Layers of the Earth s Interior

Transcription

1 Layers of the Earth s Interior 1

2 Focus Question How is the Earth like an ogre? 2

3 Objectives Explain how geologists have learned about the interior of the Earth. Describe the layers of the Earth s interior. Explain the formation of Earth s layers. Describe the Earth s magnetic field. 3

4 5 Minute Activity You have been provided with three canisters. Each contains a different material. Try to determine what is inside each canister even though you can t directly observe what it contains. You may tap, roll, shake, or weigh them. What differences do you notice between the canisters? Apart from their appearance on the outside, are the canisters similar in any way? How did you obtain this evidence? 4

5 Five Minute Activity Based on your observations, what can you infer about the contents of the canisters? How do you think scientists gather evidence about the earth s interior? 5

6 Seismic Waves When an earthquake occurs, seismic waves travel out in all directions through the Earth s interior. 6

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8 Seismic Waves The velocity at which seismic waves travel through a material depends on the material s properties such as composition, mineral phase, temperature, density, and pressure. 8

9 Seismic Waves For example, seismic waves travel faster through denser materials so they tend to speed up with depth. Heat slows down seismic waves. Some seismic waves travel slower through liquids. Other seismic waves do not travel through liquids. 9

10 Seismic Waves When seismic waves pass between geological layers with differing properties resulting in a changed velocity, reflection, refraction (bending) and the production of new waves can occur. Sudden changes in the velocity of seismic waves indicates boundaries between layers with differing properties. 10

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12 Seismic Waves A study of the speed and paths of seismic waves has lead geologists to conclude that Earth is made of layers with different properties. 12

13 Checkpoint What kind of indirect evidence to geologists use to study the structure of the earth? 13

14 Layers of the Earth Scientists think about the Earth s layers in two different ways by their composition and by their physical properties. 14

15 The Composition of the Earth Based on composition, the Earth is divided into three main layers: the crust, the mantle, and the core. 15

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18 The Crust A layer of rock that forms the Earth s outer skin. On the crust you find rocks, mountains, soil, and water. 18

19 The Crust Includes both dry land and the ocean floor. Ranges from 3 62 miles (5-100 km) thick. Thinnest beneath the ocean Thickest under high mountains 19

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21 The Crust Ocean crust consists of more dense rocks like basalt. Continental crust consists mainly of less dense rocks such as granite. 21

22 The Crust Ave. Density g/cm 3 22

23 The Mantle Materials: mainly rock, similar in composition to the mineral olivine, which has large amounts of iron and magnesium compared with other minerals. Density: 4.5 g/cm 3 Thickness: 1802 miles (2900 km) Mostly solid but molten in places. 23

24 The Core Scientists think the Earth s core is made mostly of iron, with smaller amounts of nickel and possibly some sulfur and oxygen. 24

25 The Core Extends from the bottom of the mantle to the center of the Earth. 25

26 The Structure of the Earth The Earth is divided into five main layers based on physical properties. 26

27 The Lithosphere The outermost layer of the earth miles ( km) thick. Made of the crust and the rigid upper part of the mantle. Divided into pieces called plates. 27

28 The Asthenosphere A soft layer of the mantle on which pieces of the lithosphere move. 155 miles (250 km) thick. Made of solid rock that, like putty, flows very slowly (at the rate fingernails grow). 28

29 The Mesosphere Located beneath the asthenosphere 1584 miles (2550 km) thick. Strong lower part of the mantle. Extends from the bottom of the asthenosphere to the core. 29

30 The Outer Core Materials: mainly iron Temperature: 6872 o F (3800 o C) Density: g/cm 3 Thickness: 1367 miles (2634 km) Liquid due to intense heat 30

31 The Inner Core Materials: iron, nickel, and cobalt. Temperature: 7772 o F (4300 o C) Density: 12.5 g/cm 3. Thickness: 808 miles (1300 km) Solid due to the intense pressure at that depth. 31

32 The center of the Earth s core is hotter than the surface of the sun! The temperature of the sun s surface is 9932 o F (5,500 o C). The sun s core temperature, however, is 27,000,032 o F (15,000,000 o C). 32

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34 Checkpoint Why is the inner core solid? 34

35 Layer Formation Scientists believe the earth became molten in its early history.

36 How Did Earth Become Molten? Large amounts of radioactive elements, such as uranium, were probably found in the interior of the earth.

37 Radioactive Elements Elements that break down and change into other elements and give off heat.

38 How Did Earth Become Molten? The heat produced by the breakdown of these buried elements probably melted much of the rock that formed the earth.

39 Layer Formation The heaviest, most dense materials sank and formed the core. Lighter, less dense, rock materials formed the mantle. The lightest, least dense, rock materials floated to the top, cooled, and became the crust.

40 Earth s Magnetic Field The earth has a magnetic field. It protects the Earth from cosmic rays that would strip away the upper atmosphere, including the ozone layer that protects the earth from harmful ultraviolet radiation. (Is this why Mars died?)

41 Earth s Magnetic Field The Earth is like a giant magnet. The north pole of this magnet is near the geographic north pole and the south pole is near the geographic south pole. 41

42 Earth s Magnetic Field Scientists believe the Earth s magnetic field is generated by electrical currents produced by a combination of convective currents and rotation in the liquid outer core. 42

43 Earth s Magnetic Field When you use a compass, the compass needle aligns with the lines of force in Earth s magnetic field. The north-seeking end (south pole) of the compass needle points to Earth s magnetic north pole. (Opposites attract) 43

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46 Checkpoint Why does the earth s density decrease as you move from the core out toward the crust? Why is the inner core solid?

47 Review Explain how the earth may have been formed.

48 Review What are the four main layers of the earth? What is the lithoshere? What is the asthenosphere? What is the mesosphere? 48