Chapter 28

1. Chapter 28 THE CHANGING EARTH

2. The Layers of Earth

3. The Layers of Earth • Crust- a thin surface covering the Earth. • 2 kinds: Oceanic & Continental • What is a crack in the crust called?? • Mantle- a thick molten layer between the core and the crust • Outer Core- molten iron, nickel, and oxygen • Inner Core- solid iron and nickel • The core’s temperature ranges between 2,000 oC and 5,000 oC…hot, hot, hot!

4. Is there a pattern??? YES!!! The Surface of Earth

5. Continental Drift • The idea that the continents were once one landmass; a “super-continent” named Pangea • How is this possible?

6. mantle convection Heat transferred from the core to the mantle produces a slow convection of the material in the mantle • Thermal Convection Demo

7. Sea Floor Spreading • Mid-Ocean Ridges: mountain ranges on the ocean floor • The closer you get to a ridge, the younger the ocean floor. • Scientists concluded that the “new” land must be coming up through the ocean ridges

8. The Theory Of Plate Tectonics • Explanation of how continents move • Earth's outer layer is made up of tectonic plates, which are moving • explains the how and why behind mountains, volcanoes, and earthquakes • What is the area called where 2 plates meet?

9. Plate Boundaries

10. Divergent Plates • Plates are moving apart, allowing molten material to rise up and create new crust • Mid-ocean ridges • Sites of earthquakes and volcanoes

11. Convergent Plates • Occurs when two plates approach each other • Subduction: one plate slides under another • Often the site of volcanoes • Collision can also occur between approaching plates • Mountains form

12. Convergent Plates • Subduction: • Collision:

13. Transform Plates • Occurs when 2 plates slide past each other • No crust is created or destroyed • Earthquakes • What “famous” transform plate boundary is located in the US?

14. Review of Boundaries

15. Facts & Figures: Earthquakes • Largest EQ recorded in the US: 9.2 • Largest in world: 9.5 • 500,000 detectable EQ’s each year. • More damage is caused indirectly from the EQ, not the EQ itself. • 10,000 EQ’s will develop in southern California this year. However, most will not be felt • Powerful EQ’s rocked the Midwest in the 1800’s. One recorded a magnitude of over 8 and caused church bells to ring in Boston Massachusetts • Deadliest EQ: China in 1557, killing 830,000 people

16. Earthquakes • Vibrations of the earth’s crust from the movement of plates along faults • As plates move, they stretch/compress, and stress builds up • When the rocks break or change shape, they release stored energy in the form of movement • LIKE A RUBBER BAND! • This creates seismic waves that move through Earth

18. Seismic Waves • Body Waves • originate from the center of an EQ • 2 kinds: • P waves & S Waves • Surface Waves – Move along the surface of the Earth

19. Measuring Earthquakes • Richter scale: • Related to the amplitude of the seismic waves • More accurate for earthquakes that are near • Mercalli scale: • Uses 12 descriptive categories that describe the damage caused by earthquakes

20. Where do Earthquakes Occur? • Along plate boundaries, faults

21. Earthquakes in the US:SAN ANDREAS FAULT • A well known transform boundary where the Pacific plate and North American plate meet • Average rate of motion across the San Andreas Fault is 2 in./yr. (3 million years L.A. will be next to S.F.)

22. Do EQ’s occur anywhere else in the US? YES!...it’s been a while, but there are other fault lines in the US. New Madrid fault in Midwest 250 miles long Last major EQ in 1895 Eastern US Last major EQ in 1886 Why would an EQ be so damaging in these areas today? Earthquakes in the US:OTHER FAULT LINES