To Understand the structure of the earth through a fully labelled diagram To know the distribution of plates and the difference between continental.

To Understand the structure of the earth through a fully labelled diagram To know the distribution of plates and the difference between continental and oceanic platesDescribe and explain what happens at each of the different plate boundaries

THE RESTLESS EARTH

Learning Objectives

Give me 5 questions…Who? What? Why? Where? When?

The Earth is…

2 million years old

30 million years old

100 million years old

4600 million years old

How old is the Earth?

India collides with Asia – 50 m

Formation of the Alps – 30 m

Dinosaur extinction – 65 m

Man (Homo sapiens) inhabits the Earth – 0.1 m

Industrial Revolution (UK) - 0.00015 m

You were born! – 0.000013 m

First flowers appear – 100 m

Mark the following events on your time line.What do you notice?

(figures are in ‘million years ago’)

4,600 today

million years ago

1,0002,0003,0004,000

History of the Earth

History of the Earth

People (Homo sapiens) only appeared 100,000 years ago!

Big Bang! Dinosaurs die out

Men-like apes Homo sapiens

Cross section of the Earth

The Structure of the Earth

Crust- thin skin of cool rock

Core- a ball of solid iron and nickel. It is surrounded by a large mass of semi- molten rock, which moves very slowly called the mantle.

http://www.bbc.co.uk/learningzone/clips/structure-of-the-earth/9117.html

The Earth’s surface (crust) is divided into tectonic plates

The crust is not one continuous layer but is made up of seven large tectonic plates and many smaller ones (slabs of rock floating on the mantle).

Why do the plates move?

Convention Currents

Mantle

Crust

The Earth’s crust is unstable because the plates are moving in response to rising hot currents called convection currents within the mantle. The movement of the plates has greatest impact, where two tectonic plates meet. The centre of the plates away from the margins, tend to be stable and distant from major tectonic activity.

Plate names

African

Indo-Australian Plate

North American

South American

Eurasian

Pacific

Nazca

Antarctic

Pacific

Can you name plates A and B?

A

BAfrican Plate

Indo-Australian Plate

Plate names

Plate names

There are two types of tectonic plates (crust)

(i) Continental plates (crust)- which is lighter (less dense), thicker about 30km or more, and mostly above sea level

(ii) Oceanic plates (crust)- which is heavier (more dense), thinner about 5km, and mostly below sea level.

a plate boundary or margin. The centre of the plates away from the margins, tend to be stable and distant from major tectonic activity.

The movement of the plates has greatest impact, where two tectonic plates meet, known as

Earthquakes

- Earthquakes occur in long narrow bands, mainly along plate boundaries at all 3 types: destructive, constructive and conservative

- E.g. of earthquakes at a destructive boundary with Nazca plate being subducted under the South American

- Occur in linear clusters- Occur on the land and in the sea- Largest belt runs around the Pacific Ocean where there

is clustering around the edge of the Pacific plate- Other major belts travel along the middle of the Atlantic

Ocean and through the continents of Europe and Asia from the Atlantic to the Pacific Ocean

Distribution of earthquakes and volcanoes

- Volcanoes occur in long, narrow bands- Many volcanoes are found around the Pacific Ocean e.g.

Pacific Ring of Fire- There is a line of volcanoes running down the middle of

the Atlantic Ocean- There are no volcanoes in Australia- Volcanoes are found both on the land and in the sea- Found at constructive and destructive boundaries- Nearly all the volcanoes on the land are sited close to

the oceans

Alaska

Linear (1)Near coast (1)At the plate boundaries (1)Clustered (1)Mainly in western USA and Alaska (1)

Describe the distribution of earthquakes in 4a

Distribution of earthquakes and volcanoes

1) Name the tectonic plate on which Australia is located on Figure 4b

2) Describe the distribution of active volcanoes on Figure 4b (3 marks)

1) Name the tectonic plate on which Australia is located on Figure 4b

Indo-Australian plate

2) Describe the distribution of active volcanoes on Figure 4b (3 marks)

• in a ring around the Pacific• on plate boundaries• odd ones not on plate boundary• clusters on the margins of continents• none in Australia

Explain why the global distribution of volcanoes is so uneven (3)

Uneven because they occur at plate boundaries (1),plate boundaries are linear hence lines of volcanoes(1), plate boundaries often close to continentalmargins (1), destructive margins (1), constructivemargins in mid-ocean (1).

There are three different types of plate movement:

1) Some plates move towards each other (convergent or destructive) e.g. Nazca and South American plates

2) Some plates move away from each other (divergent or constructive) e.g. Nazca and Pacific plates.

3) Some plates slide past each other (conservative or transform) e.g. Pacific and North American plate.

The plates meet at plate boundaries or plate margins, which are areas of great crustal stress. These meeting points are where most of the world’s earthquakes and volcanoes and other structural features, such as fold mountains, rift valleys and ocean trenches.

At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface the volcano does not erupt with much force.

Earthquakes are also found at constructive boundaries.

An example of a constructive boundary is the Mid-Atlantic Ridge.

Constructive plate boundary

Constructive plate boundary

At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface the volcano does not erupt with much force.

Earthquakes are also found at constructive boundaries.

An example of a constructive boundary is the Mid-Atlantic Ridge.

Constructive plate boundary

Constructive margins

Two (continental) plates moving apart as a result of convection current in the Earth’s crust that determine the direction of movement. Some plates like the North American and Eurasian plates, are moving in opposite directions, away from each other. This type of movement mostly happens under the oceans. As the plates move apart, the ‘gap’ is filled by magma rising up from the mantle below, and plugs the gap and cools and creates new crust. As this occurs again and again, layers of lava solidify to create volcanoes. The rising magma creates shield volcanoes which, if they become high enough, form volcanic islands, such as Iceland. So much magma poured out that the ridges are built up from the sea bed, like the Mid-Atlantic ridge, upon which Iceland is located.

Sea Floor Spreading!

Did you know that the ocean floor in the

Atlantic is growing by 3cm per year?

Which of the following pairs of continents are moving further away from each other?

1)Europe and Africa

2)Europe and North America

3)South America and North America

Mid-Atlantic ridge

6 metres 36 metres 928 metres200 metres

Tectonic plates move at different rates.

The Nazca and Pacific plates are moving apart at a rate of 18cm per year while the Eurasian and North American plates are moving apart at a rate of 3cm per year.

To the nearest metre, how far will the Nazca and Pacific plates have moved over the next 200 years?

How fast do plates move?

Constructive plate boundaries

ocean

oceanic crust

mantle

mid-ocean ridge

Where would you find older rocks – at A or at B?

AB

A destructive plate boundary is found where a continental plate meets an oceanic plate.

The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano.

Destructive plate boundary

Destructive margins are where two plates move towards each other e.g. along the West Coast of Japan.

Where an oceanic plate e.g. Nazca meets a continental plate e.g. South American plate the Nazca plate is forced to sink below the South American plate because it is denser. The oceanic crust sinks into the subduction zone, forming an oceanic trench. Energy builds up in the subduction zone- at certain times this may be released as an earthquake. The molten rock called magma, may rise upwards, causing volcanic eruptions and leading to the creation of composite volcanoes.

The lighter continental crust stays at the surface but sediment becomes crumpled into fold mountains. The Andes are the fold mountains that have formed along the West Coast of South America.

Describe the landforms A and B

A = Ocean trench (1), deep (1), narrow (1).

B= Subduction zone (1), area of crustal melting (1),lots of earthquakes triggered (1), Benioff zone (1).

Destructive plate boundary

Collision boundaries occur when two plates of similar densities move together (i.e. a continental plate and a continental plate). This causes the material between them to buckle and rise up, forming fold mountains.

The Himalayas are an example of a chain of fold mountains. They have been formed by the African plate colliding into the Eurasian plate.

Collision plate boundary

Collision plate boundary

Conservative plate boundaries exist where two plates do not directly collide but slide past each other along a fault (weakness).

No volcanoes are found along these plate boundaries, but earthquakes do occur.

An example of such a boundary is the San Andreas Fault in California.

Conservative plate boundary

Conservative plate boundary

Conservative plate margins

Conservative margins are where two plates are moving sideways past each other, or are moving in the same direction but at different speeds.

At the San Andreas fault in California, the North American plate and the Pacific plate are sliding past each other. They are moving in the same direction but the North American plate is moving slightly faster. Pressure builds up along the fault until one plate jerks past each other, causing an earthquake. The movement has also caused the land to become ridged and crumpled. (see image below)

The San Andreas fault, which passes through San Francisco Bay where 7 million people live

http://www.bbc.co.uk/learningzone/clips/understanding-earthquakes-and-plate-tectonics/5724.html

http://www.gatm.org.uk/?p=134

http://www.gatm.org.uk/?p=130

Destructive clip

Constructive clip

http://www.gatm.org.uk/?p=121

Conservative clip

http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/tectonic_plates_video.shtml