Plate Tectonics

Earth’s Drifting Continents

• The theory of continental drift • stated by AlfredWegener, a German

meteorologist

• Earth once had a single landmass that broke up into pieces, which have since drifted apart.

• Scientists call this giant landmass, Pangaea, which means all Earth.

Evidence from Climate

• Glacial remnants found in areas of warm climate also provide evidence.

• Wegener thought that these areas nowhere near each other now, were once connected

Evidence from Fossils

• Identical fossils found in both South America and Africa• How did they get there?• supports Wegner’s theory that all land

was connected

• Fossils of the Kannemeyerid, a reptile, have been found in both eastern North America and northern Africa.

Evidence from Fossils

• Fossils of Glossopteris, an extinct plant, found in rocks from South Africa, Australia, India and Antarctica provide support. • seeds too large to have been

carried by the wind and too fragile to have survived the ocean waves.

Antarctica

• The presence of Glossopteris fossils in the frozen wasteland of Antarctica also indicate that the climate must have changed greatly. Antarctica must have changed position.

• An ancient folded mountain chain formed in Africa lines up with matching folded mountains in South America.

• Coal field layers found in Brazil line up with coal field layers in Africa.

Evidence from Fit of Continents

• An ancient folded mountain chain formed in Africa lines up with matching folded mountains in South America.

• Coal field layers found in Brazil line up with coal field layers in Africa.

Evidence from Rock

Evidence from Rock

• Salt deposits normally formed between 35 and 10 degrees North and South of the equator are found as far north as Michigan.

Were there any doubts or questions to Wegener’s theory

of continental drift? Wegner thought that the continents pushed through the ocean floor. Pushing it and tearing it up to create new mountains and landmasses.

He was wrong…how do they move?

The continents are on plates. The plates moved with the ocean floor.

Exit Card Answer the following on the index card and hand to Mrs. Wowkun.

She will give you your homework and you can get started!

Name:

What were the four types of evidence found to support the theory of continental drift? Name the topic, and explain briefly with an example.

Yesterday’s Exit Card

1) Fossils – Kannemeyerid, reptile, found in North America and Africa or Glossopteris, plant fossil, found oceans apart

2) Climate- evidence of glaciers in areas that are warm temperatures today

3) Fit- the fit of South America and Africa 4) Rock- mountain chains line up in Africa and South

America, same age and rock type

Chapter 10, Section 1 Review

1) Fossils of warm weather plants were found on islands in the Artic Ocean and glacial features were found in places like Africa. These supported the idea of continental drift.

2) Rock structures on different continents were similar.

3) Fossils of the same terrestrial organisms were found on widely separated continents.

4) The same rock structure they shared when attached would appear on both halves after the landmass split apart.

Earth’s Spreading Ocean Floor

http://www.youtube.com/watch?v=ryrXAGY1dmE&feature=related

Earth’s Spreading Ocean Floor

• Scientists discovered a large system of underwater mountains that have a deep crack, called a rift valley, running through their center, known as the midocean ridges.

Mid Ocean Ridges

• A great deal of volcanic activity occurs at the midocean ridges.

• Lava erupts from the rift valley.

• The hardened lava forms new ocean floor.

• This process is known as ocean-floor spreading.

Proving continental drift?

• Ocean-floor spreading helps to explain how continents drift.

• As a piece of the ocean floor moves, it takes its continent (if it has one) with it.

Magnetic Stripes

• A permanent record of the Earth’s magnetism remains in the rocks.

• Scientist discovered that the Earth’s magnetic poles reverse themselves from time to time. Studies show that during the past 3.5 million years, the magnetic poles have reversed themselves nine times. The pattern is identical on both sides of the midocean ridge.

Transform Faults• Individual sections of midocean ridges are straight but the

ridges as a whole curve.• This is because the straight sections are offset by thin

cracks known as transform faults.• The youngest rock is near the midocean ridge. • As the floor spreads, older rocks move farther away from

the ridge.

• http://www.youtube.com/watch?v=Tlzg5_hVaPU

• To understand fully how the plates are moving and constantly being recycled we need to know what the Earth looks like under the crust

• Open the PLATE TECTONICS science software

• Complete the EARTH’S INTERIOR section• Click intermediate

• Use the worksheet “LABEL THE EARTH DIAGRAM” to take notes

• Take good notes (NOT every word) you will be quizzed on this section next week

Earth’s Interior

Earth’s Interior

Earth’s Interior• Inner Core: A solid, dense inner core made mostly of

iron with smaller amounts of nickel, oxygen, silicon, and sulfur.

• Outer Core: A liquid layer made mainly of iron. • Mantle: Largest layer. Directly above outer core. Made

mostly of silicon, oxygen, magnesium, and iron. Divided into two layers – upper and lower mantle.

• Asthenosphere: The upper mantle. It consists of weak rock that can flow slowly.

• Lithosphere: Made up of Earth’s crust and a part of the mantle just beneath it.

Lithospheric Plates

• The topmost solid part of the Earth, called the lithosphere, is made of a number of plates. The plates contain a thin layer of crust above a thick layer of relatively cool, rigid mantle rock. Plates usually contain both oceanic and continental crust.

• There are seven major lithospheric plates, each of which is named after its surface features.

Seven Lithospheric Plates

• The Pacific plate covers 1/5 of the Earth’s surface.

• The other major plates are the North American, South American, Eurasian, African, Indo-Australian and Antarctic plates.

• There are also smaller plates such as the Caribbean and Arabian plates.

Plate Motion

• Scientists hypothesis is that plates move because of large convection currents within the Earth

• A convection current is the movement of material caused by differences in temperature.

• Mantle material close to the core is very hot. • Mantle material farther from the core is cooler and less dense. • Rising and sinking of magma occurs in a circular motion.

Types of Plate Boundaries

• There are three types of plate boundaries.

• Divergent

• Convergent

• Transform

Plate Boundaries• When plates move, they can interact in several

ways:

1) They can pull apart from one another (Divergent).

2)They can move toward each other (Convergent).

3)They can slide alongside one another (Transform)

• When plates interact, the result of their movement is seen at the plate boundaries.

Divergent Boundaries

• The first type occurs at midocean ridges.

• the plates move apart, the ridges are called divergent.

• These boundaries are also called constructive boundaries. (why??)

Divergent Plate Boundaries

• There are 2 types of Divergent boundaries When two oceanic plates DIVERGE the result is a fissure under the ocean. The ocean floor is growing.

Divergent Plate BoundariesContinental Rifting

When two continental plates DIVERGE the result is a rift valley on land. The crust of the Earth is growing.

Convergent Boundaries

•Boundaries where plates come together are called convergent. • also called destructive boundaries.

• Convergent boundaries form trenches

•The collision of plates at convergent boundaries causes tremendous friction and pressure. Earthquakes often result. • Ring of Fire follows the major ocean trenches in that area.

http://www.youtube.com/watch?v=cVzBTS2UUuA&list=PL5FA7B0536C11CCFE&index=2&feature=plpp_video

Convergent Plate Boundaries

• When an oceanic plate converges with a less dense continental plate, the denser oceanic plate sinks under the continental plate.

• The area where an oceanic plate subducts, or is pushed down, into the mantle is called a subduction zone.

• Volcanoes form above some subduction zones.Three types of convergent plate boundaries – 1.oceanic to ocean2.ocean to continent3.continent to continent.

1) Ocean to Ocean Plate Collision

• older oceanic plate is subducted under the younger • (Plates grow denser as they cool.)• The plate being subducted melts.

• Molten rock then rises up and breaks through the surface.

• As a result, a string of volcanoes erupts on the ocean floor along the trench.

• Some rise above the ocean’s surface as a string of islands, such as Japan &the Aleutian Islands (know another one?)• VOLCANIC ISLAND ARC

Convergent Plate Boundaries

Ocean to Ocean

• This type of convergent boundary creates a deep-sea trench where one plate bends and sinks beneath the other, creating a volcanic island arc.

2) Oceanic/Continental Plate Collision

• Oceanic plates are more dense than continental plates.

• During ocean-Continent collisions subduction occurs

• The subduction of the oceanic plate pushes up and folds the continental crust on the edge of the continental plate and forms mountain ranges such as the Andes of South America.

• These mountains can have active volcanoes in them

Convergent Plate Boundaries

Ocean to Continent

• This type of convergent boundary creates a deep-sea trench where one plate bends and sinks beneath the other, creating a volcanic mountain chain on the continent.

3) Continent to Continent Plate Collision

• When two continental plates collide, the edges of the continents fold upward to form large mountain ranges, such as the Appalachian Mountains. • when Africa collided with North

America during the formation of Pangaea. • Example: Himalayas.

Convergent Plate Boundaries

Continent to Continent

• This type of convergent boundary creates a large mountain chain between the colliding plates.

• Usually, no subduction occurs when two continental plates collide.

Transform Faults (strike slip boundaries)

• No new plate material is destroyed or made.

• formed by a lateral fault.

• formed by lateral boundaries are called transform faults.• (strike slip boundaries)

•

• two plates grind together and slip past each other horizontally

• Earthquakes often occur along strike-slip boundaries• San Andreas Fault.

Transform Plate Boundaries

• They move in opposite directions or in the same direction at different rates.

Possible Changes in Plates

• Any change in one plate or boundary affects all the other plates and boundaries. There are many changes that can occur in plates and their boundaries. Continental plates may fuse together. A trench may switch direction and begin to subduct a formerly overriding plate. New divergent boundaries may form in the center of continents. Plates may also be completely subducted and disappear.

Earth’s Moving Plates

• The word plate refers to the moving, irregularly shaped slab that fit together like paving stones to form the surface of the Earth.

• The word tectonics refers to the branch of geology that deals with the movements that shape the Earth’s crust.

• The theory of plate tectonics links continental drift and ocean-floor spreading to explain the formation, collisions, movements and destructions of the Earth’s crust.