• 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

(F.E.E.D)• 3 main theorists and theories• Human interaction

The Earth is made up of 4 main layers:

Inner core• Outer Core• Mantle• Crust

(Lithosphere and the Asthenosphere)

Inner core

Outer core

Mantle

Crust

“Plates” of lithosphere are moved around by the movement of the magma below in the mantle.

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 MeteorologistMaurice Ewing – an American oceanographer/geophysicistHarold 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

Same fossils and rocks found in different parts of the world

Africa and South America look like pieces of a jigsaw

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 Wegeners 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