1. 1 Hi Guys This term we have 2 more units: Changing Earth Working world For the next 6 weeks it is ‘Changing Earth’

2. 2 What is Changing Earth all about? To start with, we will look at the structure of the earth, and in particular, those parts that are implicated in earthquakes. The next 2 weeks will be looking at what they are, how they form, what it is like to live through them. After that we will look in a bit of detail as to what and how changed the shape of the earth’ surface. Having established, the what and the how, we will then look at coasts, how the features form and some of issues about the changes that occur naturally, but which do not make the people nearby that happy! I am hoping that as part of this last section, you will be able to persuade your parents to take you on a trip to the seaside to take a picture or 2! It will be official homework by the way.

3. 3 What is the Earth made of? Mud and stones and water?

4. 4 The Structure of the Earth A thin crust - 10- 100km thick and not very dense A mantle – extends almost halfway to the centre, hot and dense A core – made of molten nickel and iron. Outer part is liquid and inner part is solid. Gets hot due to radioactive decay. The Earth is believed to be 4500 million years old

5. 5 The structure of the earth inner core The inner core is in the centre of the earth and is the hottest part of the earth. The inner core is solid. It is made up of iron and nickel with temperatures of up to 5500°C. With its immense heat energy, the inner core is like the engine room of the Earth. outer core The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot here, with temperatures similar to the inner core.

6. 6 The structure of the earth mantle The mantle is the widest section of the earth. It has a diameter of approximately 2900km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down, nearer the inner core, the rock is soft and beginning to melt. crust The crust is the outer layer of the earth. It is a thin layer between 0-60km thick. The crust is the solid rock layer upon which

7. 7 Now this is what is happening inside the Earth

8. 8 Plates and plate boundaries The earth's crust is broken up into pieces. These pieces are called plates. Heat rising and falling inside the mantle creates convection currents. The convection currents move the plates. The movement of the plates, and the activity inside the earth, is called plate tectonics. Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries.

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12. 12 Boundaries between tectonic plates can be of four types: 1. Constructive plate boundaries move apart and create new crust, and often give rise to volcanoes and earthquakes. 2. Destructive plate boundaries move towards each other and the heavier oceanic plate slides under the lighter continental plate 3. Conservative plate boundaries move past each other and do not create or destroy land, but often give rise to earthquakes (not volcanoes). 4. Collision plate boundary where 2 continental plates move towards each other and both are pushed upwards to make mountains

13. 13 What happens at a constructive plate margin?

14. 14 Constructive Plate Margin At a constructive boundary the plates are moving apart due to convection currents inside the earth. The Eurasian and North American plates moving away from each other – so very slowly Europe is getting further away from America. As the plates move apart (very slowly), magma rises from the mantle. The magma erupts to the surface of the earth. When the magma reaches the surface, it cools and solidifies to form a new crust of rock. This process is repeated many times, over a long period of time. Eventually it forms a volcano.

15. 15 Constructive Plate Boundary Constructive boundaries tend to be found under the sea, e.g. the Mid-Atlantic Ridge. Here, chains of underwater volcanoes have formed. Some of these volcanoes get so large that they erupt out of the sea to form a volcanic island, like Volcano Helgafjell on the Westman Islands near Iceland.

16. 16 What happens at a destructive margin?

17. 17 Destructive Plate Margin At a destructive boundary the plates are moving towards each other. This is usually a continental plate (a plate carrying land) and an oceanic plate (a plate carrying ocean). The oceanic plate is denser than the continental plate so, as they move together, the oceanic plate is forced underneath the continental plate. As the oceanic plate is forced below the continental plate it melts to form magma. This magma then rises up through cracks in the continental crust. As pressure builds up, a volcanic eruption may occur. An example of this is where the Pacific plate is pushing under the South American plate to form the Andes.

18. 18 Collision Plate margin Collision Plate margin Continental plate Pushing against Continenta l plate They are both the same density – so they push up their edges against each

19. 19 Collision plate margin Continental crust is squashed together with another continental crust and they are both forced upwards. This is called folding. The process of folding creates fold mountains. Fold mountains can also be formed where two continental plates push towards each other. This is how the Himalayas were formed No – none here! Any volcanoes?

20. 20 What happens at a conservative margin? At a conservative boundary the plates are sliding horizontally past each other. No land is created at a conservative boundary and none is destroyed. Volcanoes do not occur along these boundaries but earthquakes are very common. A very well-known example of a conservative boundary is the San Andreas Fault, which runs through the state of California in the USA.

21. 21 If the plates are moving, were the continents always where we see them today? No and there is lots of evidence for this The process is called continental drift Evidence for this: 1. Mountain chains match up 2. Fossils match up 3. The continents fit together like a jigsaw (not perfect because of erosion!)

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24. 24 Continental Drift

25. 25 Continental Drift

26. 26 Continental Drift

27. 27 Continental Drift