Plate Tectonics

What is Plate Tectonics?

Theory that earth’s crust is broken into
plates that float on the upper part of the
mantle.

What causes

plate tectonics?

Convection Currents in the mantle

Convection cells in the mantle move the plates.

Hot in the center, less dense magma rises up due to heat.
When the magma reaches the surface, it cools and sinks back down

creating a circular pattern of movement.
Hot – goes UP

Cool– goes DOWN

Continental drift – theory that

the continents were at one or
more times a single landmass
that broke apart and
eventually moved into the
positions they are in today.

Quick Review

• Plate Tectonics: The Earth’s Crust is

Broken into plates that Float on the
mantle

• Continental Drift: The earth’s

Continents were once one piece that
have floated away.

Alfred Wegener – Scientist who
came up with the Theory of
Continental Drift.

Pangaea

The name of the First single landmass

created by Alfred Wegener.

Multiple Choice

What was Pangaea?

• where all the continents were all together

• a new continent

• Evidence for Continental Drift

1. Earth’s continents look like puzzle pieces.

2. Fossils (remember Mesosaurus?)




3. Mountain ranges on different match

4. Rocks – of one continent match those with another.

Divergent Boundaries

● Plates moving apart.

Seafloor Spreading

(oceanic-oceanic)

● The process by which new oceanic crust is

created.

● Two oceanic plates move apart and

magma comes up

● As rising magma cools, it forms new oceanic

crust. (Example: Mid-Atlantic Ridge)

Harry Hess

He proposed the seafloor spreading theory in 1960,
which states that molten material from the Earth's
mantle rises along the mid-ocean ridge system,
cools, and is pushed away from the ridge, creating
a younger ocean floor.

Multiple Select

How do we know that the continents drifted apart? Choose 3

• fossils

• oceans

• rocks

• mountains

Mid-Ocean Ridges

(oceanic-oceanic)

● A mountain under the ocean

● A mid-ocean ridge forms where

oceanic plates continue to
separate.

Convergent Boundaries

● Plates come together

Faults

Large cracks in the earth's crust.

● Types of Faults

– Normal

– Reverse (Thrust)

– Strike-Slip

• There are two (2) kinds of crust:

• Oceanic Crust (ocean)
• Continental Crust (land)

Open Ended

What is the difference between oceanic and continental crust?

• Mid-Ocean ridge: ocean-floor feature

resembling a mountain. (New Sea Floor)

• Rift valley: flat area between two ridges

that is formed by spreading plates.

Seafloor spreading: process that forms new seafloor.
(happens at Mid ocean Ridge)

New Seafloor is close to the Mid-Ocean Ridge…older
floor is Farther away.

Subduction Zone: A place where old
oceanic crust is forced back down into an
ocean trench and back into the mantle

Multiple Choice

What is subduction?

• old crust pushed into mantle

• sea floor spreading

A TRENCH is a deep ocean
canyon. ( Subduction zones are
found here)

Many volcanoes and
earthquakes are found near
subductions zones. (ring of fire)

Evidence of Seafloor Spreading

Fossils

What are some
effects of Plate

Tectonics?

Earthquakes

Earthquakes

1906 and 1989 San Francisco

earthquake was caused by the

movement of tectonic plates at the

San Andreas Fault.

Mountain Building

When two plates collide such a collision
can cause the continental plate to
crumble, and rise upwards – thus forming
mountains.

Multiple Choice

Which type of boundaries produce mountains?

• Divergent

• Continental/Continental Convergent

Volcanoes

• At subduction zones, oceanic plates

dip back down into the hot mantle.

• Heat from the mantle melts the rocks

in the plate, forming magma.

• Magma collects in underground

pockets called magma chambers.

• Hotter than the surrounding rock, the

magma rises to the surface.

Volcanoes

Volcanoes

Hot Spot – place where
magma reaches the surface
of a tectonic plate.

The Hawaiian islands
were formed this way.

Multiple Select

Which 3 types of boundaries produce volcanoes?

• Continental/Continental Convergent

• Oceanic/Continental Convergent

• Oceanic/Oceanic Convergent

• Transform