The Earth’s Structure And Tectonic Processes IB SL

Cross section of the Earth

Breakdown Crust Thin, outer-layer of the earth. It is as thin as the skin of an apple is to its flesh. Mantle Composed mainly of silicate rocks, which contain a lot of magnesium and iron. It extends to a depth of 2900km. Temperatures can reach 5000 degrees Celsius, which generate convection currents. Core Contains iron and nickel. Situated approximately 6371km below the surface. Temperature is around 5500 degrees Celsius.

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

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 Pattern same both sides

Crust Convention Currents Mantle

Plate Tectonic Theory The location of continents today of far removed from what it was millions of years ago, when it is believed that all continents were joined to one land mass. Alfred Wegener put forward a theory regards their movement in 1912 with his theory of Continental Drift. His theory was based on observations such as: Biological: Coal is found in UK but needs warm, wet, humid conditions to form. Observational: The shapes of countries appear to 'fit' one another, for example, S. America and Africa.

Plate Movements In the 1940's-1960's the theory was revised and Plate Tectonic theory emerged. It is based on the premise that the lithosphere (crust and rigid upper mantle) is divided into plates, which are moved by convection currents coming from the earth's core.

2 Types Of Crust Oceanic Crust (Sima) Young (under 200 million years), thin, dense and heavy, will sink. Always being created and destroyed. For example, Basalt. Continental Crust (Sial) Old, light, thick (up to 150km under mountains) permanent, does not sink. For example, Granite.

Plate Margins Movement of plates is in one of 3 ways: Towards each other: Convergent (destructive or collision). Away from each other: Divergent. Alongside each other: Transform or transcurrent. There is a further subdivision for Convergent plates, which is dependent on the properties of the plates moving towards each other (oceanic / continental crust).

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

1) Europe and Africa 3) South America and North America 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 3) South America and North America 2) Europe 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

Convergent Plate Boundaries (Together) The two types of margins that occur here are Destructive Margins or collision Zones... Destructive margins Oceanic crust moves towards continental crust. Oceanic crust sinks, and slowly destroyed. Results in deep ocean trenches, island arcs and fold mountains. Can be referred to as subduction zones. Collision Zones Two continental crusts meet, neither sinks, fold mountains result. For example, the Alps.

Divergent Plate Boundaries (Away) Also known as a Constructive margin. Plates move away from each other, for example, N. American and Eurasian plates, cresting mid-ocean ridges such as the Mid Atlantic Ridge. New material appears at the ocean ridge.

Transcurrent Boundaries (Side-By-Side) Here plates simply move alongside each other, land is neither created nor destroyed. Plates rub against each other causing friction resulting in earthquakes only at these boundaries.

Examples Destructive Plate Margins Peru - Chile Trench as oceanic crust is subducted. Earthquakes, due to the heat created as the Nazca plate is destroyed. Fold Mountains such as the Andes. Volcanoes if heat from the subduction zone has the opportunity to reach the surface, for example, Cotopaxi. Island arcs and volcanic islands, for example, Japan.

Examples Collision Zones Indian Plate and Eurasian Plate created the Himalayas. Constructive Margins North American plate moving away from the Eurasian plate resulting in the mid Atlantic ridge. Transform Faults Earthquakes such as those linked with the San Andreas Fault.

Hot Spots There are examples where volcanic activity is not linked to plate margins as in the case of the Hawaiian Islands. This is believed to be due to the presence of 'hot spots' - places of localised heat under the earth's crust that then find their way to the surface.

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

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

Activity 1 Using Essential AS Geography P31, answer the following… What are the 3 major relief features associated with constructive margins? Create a diagram to show/describe the processes operating at constructive margins. What is “Palaeomagnatism” and how does it explain the idea of sea floor spreading?

Activity 2 Using Essential AS Geography P33-35, answer the following… What is a destructive margin? How are Earthquakes, Volcanoes, Ocean Trenches, and Island Arcs associated with these boundaries? Describe the formation of the Himalayas and explain why there are few earthquakes and no volcanoes there.