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Plate Tectonics


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The Earth is…

2 million years old

30 million years old



How old is the Earth?


• The Earth is thought to be around 4,600 million years old, an almost inconcievable time-span. For the moment, think of it as someone in middle age, 46 years old.

• This person is a late developer. Nothing at all is known about their first seven years and only sketchy information exists until about the next 35 years. It is only at the age of 42 that the Earth began to flower.

• Dinosaurs and the great reptiles did not appear until a year ago, when this planet reached 45. Mammals arrived only eight months ago.In the middle of last week, human-like apes evolved into ape-like humans, and at the weekend the last ice age enveloped the earth.

• Modern humans have been around for four hours. During the last hour we discovered agriculture. The industrial revolution began just a minute ago.


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) - 0.0001 m

You were born! – 0.00013 m

First flowers appear – 100 m

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

(figures are in ‘millions of years ago’)


Cross section of the Earth


Continental drift


Evidence for plate tectonics

1. Study of fossils – similar fossils are found on differentcontinents. This is evidence that these regions were once very close or joined together.

3. Shape of continents fit together like a jigsaw.

Africa

SouthAmerica

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


NS S S SS N N N N N

constructivemargin

pattern same both sides

The reversal of the Earth’s magnetic field is recorded in the rocks that solidify at constructive margins. The symmetry around the margin is evidence that the rocks are moving apart.

4. Magnetic field pattern in iron containing rocks

Evidence for plate tectonics



Why do the plates move?

Convention Currents

Mantle

Crust


Plate Names

African Plate

Indo Australian Plate

North American

South American

Eurasian

Pacific

Nazca

Antarctic


Plate Boundaries Can you name plates A and B?

A

B

African Plate

Indo Australian Plate


Plate boundaries


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 at this type of boundary. 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


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

The 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?


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 2 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 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 Boundary



Outer core

Crust

Mantle

Inner core

Attach labels to the correct part of the diagram.


Name this plate boundary

Continental crust MantleThe oceanic crust melts and risesExplosive volcanoes

Oceanic plate

The oceanic crust sinks under the less dense continental crust Earthquakes occur due to friction

Match the labels to the letters

A B

C D

E

F

G


Constructive plate boundaries

Ocean

Oceanic Crust

Mantle

MID OCEAN RIDGE

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

AB

© Boardworks Ltd 2003 1 of 26 Plate Tectonics. © Boardworks Ltd 2003 2 of 26 Most slides contain notes to accompany the presentation. This icon indicates.

Documents

earth slide

powerpoint slide

years old

plate tectonics

continental drift slide

plate boundaries

rocks evidence

millions of years