• 4 Layers of the earth

• 7 main plates of the earth

• 3 main plate boundaries

• 2 types of crust

• 3 main features of plate tectonics

• 3 main theorists and theories

• Human interaction

The Earth is

made up of 3

main layers: • Core

• Mantle

• Crust

(Lithosphere and

the Athenosphere)

Inner core

Outer core

Mantle

Crust

“Plates” of lithosphere are moved around by

the underlying hot mantle convection cells

This is where we live!

The Earth’s crust is made of:

Continental Crust

- thick (10-70km)

- buoyant (less dense

than oceanic crust)

- mostly old

Oceanic Crust

- thin (~7 km)

- dense (sinks under

continental crust)

- young

Plates are

made of rigid

lithosphere.

The lithosphere is

made up of the

crust and the upper

part of the mantle.

Below the

lithosphere

(which makes

up the tectonic

plates) is the

asthenosphere.

Constructive (known as Divergent)

Destructive (known as Convergent)

Transform/Passive/ Neutral/Conservative

Three types of plate boundary

Spreading ridges

• As plates move apart new material is erupted to

fill the gap

Constructive Boundaries

Age of Oceanic Crust

Can you find ICELAND?

ICELAND

Iceland has a divergent

plate boundary running

through its middle

Iceland: An example of continental rifting

There are three styles of

destructive/convergent plate

boundaries • Continent-continent collision

• Continent-oceanic crust collision

• Ocean-ocean collision

Destructive Boundaries

Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

Called SUBDUCTION

Continent-Oceanic Crust Collision

Oceanic lithosphere subducts underneath the continental lithosphere

Oceanic lithosphere heats and dehydrates as it subsides

The melt rises forming volcanism

E.g. The Andes

Subduction

When two oceanic plates collide, one runs over

the other which causes it to sink into the mantle

forming a subduction zone.

The subducting plate is bent downward to form

a very deep depression in the ocean floor

called a trench.

The worlds deepest parts of the ocean are

found along trenches.

• E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

Where plates slide past each other

Neutral / Transform Boundaries

Above: View of the San Andreas

transform fault

If you look at a map of the world, you may notice that some of the

continents could fit together like pieces of a puzzle.

The study of plate tectonics has been furthered by the work

of three main theorists.

Alfred Wegener – a German Meteorologist

Maurice Ewing – an American oceanographer/geophysicist

Harold H. Hess – Professor of Geology, Princeton, USA

In his published work “The origins of continents and

Oceans” (1912) Wegener proposed that millions of years

ago all the continents of the earth were once joined

together in one large land mass called….Pangea

Slowly, due to magma convection currents deep within the

mantle, Pangea broke into two large continents called

Laurasia and Gonwanaland.

Over millions of years these two broke and moved into the

main continents we know today.

Same fossils and

rocks found in

different parts of the

world

Africa and South

America look like

pieces of a jigsaw

Some people thought the Earth was shrinking and cracking

Wegener thought whole sections of the crust moved (plate tectonics)

Some people did not understand and thought the continents floated around in the oceans (continental drift)

He died before people accepted his ideas

Ewing studied and photographed much of the

earths ocean floors. Once, during a trans-

Atlantic flight, he looked down and noticed a

dark shadow running along the Atlantic

Ocean. Research showed that the American

and Eurasian plates were separating and new

crust was forming. Layers and ages of each

new magma flow showed the widening of the

sea floor over millions of years.

Hess was an American professor who furthered the study

of plate tectonics with his theory of Sea Floor Spreading

and the creation of new crust and volcanic ridges.

• Alfred Wegener (1912) – Continental Drift

• Maurice Ewing (1947) – Mid Atlantic Ridge

• Harry Hess (1960s) – Sea Floor Spreading

All combined, plus the study of countless others, creates

the Theory of Plate Tectonics

• Volcanoes

• Earthquakes

• Fold Mountains

Plates moving in any

direction causes

earthquakes

The worst are caused

by plates rubbing

past each other as in

C

This happens along

the Californian coast

Large continents begin to crack and split apart

The gaps fill with water

Small seas become oceans

The mid ocean ridge continues to produce new crust

Why is the Atlantic still getting

wider

The plates are pulled apart by

convection currents in the

mantle below

Caused by heat released from

natural radioactive processes

At the mid Atlantic ridge molten

rock from below rises up to fill

the gap with new basaltic rock

More evidence has been

found for Wegener's theory

The Earths North and South

pole have flipped many

times

These leaves magnetic

‘stripes’ in rock containing

iron minerals

Dense heavy oceanic crust

can be subducted below less

denser continental crust.

The friction melts rock

This magma rises through the

crust to form new volcanoes

This is happening in South

America (The Andes)

Eventually when plates move

together the continental crust

collides

The heat and pressure make

metamorphic rock

It also pushes and folds the

rocks into high mountains

The Himalayas rise to 8848m

and are still growing today

…what’s the connection?

Volcanoes and Plate

Tectonics…

Volcanism is

mostly

focused at

plate

margins

Pacific Ring of Fire

- Subduction - Rifting - Hotspots

Volcanoes are formed by:

Pacific Ring of Fire

Hotspot

volcanoes

Hot mantle plumes breaching the

surface in the middle of a tectonic

plate

What are Hotspot Volcanoes?

Photo: Tom Pfeiffer / www.volcanodiscovery.com

The Hawaiian island chain are

examples of hotspot volcanoes.

The tectonic plate moves over a fixed hotspot forming a

chain of volcanoes.

The volcanoes get younger from one end to the other.

…what’s the connection?

Earthquakes and Plate

Tectonics…

As with volcanoes, earthquakes are not randomly distributed over the globe

At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.

Figure showing

the distribution of

earthquakes

around the globe

Figure showing the tectonic setting of earthquakes

The Earth is made up of 3 main layers (core,

mantle, crust)

On the surface of the Earth are tectonic

plates that slowly move around the globe

Plates are made of crust and upper mantle

(lithosphere)

There are 2 types of plate

There are 3 types of plate boundaries

Volcanoes and Earthquakes are closely

linked to the margins of the tectonic plates