TECTONICS

1. TECTONICS What is the structure of the Earth?

3. Introduction

4. Learning objectives • What is the structure of the Earth? • What are Plate Tectonics?

5. Crust (Earths outershell) Solid rock-4-35km thick Mantle 2,900km thick Very Hot – 2500 oC It is like ‘Blu Tack’ Outer Core Very Hot – 4000oc Almost Liquid Solid Inner Core Very Very Hot – 5000oC Made up of Iron and Nickel Structure of the Earth

6. The Story of the Continental Drift…. 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.

7. Evidence for continental drift • Shapes of continents • Some continents fit together like a jigsaw. Africa South America • Study of fossils • Similar fossils are found on different continents. • This is evidence that these regions were once very close or joined together. • Pattern of rocks • Similar pattern of rock layers on different continents is evidence that the rocks were once close together or joined.

8. What is plate tectonics? 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? • 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.

9. Plate Tectonics • The Theory of Plate Tectonics has only been developed in the past Thirty years. • It revolves around the earth’s crust being divided into several large sections, called plates. • Due to the movement of the hot mantle below (convection currents) these plates move around the earth at up to 17 cm per year. Formation of Convection Currents. • Convection currents are produced by the rising of hot material from the mantle and the sinking of the cooler mantle rock nearer the surface. • This results in a circular movement of material.

12. The Earth

13. The Worlds Plates Ex. Pacific Plate Ex. Pacific Plate Task: Download and print the following worksheet: “The World Plates” Label the name of each tectonic plate (ex. “Pacific Plate). There should be 12 labeled plates. Label the direction of the movement of each plates by drawing an arrow (see above for example). Colour each plates differently so you can distinguish each one. Plot at least 10 major volcanic eruptions and 10 major earthquakes in your worksheet. Make sure you use a proper key when completing the worksheet.