenches!

• These are the deepest parts of the ocean floor and are created by subduction!

http://blindkat.hegewisch.net/pirates/Nautical_Myths.html#djl

Converging- continent/oceanConverging- continent/ocean

• Subduction • Forms trenches and

volcanic mtn. ranges• Peru-Chile Trench

(longest), Andes Mtns.

Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is pushing into and being subducted under the continental part of the South American Plate. The South American Plate is being lifted up, creating the towering

Andes mountains. Strong, destructive earthquakes and the rapid uplift of mountain ranges are common in this region. The Nazca Plate is sinking smoothly and continuously into the trench, the deepest part of the subducting plate breaks

into smaller pieces that become locked in place for long periods of time before suddenly moving to generate large earthquakes. Such earthquakes are often

accompanied by uplift of the land by as much as a few meters.

Peru-Chile TrenchNazca Plate South

American Plate

The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form towering peaks of the Andes, as seen here in the Pachapaqui mining area in Peru. (Photograph by George Ericksen, USGS.)

On June 9, 1994, a magnitude-8.3 earthquake struck about 320 km northeast of La Paz, Bolivia, at a depth of 636 km. This earthquake, within the

subduction zone between the Nazca Plate and the South American Plate, was one of deepest and

largest subduction earthquakes recorded in South America. Fortunately, even though this powerful

earthquake was felt as far away as Minnesota and Toronto, Canada, it caused no major damage

because of its great depth

Holy Cow !!!

Converging- continent/continentConverging- continent/continent• Collision zones where

folding and thrust fault mountains form

• Himalayan Mtn (tallest), Appalachian Mtns (oldest)

                                       The collision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau.

Convergence of Continent to Continent

Cross sections showing the meeting of these two plates before and after their collision. The reference points (small squares) show the amount of uplift of an imaginary point

in the Earth's crust during this mountain-building process.

Before and After

Wild Beast of the Himalayas

Transform BoundariesTransform Boundaries

• Boundary between two plates that are sliding past each other

• EARTHQUAKES along faults• Most are found under the

ocean floor.

Transform BoundaryTransform Boundary• Zones between

two plates sliding horizontally past one another.

    The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones (transform faults) that scar the ocean floor and offset ridges.

The San Andreas is one of the few transform faults

exposed on land. This fault moves approx. 5 cm/yr.

Transform BoundaryTransform Boundary

San Andreas Fault, CaliforniaSan Andreas Fault, California• Pacific plate moving NW with respect to the

North American plate

The San Andreas fault zone, which is about 1,300 km long and in places tens of kilometers wide, 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).

Good-bye California

Questions...Questions...• What are the three types of

boundaries?• What direction do plates move at

each boundary?• Which boundaries have a

subduction zone…what occurs at a subduction zone?

Questions...Questions...

• What causes plates to move?• How is a convection current

formed?