THE RESTLESS EARTH
Learning Objectives
 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 plates
Describe and explain what happens at each of the different plate
boundaries
Give me 5 questions…Who? What? Why? Where? When?
How old is the Earth?
The Earth is…
2 million years old
100 million years old
4600 million years old
30 million years old
History of the Earth
Mark the following events on your time line.
What do you notice?
India collides with Asia – 50 m
First flowers appear – 100 m
Man (Homo sapiens) inhabits the Earth – 0.1 m
Formation of the Alps – 30 m
Dinosaur extinction – 65 m
You were born! – 0.000013 m
Industrial Revolution (UK) - 0.00015 m
(figures are in ‘million years ago’)
4,600
4,000
3,000
2,000
1,000
today
million years ago
History of the Earth
People (Homo sapiens) only appeared 100,000 years ago!
Big Bang!
Dinosaurs Men-like apes Homo sapiens
die out
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?
Crust
Convention
Currents
Mantle
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
North
American
Eurasian
Pacific
Pacific
African
Nazca
South
American
Indo-Australian
Plate
Antarctic
Plate names
Can you name plates A and B?
A
African Plate
B
Indo-Australian Plate
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.
The movement of the plates has greatest impact, where two tectonic
plates meet, known as
a plate boundary or margin. The centre of the plates away from the margins,
tend to be stable and distant from major tectonic activity.
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
Describe the distribution of earthquakes in 4a
Linear (1)
Near coast (1)
At the plate boundaries (1)
Clustered (1)
Mainly in western USA and Alaska (1)
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 continental
margins (1), destructive margins (1), constructive
margins 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.
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 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 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.
Mid-Atlantic ridge
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
How fast do plates move?
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?
6 metres
36 metres
200 metres
928 metres
Constructive plate boundaries
mid-ocean ridge
B
A
ocean
mantle
Where would you find older rocks – at A or at B?
Destructive plate boundary
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 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 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
Conservative 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 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/learningz
one/clips/understandingearthquakes-and-platetectonics/5724.html
http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_ha
zards/tectonic_plates_video.shtml
Destructive clip
http://www.gatm.org.uk/?p=134
Constructive clip
http://www.gatm.org.uk/?p=130
Conservative clip
http://www.gatm.org.uk/?p=121