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Transcript
How do we know about layers deep within the Earth? Key Points 1. There are many layers of the Earth: A. B. C. 2. Core—inner and outer Mantle Crust—oceanic and continental The uppermost layers are divided into two regions: A. B. Lithosphere Asthenosphere Key Points Continued 3. Earthquakes generate two types of waves: a. b. P Waves S Waves The Structure of the Earth 1. Earth is composed of several layers. CORE: Inner core Densest Iron and nickel Solid- high pressure Hot Outer core Iron and nickel Liquid-lower pressure Heat within the core generates convection currents in the mantle 2. MANTLE: Dense rocky material near the core “Squidgy” near the crust Less dense than the core, more dense than crust Convection currents take place here This is where magma heats up, rises, cools and sinks back down again to heat and start the process over again. 3. CRUST: the outermost and thinnest layer of the Earth. Crust is the thickest at mountain ranges and most thin at the ocean bottoms. Continental Crust: About 22 miles deep under the continents Oceanic Crust: About 6 miles deep under the oceans Lithosphere/Asthenosphere Lithosphere: Includes oceanic/continental crust and the uppermost layer of the mantle up to 100 km below the surface of the Earth. Asthenosphere: Includes the area of the mantle below the Lithosphere. Earth’s Magnetic Field Currently, the Earth’s magnetic pole is located near Earth’s North Pole. This is a condition called normal polarity. Periods when the north magnetic pole is located near Earth’s South Pole are called reverse polarity. When molten lava solidifies at mid-ocean ridges, iron-containing minerals in the lava align themselves with Earth’s active magnetic field. These minerals record the orientation of the magnetic field at the time they solidified. Click here to see a demonstration of Earth’s alternating magnetic polarity. P and S Waves 1. 2. Scientists analyze seismic data (information from eirthquakes) to infer processes that occur inside the planet. Every earthquake generates 2 types of waves: Primary waves (P waves) Secondary waves (S waves) Click here for an example of p and s wave movements. After watching the demo, what do you notice about the speed of the P waves in the land vs. the speed of the S waves in the land? What do you notice about the speed of the P waves in the water? P waves travel faster through the land P waves slow down What do you notice about the speed of the S waves in the water? They can’t travel in liquids Continental Crust vs. Oceanic Crust Continental (40%) Composition Less dense 35-40 km Oldest of the rocks “Floats” on top of mantle Thicker Granite Sedimentary Metamorphic Oceanic (60%) Composition Because of low density it is rarely subducted (recycled) back into the mantle More dense Thinner Mafic rocks Sima 7-10 km Age doesn’t exceed 200 million years Always subducts between oceanic and continental plate boundaries. (recycled back into the mantle) Summary The Earth is made up of several layers—inner and outer core, the mantle, and the crust. The crust is made up of oceanic and continental crust. The lithosphere includes the crust and uppermost layer of the mantle. The aesthenosphere includes the mantle below the lithosphere. The Earth’s magnetic north reverses over time. Summary Continues Scientists study P and S waves to determine the layers of the Earth—s waves travel through solids only, p waves travel through solids and liquids. Since it is not possible to journey to the center of Earth. What must scientists do to infer processes that occur inside the planet? 1. 2. 3. Use drills to drill deep into the layers Study seismic data from earthquakes Use satellites to view images of the layers 33% 1 20 33% 2 33% 3 What are the two types of waves that earthquakes generate? 25% 1. 25% 2. 25% 3. 25% 4. S waves and P waves A waves and B waves R waves and S waves Y waves and X waves 20 Seconds Remaining P waves can… 1. 2. 3. Travel through solids only Travel through liquids only Travel through both solids and liquids 20 33% 33% 33% 1 2 3 S waves can… 1. 2. 3. Travel through solids only Travel through liquids only Travel through both solids and liquids 33% 33% 33% 1 20 2 3 Which statement is true? 1. 2. 3. P waves travel faster through solids than S waves S waves travel faster through solids than P waves P and S waves travel through solids at the same speed 33% 1 33% 2 33% 3 25 How do scientists use P and S waves? 1. 2. 3. To measure the strength of an earthquake To see what layers are solid and what layers are liquid To measure the strength of the core :25 33% 33% 33% 1 2 3