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Movements of the Earth’s Crust Continental Drift Alfred Wegener proposed the hypothesis of continental drift The idea the continents were all together at one point and drifted to their present locations Pangaea: Name of all land masses Panthalassa: Water surrounding Pangaea Pangaea What is the Evidence? Similarities of the coastlines Fossils of plants and animals in parts of Pangaea that had been joined Types of rocks and rock layers on the coastal region of formerly adjoined parts Changes in climate patterns Glacier Records Fossil Evidence Rock Similarities Coastline Similarities Theory of Plate Tectonics Plate Tectonics There are two types of crust- oceanic and continental There are 30 plates on the earth’s surface The plates are chunks of lithosphere that float on the asthenosphere Lithosphere: Crust and the upper mantle Asthenosphere: Layer of plastic rock Rules of Plate Tectonics 1. Continental crust is less dense, or lighter, than Oceanic crust so it doesn't sink. It is never destroyed and is permanent. 2. Oceanic crust is heavier so it can sink below Continental crust. It is constantly being formed and destroyed at ocean ridges and trenches. 3. Continental crust can carry on beyond the edges of the land and finally end far below the sea. This explains why the edges of all the continents don't have deep trenches right up against their coastlines. 4. Plates can never overlap. This means that they must either collide and both be pushed up to form mountains, or one of the plates must be pushed down into the mantle and be destroyed. Rules of Plate Tectonics Continued… 5. There can never be gaps between plates, so if two plates move apart, as in the middle of the Atlantic, new rock will be formed to fill the space. 6. We know the Earth isn't getting bigger or smaller, so the amount of new crust being formed must be the same as the amount being destroyed. 7. Plate movement is very slow. This is partly why Wegener's original ideas were ignored. Nobody could 'see' the continents moving. When the plates make a sudden movement we call it an Plates of the World Types of Crust Crust: very thin outer layer of the earth Oceanic crust is more dense, heavier, and younger than continental crust Types of Plate Boundaries *Draw these pictures in your notes* Diverging Plate Boundary • In most cases, there is seafloor spreading occurring at this type. Two plates moving away from each other, Molten Rock, from the asthenosphere, move up to fill the gaps between the 2 plates and form new crust. Rift Valley: Narrow valley formed when plates are separating Diverging Boundary Seafloor Spreading Rift Valley Convergent Plate Boundaries • Two plates colliding and one is being subducted under another. –Subduction Zone: one plate moving under another –Ocean Trench: generally forms along a subduction zone –Mountain Ranges –Island Arc: chain of volcanic islands Converging Boundary Oceanic-Oceanic Converging Oceanic-Continental Converging Continental-Continental Converging Transform Plate Boundary • Two plates grinding past each other. Earthquakes occur here. Transform Plate Boundary What Causes Plate Motion? Most think that the major reason for plate movement is due to convection. Convection Current: formed by hot rock formed in the asthenosphere rising and the cold material at the surface falling to replace the rising material. Plates float along this heated flowable material. Convection Currents Compositional Layers of the Earth Crust Mantle Outer Core Inner Core Mechanical Layers of the Earth Lithosphere Asthenosphere Mesosphere Outer Core Inner Core Earthquakes A. B. C. D. When rock fragments move, they release energy in the form of seismic waves. The point where the earthquake occurs is called the focus. The point on the surface that is directly above the focus is the epicenter. Most earthquakes have a shallow focus because other focuses loose energy before it reaches the surface. ANSS Recent Earthquakes in the US Three major earthquake zones Pacific Ring of Fire West coast of north/south America Along here, most plates are being subducted or scrape past each other. Mid-Oceanic Ridge Spreading motion creates stress in the rocks along the mid-oceanic ridges. Seafloor spreading –Mid-Atlantic Ridge: under sea mountain range with a steep narrow valley running down the center. –Part of a mid-oceanic ridge that winds its way around earth. –New rock is forming at the oceanic ridges and is called seafloor spreading. Eurasian-Melanesian Belt: Formed with the collision of Eurasian and Africa and Indian plates. The mountains are being produced at boundaries. these Potential Earthquakes in US Recorded Earthquakes Around The World Earth/ Env Sci Please get your notes out and something to write with. You should ALL be in your seats, ready to go when the bell rings. We have notes to take first, then a guided worksheet, then our test review. *TEST MONDAY!!! Fault Zones Created when the plates separate, collide, subduct, and slide past each other. Example: San Andres fault in California. Earthquakes can also occur along former fault lines in the middle of current plates. What is a Fault? Faults are fractures in Earth's crust where rocks on either side of the crack have slid past each other 3 Types of Faults Strike-slip faults indicate rocks are sliding past each other, with little to no vertical movement. Both the San Andreas and Anatolian Faults are strike-slip. Normal faults create space. Two blocks of crust pull apart, extending the crust. The Basin and Range Province in North America and the East African Rift Zone are two well-known regions where normal faults are spreading apart Earth's crust. Reverse faults, also called thrust faults, squeeze the crust, pushing two blocks of crust on top of each other. These faults are commonly found in mountain ranges such as the Himalayas and the Rocky Mountains. Faults Recording Earthquakes Earthquakes are recorded by an instrument called a seismograph Every earthquake is going to give off three different seismic waves To find the location of an earthquake readings from three different locations are needed Types of Seismic Waves P Waves: the fastest moving wave and can travel through solids and liquids S Waves: Can only travel through solids and are the second wave to arrive L Waves: Slowest moving seismic wave, but causes the most damage Richter Scale The Richter scale measures magnitude of an earthquake Magnitude is a measurement of the energy released by an earthquake Each whole number increase in magnitude is an increase of 31.7 times more energy Mercalli Scale A measurement of the intensity of an earthquake Parts of a Volcano Volcano: vent and the lava material that builds up around the vent Crater: Funnel shaped pit at the top of a volcanic pit Caldera: Large basin shaped depression at the top of a volcano. Usually due to a violent eruption Magma Volcanism: Any activity that includes the movement of magma toward or onto the surface Magma: Liquid rock Most magma is formed at a subduction boundary Lava: Magma that reaches the earth’s surface There Are Three Major Volcanic Zones Subduction Zones Mid-oceanic ridges Hot spots Subduction Zones Plate being subducted is turned into magma Some magma will erupt to form volcanoes EX. “The Pacific Ring of Fire” Mid Oceanic Ridge Greatest amount of magma surfaces here Diverging boundary Emerging lava forms new ocean floor EX. Mid-Atlantic Ridge Hot Spots Areas of volcanism within a plate Generally hot spots are shield volcanoes Ex. Hawaii There are Two Different Types of Lava Mafic lava is dark in color when cooled and usually produced from oceanic crust Felsic lava is lighter in color and usually produced from continental crust There are Three Different Types of Volcanoes Sheild Cone- Broad base and gently sloping sides Cinder Cone- Very steep slopes, not to tall Composite Cone- Develops into high volcanic mountains Composite Cone Mt. Rainer
