Bellringer: Looking at the world Bellringer: Looking at the world map, what do you notice about map, what do you notice about the shape of the continents?the shape of the continents?

-Write a 1 paragraph response about what you notice.-Write a 1 paragraph response about what you notice.

From the time maps of the globe became available, people wondered about the

arrangement of the continents and oceans. Hundreds of years later, valid explanations

were constructed.

Continental Drift and Plate TectonicsContinental Drift and Plate Tectonics

In the early 20th century a meteorologist named Alfred Wegener created the theory of

continental drift, the idea that all of the present-day continents were connected,

side-by-side. He called the supercontinent Pangaea.

Greek for ‘all lands’.

PangaeaPangaea

o Pangaea began to split apart 200 million years ago

o DiagramNorth America

Laurasia GreenlandEurasia

PangaeaAfricaWest G. S.America

GondwanalandAntarctica

East G. AustraliaIndia

Pangaea—A History of the Continents: 2:23

Wegener’s summary was based on a number of careful observations:

Wegener’s EvidenceWegener’s Evidence

-- matching rock, fossil, glacier, and structural relations among different

parts of different continents

Glacial Glacial Evidence Evidence -Large ice masses

carve grooves in the rocks over which flow.

-Such masses tend to

flow outward (generally downhill)

from a central location.

-Glaciation patterns indicate a common ice cap at the South Pole.

Continental Drift: Continental Drift: Rock AgesRock Ages

-Using geochronology, rock dating, rock ages showed strong correlation across the Atlantic.

-Mountain ranges of similar ages across the Atlantic also show a correlation that they used to be part of the same mountain ranges.

o PaleomagnetismPaleomagnetism (magnetism of old rocks) indicate a common pole if the continents were all connected

But how is this possible?!?!?But how is this possible?!?!?

-Wegener never lived to see the general acceptance of continental drift, largely because of the lack of a mechanism.

The lithosphere is divided into a number of large and small tectonic plates and the plates are floating on the mantle.

The plates move at a rate of cm’s per year.

Plate Tectonics Plate Tectonics TheoryTheory

Convection CurrentsConvection Currents

• Hot magma in the Earth moves toward the surface, cools, then sinks again.

• Creates convection currents beneath the plates that cause the plates to move.

Bellringer: Name and explain what process this diagram is depicting. Then, explain how this is connected to what we are studying.

o Sea-floor spreadingo Magnetic reversalo Earthquakeso Mountainso Volcanoeso Subduction

What evidence do we have What evidence do we have to support this idea of plate to support this idea of plate

tectonics?tectonics?

Seafloor SpreadingSeafloor Spreading• As the seafloor spreads apart at a mid-ocean ridge,

magma rises to the surface and solidifies and new crust forms.

• Mid Ocean Ridges – underwater mountain chains that run through the ocean floor

• The older seafloor moves away from the ridge in opposite directions.

• This helped explain how the crust could move—something that the continental drift hypothesis could not do.

o Noo Plates are destroyed as fast as

they are created (2 ways)o Plates may be subducted and

melted or may be pushed upward to form mountains.

So is the Earth So is the Earth getting bigger?getting bigger?

Polar Reversal MagnetismPolar Reversal MagnetismPolar reversal magnetism Polar reversal magnetism

proves that the ocean floor is proves that the ocean floor is moving away from the ridgesmoving away from the ridges

BellringerThe 3 types of plate boundaries are shown in the pictures below. Name each boundary and describe its motion.

Plate Boundaries

Plate Boundaries

1-Divergent Boundaries1-Divergent Boundaries

• Boundary between two plates that are moving apart or rifting

• RIFTING causes SEAFLOOR

SPREADING

Geographic Features of Geographic Features of Divergent BoundariesDivergent Boundaries

• Mid-ocean ridges (sea-floor spreading)

• rift valleys

• volcanoes

Leif the Lucky Bridge Bridge between continents in southwest Iceland across the Alfagja rift valley, the boundary of the Eurasian and North American continental tectonic plates.

Divergent Boundary – Divergent Boundary – Arabian and African PlatesArabian and African Plates

2- Convergent 2- Convergent BoundaryBoundary: plates are moving toward each other and are colliding (3 types)

Type 1Type 1• Oceanic-Continental• Subduction Zone: where the

more dense plate slides under the less dense plate

• VOLCANOES occur at subduction zones

Oceanic-Continental Collision

Type 2Type 2

• Oceanic-oceanic

• The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH

Oceanic-Oceanic CollisionOceanic-Oceanic CollisionIsland arcs are created (a pattern of volcanic islands

created from a subduction zone that is located off the coast)

The Mariana Trench is the deepest part of the world's oceans. (About 36,000 ft)

Type 3Type 3

• A continental plate colliding with another continental plate

• Have Collision Zones:–a place where folded and thrust

faulted mountains form.

• MountainMountain rangesranges are created

Continental-Continental CollisionContinental-Continental Collision

Himalayan MountainsHimalayan Mountains

Mountains 2:46

3- Transform 3- Transform BoundaryBoundary Plates are neither moving toward

nor away from each other, they are moving past one another.

The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created

San Andreas Fault, San Andreas Fault, CaliforniaCalifornia