1. GEOPHYSICAL CH 17: EARTH STRUCTURE

2. The Layers of the Earth © Copyright 2006. M. J. Krech. All rights reserved.

3. THE FOUR LAYERS The Earth is composed of four different layers. The crust is the layer that you live on, and it is the most widely studied and understood. The mantle is much hotter and has the ability to flow. The outer core and inner core are even hotter with pressures so great you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!

4. EARTH LAYERS The Earth is divided into four main layers. *Inner Core *Outer Core *Mantle *Crust - lithosphere -asthenosphere

5. THE CRUST *The Earth’s crust is like the skin of an apple. It is very thin compared to the other three layers. *The crust makes up 1% of the Earth. * The crust is made of the lightest matter and the core consists of heavy metals

6. THE CRUST The crust is only about 3-5 miles (8 kilometers) thick under the oceans ( oceanic crust ) and about 25 miles (32 kilometers) thick under the continents ( continental crust ).

7. THE CRUST The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates.

8. THE LITHOSPHERE The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere. This rock is divided into fragments plate.

9. WHAT IS THE THEORY OF PLATE TECTONICS? Tectonic plates: a theory that giant plates of rock are moving slowly across Earth’s surface

10. THE LITHOSPHERIC PLATES The crust and upper portion of mantel (lithosphere) of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere.

11. ASTHENOSPHERE The plates move along the soft mantle which is the layer located below the crust.

12. LITHOSPHERE AND ASTHENOSPHERE The lithosphere (litho:rock; sphere:layer) is the strong, upper 100 km of the Earth. The lithosphere is the tectonic plate we talk about in plate tectonics. The asthenosphere (a:without; stheno:strength) is the weak and easily deformed layer of the Earth that acts as a “lubricant” for the tectonic plates to slide over. The asthenosphere extends from 100 km depth to 660 km beneath the Earth's surface. Beneath the asthenosphere is the mesosphere, another strong layer.

13. The Asthenosphere The asthenosphere is the semi- rigid part of the middle mantle that flows like hot asphalt under a heavy weight.

14. PLATE TECHTONICS The plates move along smoothly but sometimes they get stuck and pressure builds up.

15. EARTHQUAKES The pressure builds and causes an Earthquake as rocks break and crack. San Francisco City Hall after the 1906 Earthquake. (from Steinbrugge Collection of the UC Berkeley Earthquake Engineering Research Center)Steinbrugge Collection of the UC Berkeley Earthquake Engineering Research Center

17. THE MANTLE The mantle is the layer below the crust. The mantle is the largest layer of the Earth. The mantle is divided into two regions: the upper and lower sections.

18. MANTLE The movement of the mantle create the movement of the Earth’s plates. It is made of hot, dense rock. The rock in the mantle flows like asphalt because of the temperature differences found in the mantle.

19. CONVECTION CURRENTS The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

20. CONVECTION CURRENTS The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration.

21. CORE The core of the Earth is much like a ball of very hot metals. The inner core is surrounded by a fluid iron outer core.

22. CORE

23. OUTER CORE * The core of the Earth is like a ball of very hot metals. * The outer core is liquid. * The outer core is made up of iron and is very dense.

24. INNER CORE * The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move. * The inner core is a solid.

25. REVIEW 1) What are the four layers of the Earth? 2) The Earth’s crust is very ______? 3) The mantle is the largest layer of the Earth? True or False 4) Is the Outer Core a liquid or a solid?

26. ANSWERS! 1) Crust, Mantle, Outer Core, Inner Core 2) Thin 3) True 4) Liquid

27. WHY DO WE NEED TO KNOW THIS? Earth has layered structures with solid rock at the surface and partly liquid rock material below. When scientists understand the Earth’s structure, they can help predict when a geyser or a volcano will erupt, or how a river will change course over time.

28. DID YOU KNOW? In many parts of the world, columns of steaming hot water can be found shooting up from the Earth’s surface. These boiling fountains are known as geysers!!! Jim Bridger was Quoted as saying the geysers are so hot that meat is readily cooked in them!!

29. DID YOU KNOW? Yellowstone National Park in Wyoming is well known for its numerous geysers and hot springs.

30. OKAY, BACK TO GEYSERS… What do geysers tell us about the Earth’s interior?

31. GEYSERS TELL US THE EARTH’S INTERIOR IS… HOT, HOT, HOT!!!

32. THE DEEPER INTO THE EARTH’S INTERIOR YOU GO, THE HOTTER IT GETS!!!

33. SO, IS IT HOTTER AT THE EARTH’S CORE, OR THE EARTH’S CRUST? - CORE, MANTEL, OR CRUST?

34. LET’S THINK… Where would be the best place on Earth’s surface to try to drill a hole all the way to the mantle? (Remember, the mantle is the thickest layer between the crust and the outer core.) A.The ocean floor B.The top of a mountain

35. THE OCEAN FLOOR The crust is thinner under the ocean, making it easier to drill a hole to the mantle. Why would it be most difficult to drill a hole to the mantle starting at the top of a mountain?

36. ANSWER The crust is thickest at the top of a mountain. (Think of it this way… if you start drilling at the top of a mountain you must drill all the way down through the mountain just to get to ground level. Then, you have to continue drilling until you hit the ocean floor. Only then does the actual drilling below the Earth’s crust begin.

37. QUESTION What layer of the earth’s core is liquid?

38. ANSWER Outer core!!! The heat there is hot enough to melt rock, but the pressure is not great enough to make a solid mass, as it is in the inner core.

39. UP NEXT!!! Next, we’ll study plate tectonics, volcanoes and earthquakes!!!