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Transcript
Bill Nye – Earth’s Crust The Cross-Section of Earth Review: The Cross-Section of Earth Earth is over 1200 km thick, and has four distinct layers. These layers are the crust, mantle (upper and lower), outer core, and inner core. Crust • Outer solid rock layer (granite on land, basalt in oceans) Mantle • Thickest layer, mostly solid except for upper mantle being able to flow like “thick toothpaste” Outer core • Composed of liquid iron and nickel Inner core • Mostly solid iron, at tremendous temperature and pressure Earth’s Layers Review: Earth’s Layers Tectonic plates make up the lithosphere, which floats on the asthenosphere. Lithosphere • The crust and upper portion of the upper mantle. Asthenosphere • The molten layer of the upper mantle. • Heat to keep asthenosphere molten comes from radioactive elements. • A convection current forms as hot, low density rock rises Convection Current (Mantle Convection) Review: Convection Current Continents, attached to the tectonic plates, float in the magma of the asthenosphere. As magma is heated in the asthenosphere, convection currents form. Rising magma can reach the surface at ridges (in the oceans) or rifts (on land). The magma cools when it reaches the surface, solidifies, and is pushed aside as new magma pushes from below. This is called ridge push. Pangaea Puzzle Evidence for Continental Drift Early maps of the world caused Wegener to continental drift theory propose the _______________________ because the continents looked as though they fit together like ______________. puzzle pieces might _____ The continental shelves actually fit together even better. This original supercontinent was Pangaea called ___________. Wegener also realized that other evidence also supported his theory. geologic features • There were matching __________________ and _______ rocks on different continents. Like pieces of a jigsaw puzzle, the continents fit together into one, large whole. mountain • It could help explain why ___________ ranges that begin on one continent, ________ end at the coastline, and then appear to continue on a continent across an ocean. http://geography.howstuffwo rks.com/terms-andassociations/pangaeasupercontinent.htm/printable fossils on different continents. • There were matching ________ • There was evidence of different __________ climates (e.g. glaciers) on warm continents. Glaciers vast masses of _____ ice _________: • Now found at the _______ poles and high in the mountains • Used to cover large areas of _______ land during __________ ice ages • When they __________ advance or _________, they _______ retreat mark the land, leaving behind large, Ushaped valleys, deeply scratched rocks, and various types of patterns of rock formations How Can Continents Move? Wegener’s evidence for continental drift didn’t explain how entire continents could change ___________. locations New scientific equipment allowed scientists to measure the _______, slow but ________, steady _______ drift of Earth’s _______________. tectonic plates It was noted that ______________ earthquakes and ___________ volcanoes appear in certain patterns, which happen to be along the edges of tectonic plates. Volcanoes are frequently boundaries found on _____________ between tectonic plates. Earthquakes and ___________ volcanoes are __________ dramatic events, where _____________ earthquake is a ________, sudden _________ release of built-up ________ energy at or under surface whereas volcanoes are __________ openings in Earth’s surface Earth’s _________ that spew out _______, gases chunks of ______, rock and melted rock when active. ocean floor revealed Mapping of the ____________ the __________________, MidMid-Atlantic Ridge a long mountain range running down the middle of the ________________. Atlantic Ocean ________ Rocks taken from the Mid Atlantic ridge were younger than other _________ ocean rocks. Sediments along the Ridge became _________ thicker further away from the ridge. magnetic field liquid iron Earth’s ________________ is produced by the motion of ____________ in the planet’s interior. Over time, the ____________ orientation of Earth’s reversed (“__________________”). magnetic field gets __________ magnetic reversal __________________ align with the Earth’s magnetic field IronIron-based metals in rocks _______ lines, similar to how a compass needle points north. Paleomagnetism shows that iron-based rocks along the ridges are _________ striped with reversing magnetic fields. Sea Floor Spreading: An Explanation magma rose to form new rock at certain Hess suggested that _________ places. melted rock • Magma (_____________), rises and falls like warm and cold liquids. The ___________________ convection current of magma formed a _________________ spreading ridge where it broke through Earth’s ______ crust (“new crust” conveyer belt). __________________ Magnetic striping of basalt rock shows long stripes of ______ new rock ______________ moving away from ocean ridges, and also reveals the direction of Earth’s magnetic field at that time. hot spots are anywhere __________ magma rises to Earth’s Geologic ___________ surface. Wilson then unified the ideas of Wegener and Hess into the plate tectonic theory. He explained continental drift occurs because of areas like these ridges, that _______ push along ________________ tectonic plates floating on Earth’s surface. Figure 21 - Hawaiian hot spot volcanism, displaying the tell-tale track of volcanoes which grow older away from current active volcanoes. These volcano tracks indicate that the lithospheric plate is moving over a stationary mantle plume. Plate Interactions A plate boundary is where contact two plates are in _________. The way the plates interact is based on the type of plate, and the direction the plates are moving relative to each other. Tectonic plate boundaries, and their relative movement to each other. Divergent plate boundaries 1. ___________ spreading apart • Plates are ________________ ridges and • E.g. Ocean _______ rifts continental ______ MidMid-Atlantic Ridge is the • The ___________________ mountain range on Earth longest __________ Divergent Plate Boundaries (Mechanism) Divergent Plate Boundaries (Examples) Tectonic plates _______________ are all moving at the same time. There are 12 large tectonic plates, and many smaller ones. Where continental and oceanic plates meet, subduction occurs. ____________ dense oceanic plate subducts under the ________ lighter • More ________ continental plate. slab pull • By “__________”, the rest of the plate follows. volcanoes are found in subduction earthquakes and ___________ • Large _____________ zones. Convergent Plate boundaries 2. _____________ meet and ________ collide • Plates _______ 3 Types: OceanicOceanic-Continental plate convergence i) ___________________ The oceanic plate __________ subducts under the trench continental plate, forming a ________. Cone-shaped ___________ volcanoes can form from magma seeping to the surface. • This is how the _____________ volcanic belt of the Pacific Northwest has formed. Coast Mountain Mountain ranges like the ________________ range also form from the collision. _______ Earthquakes can occur when subduction, ridge push and slab pull stall. Oceanic-Continental Convergent Plate Boundaries (Mechanism) Oceanic-Continental Convergent Plate Boundaries (Examples) Coast Mountains of British Columbia OceanicOceanic-Oceanic plate convergence ii) _________________ cooler _____________ more dense The ________, plate (older crust) will subduct under the other. Convergence may produce a volcanic island arc such __________________, as those found in Japan, Indonesia and Alaska’s Aleutian islands _________________. Oceanic-Oceanic Convergent Plate Boundaries (Mechanism) Oceanic-Oceanic Convergent Plate Boundaries (Example) Aleutian Island of Alaska in U.S. ContinentalContinental-Continental plate convergence iii) _______________________ Since both are continental densities are plates, __________ equal ________. fold As they collide, edges ______ and crumple, forming mountain ranges. Himalayas are the world’s youngest (and tallest) E.g. The ____________ mountain range. • They formed as _______ Asia and Africa plates collided 40 ________ million years ago. taller • They are still growing _______ today. Continental-Continental Convergent Plate Boundaries (Mechanism) Continental-Continental Convergent Plate Boundaries (Examples) Himalayas 3. ___________ Transform plate boundaries move past each other horizontally • Plates ___________ ocean ridges • Usually are found near ______________ slides past rock in these boundaries, • Since rock ________ NO earthquakes and _________ faults are very common, but _____ _____________ mountains or volcanoes will be formed Transform Plate Boundaries (Mechanism and Example) Overall Summary Earthquake Video Earthquakes Earthquakes often form from the friction between moving _________ tectonic plates. This accounts for 95% of all earthquakes. Pakistan Earthquakes are very difficult to predict _________. Scientists understand why they happen, but it is very timing difficult to predict their ________, exact _________ location and _________. strength • Their build-up happens underground over very _____________, long periods of time. • What we do understand has structures helped prepare ___________ to survive them. San Francisco Earthquakes (Mechanism) The ________ focus of the earthquake is the location inside Earth where an starts This is where _________ energy and __________ pressure get earthquake ________. released __________. epicenter is the point on The ___________ directly above the the surface ______________ focus. Waves of Energy travel outwards from the focus of an earthquake. Example Juan de Fuca convergent plate boundary west of Vancouver The ______________ earthquakes Large earthquakes hit this region Island has many _____________. every 200 - 800 years. Earthquakes occur at various _________, depths depending on the type of tectonic plate interaction plates involved. Earthquakes at the _________ surface tend to cause _______________. more damage energy of an earthquake is Seismic waves form when the ________ _______________ released. Seismology is the study of these waves. ____________ source and _________ • These waves reveal the ________ strength of an earthquake. composition and __________ distances • They also help us learn about the ____________ of the Earth’s interior. Seismic waves behave ___________ differently in different Earth layers. • The movement of waves through Earth’s interior is affected by the density and depth of the different layers composition (________) • Knowing this, scientists can learn much about both earthquakes and the ________ interior of Earth. Note: S-waves disappear at the bottom of the mantle because they cannot liquid outer core. travel through the _______ ______________ Seismometers are used to measure seismic wave energy. • Records the ___________ vibrations from earthquakes • Early seismometers just ground measured if the ________ shook or not. • Some seismometers measure horizontal movement, others vertical movement. seismogram is produced, A _____________ showing when an earthquake started, how long it lasted, and magnitude the ____________. ___ 1 in magnitude = ______ 10X stronger 100X more powerful than a 4. E.g. A magnitude 6 earthquake is _______ Since seismic waves travel at different ________, speeds a distance-time graph, revealing the focus. Bill Nye: Volcanoes Volcanoes The movement of tectonic plates causes volcano formation Composite volcanoes - this is the stereotypical volcano, 1. ___________ smoke and ______ ash everywhere, found erupting and belching _________ plate boundaries along ________________. Layers of ash and thick ______ lava (magma outside Earth) form cone a tall ______. magma reaches the surface, it _______, cools __________ hardens As _________ gases below. and traps _______ Pressure builds, eventually there is an ___________. eruption __________ Mount St. Helens, Washington Shield volcanoes - these are NOT found at plate boundaries, 2. ________ but instead form over hot spots (a weak spot in the normal lithosphere). hot spot and forms a Thin magma/lava flows out from a __________ _____ low , wide _______. cone The _________________ Hawaiian Islands are an example of a chain of shield volcanoes. Yellowstone National Park cracks in the 3. ______________ Rift eruptions - these occur along long ________ lithosphere _____________ massive amounts of These are NOT explosive, but release _________ lava ______. Ridges are due to rift eruptions under the ocean. The Krafla volcano, Northern Iceland