Plate Tectonics

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How old is the Earth? The Earth is… 2 million years old

(figures are in ‘millions of years ago’) Mark the following events on your time line. What do you notice? First flowers appear – 100 m India collides with Asia – 50 m Man (homo sapiens) inhabits the Earth – 0.1 m Formation of the Alps – 30 m You were born! – 0.00013 m Dinosaur extinction – 65 m Industrial Revolution (UK) - 0.0001 m (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 different continents. This is evidence that these regions were once very close or joined together. 2. Pattern of rocks – similar pattern of rock layers on different continents is evidence that the rocks were once close together or joined. 3. Shape of continents fit together like a jigsaw. Africa South America

Evidence for plate tectonics 4. Magnetic field pattern in iron containing rocks 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. constructive margin N S N S S S N N N N S pattern same both sides

Why do the plates move? Crust Convention Currents Mantle

Plate Names Eurasian North American Pacific African Plate South American Indo Australian Plate Nazca Antarctic Plate Names

A B Plate Boundaries Can you name plates A and B? African Plate Indo Australian Plate B Plate Boundaries Can you name plates A and B?

Plate boundaries link 1 link 2

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

Constructive plate boundary link 1 link 2 link 3 link 4

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? Europe and Africa Europe and North America South America and North America

How fast do plates move? 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? 6 metres 36 metres 200 metres 928 metres

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 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 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

Attach labels to the correct part of the diagram. Outer core Crust Mantle Inner core

Name this plate boundary G A B E F D C Match the labels to the letters The oceanic crust sinks under the less dense continental crust Earthquakes occur due to friction Oceanic plate The oceanic crust melts and rises Mantle Continental crust Explosive volcanoes

Constructive plate boundaries MID OCEAN RIDGE A Ocean B Oceanic Crust Mantle Where would you find older rocks – at A or at B?