3.  Understanding Earth’s Interior can be a complicated process.  It’s thick, hot and we don’t have the technology to dig to the core or even through the crust!!!  So how have scientists been able to determine the composition of our Earth?

4. 1. Geologists use seismic waves to study Earth's interior 2. Seismic waves are vibrations that travel through Earth carrying the energy released during an earthquake.  Geologists record the seismic waves and study how they travel through Earth.

5.  The speed of these seismic waves and the paths they take reveal how the planet is put together.

7.  Earth's interior is made up of several layers.  Each layer surrounds the layers beneath it, much like the layers of an onion.

8.  If you really could travel through Earth's layers all the way to the center, what would your trip be like?

9.  At first, the surrounding rock is cool.  At about 20 meters down the surrounding rock gets warmer.  For every 40 meters that you descend from that point, the temperature rises 1 Celsius degree.  This rapid rise in temperature continues for several kilometers.

10. 3. The deeper you go, the greater the pressure. 4. Pressure is the force pushing on a surface or area.  Because of the weight of the rock above, pressure inside Earth increases as you go deeper.

11.  As you go toward the center of Earth, you travel through several different layers. 5. Four main layers make up Earth's interior: a)the crust b)the mantle c)the outer core d)The inner core

12. 6. The crust is a layer of rock that forms Earth's outer skin.  On the crust you find rocks and mountains.  Crust also includes the soil and water that cover large parts of Earth's surface.  Crust includes both dry land (continental) and ocean floor (oceanic).  It is thinnest beneath the ocean and thickest under high mountains.  The crust ranges from 5 to 40 kilometers thick.

14.  Oceanic crust consists mostly of dense rocks such as basalt. Continental crust, the crust that forms the continents, consists mainly of less dense rocks such as granite.

15. 7. Below the crust is the solid material of the mantle, a layer of hot rock.  The crust and the uppermost part of the mantle are very similar. 8. The uppermost part of the mantle and the crust together form a rigid layer called the lithosphere. ◦ In Greek, litho means “stone.” ◦ The lithosphere averages about 100 kilometers thick.

16. 9. The lithosphere floats on top of the asthenosphere.  Beneath the asthenosphere, solid mantle material extends all the way to Earth's core.  The mantle is nearly 3,000 kilometers thick.

17. 10. In general, temperature and pressure in the mantle increase with depth.  The heat and pressure make the part of the mantle just beneath the lithosphere less rigid than the rock above. 11. This soft layer of the mantle is called the asthenosphere ◦ In Greek, asthenes means “weak.” ◦ The asthenosphere is soft. ◦ The material in this layer can flow slowly.

18. 12. Earth's core consists of two parts—a liquid outer core and a solid inner core.  The metals iron and nickel make up both parts of the core.  The outer and inner cores make up about one third of Earth's mass, but only 15 percent of its volume.  The inner and outer cores together are just slightly smaller than the moon.

19. 13. The outer core is a layer of molten metal that surrounds the inner core.  In spite of enormous pressure, the outer core behaves like a thick liquid. 14. The inner core is a dense ball of solid metal.  In the inner core, extreme pressure squeezes the atoms of iron and nickel so much that they cannot spread out and become liquid.

21.  Currents in the liquid outer core force the solid inner core to spin at a slightly faster rate than the rest of the planet. 15. These currents in the outer core also create Earth's magnetic field, which causes the planet to act like a giant bar magnet.