plate tectonics · 2 of 31 © boardworks ltd 2005 how old is the earth? what is the earth made...

© Boardworks Ltd 20051 of 31

These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page.

This icon indicates the slide contains activities created in Flash. These activities are not editable.

For more detailed instructions, see the Getting Started presentation.

1 of 31 © Boardworks Ltd 2005

Plate Tectonics


How old is the Earth?What is the Earth made from?What is Plate Tectonics?What happens at the different types of plate boundary?

Lea

rnin

g o

bje

ctiv

es


The Earth is…

2 million years old

30 million years old

100 million years old4600 million years old

How old is the Earth?


History of 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 – 150 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



Lea

rnin

g o

bje

ctiv

es


Cross section of the Earth



Lea

rnin

g o

bje

ctiv

es


In 1912, a German scientist called Alfred Wegener proposed that South America and Africa were once joined together and had subsequently moved apart.

He believed that all the continents were once joined together as one big land mass called Pangaea and this was intact until about 200 million years ago.

The idea that continents are slowly shifting their positions is called continental drift.

What is continental drift?


Study of fossilsSimilar fossils are found on different continents. This is evidence that these regions were once very close or joined together.

Shapes of continentsSome continents fit together like a jigsaw.

Africa

SouthAmerica

Pattern of rocksSimilar pattern of rock layers on different continents is evidence that the rocks were once close together or joined.

Evidence for continental drift


Continental drift


What is Plate Tectonics?

The Earth's surface is made up of a number of large plates (like pieces of a jigsaw puzzle) that are in constant, slow motion.

The ocean floors are continually moving, spreading from the centre and sinking at the edges.

At the edges of these plates (plate boundaries) earthquakes and volcanoes occur.

Convection currents in the mantle move the plates. The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

Wegener knew the continents had drifted but he couldn't explain how they drifted. It wasn't until the 1960's that geologists used ocean surveys to explain continental drift with the theory of Plate Tectonics.

What is plate tectonics?


Why do the plates move?


African

Indo-Australian Plate

North American

South American

Eurasian

Pacific

Nazca

Antarctic

Pacific

Plate names


Can you name plates A and B?

A

BAfrican Plate

Indo-Australian Plate

Plate names


Plate names



Lea

rnin

g o

bje

ctiv

es


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


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 Americanplates 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?


ocean

mantle

mid-ocean ridge

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

AB

Constructive plate boundaries


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


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 Faultin California.

Conservative plate boundary


Conservative plate boundary


4. continental crust 6. mantle

3. The oceanic crust melts and rises.

5. explosive volcanoes

1.oceanic plate 2. The oceanic crust sinks under the less dense continental crust.

Match the labels to the letters.

AB

CD

E

F



Plate definitions

plate tectonics · 2 of 31 © boardworks ltd 2005 how old is the earth? what is the earth made...

Documents