Plate Tectonics
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Plate tectonics involves the slow movement of sections of Earth's crust called tectonic plates. Plates move due to convection currents in the underlying mantle. Where plates meet, they can cause earthquakes, volcanoes, and mountains as the plates push together, slide past each other, or move apart. The movement of plates over time has resulted in continents joining together in a supercontinent called Pangea and breaking apart again.
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Plate Tectonics
- 1. Science is Organized Knowledge Earth & Space ScienceEarth & Space Science The Geosphere III Plate Tectonics
- 2. 1. What naturally occurring, organic substances with crystalline structure combine to form rocks? • minerals 1. Name the three major rock types and briefly explain how they form. • Igneous – cooled magma or lava • Sedimentary – compressed layers of sand/sediment, cemented together via minerals • Metamorphic – rocks changed by heat and pressure 3. True or False? Extrusive igneous formations occur when molten rock in Earth’s mantle rises and cools within the crust (also called an igneous extrusion). • False (extrusive = cooled lava, intrusive = cooled magma below the surface) 4. Which type of rock is most easily weathered? • Sedimentary rock (is softer than igneous or metamorphic) 4. Name the four layers of the earth and give one fact about each. • Inner Core – Outer Core • Mantle – Crust Bonus: Write a conclusion for last week’s lab, based on your observation chart. Was your hypothesis supported by what happened in the experiment? Week 4 Review Quiz In your lab notebook, please answer as best you can:
- 3. Earth's Layers Lithosphere TECTONIC PLATES Asthenospher e Crust: top layer of bedrock topped by soil • Thicker Continental crust, ~30km (19mi) • Thinner Oceanic crust, ~5 km (2 mi) Mantle: thick, dense silica, (2,900 km/1800mi) • Upper Mantle • topmost layer of cooler, more solid magma attached to crust • deeper magma (softer molten rock) •Transition zone • trapped “water” crystals (hydroxide ions) – LOTS! •Lower Mantle • hotter, denser, & more solid due to increased pressure
- 4. Plate Tectonics • Slow-moving convection currents in the mantle cause sections of Earth's crust to move above • Fault lines are the boundaries where plate edges meet. • Earth's crust is broken up into sections called plates that drift slowly above the syrupy mantle.
- 5. Observat i on: - Convect i on i s t he t r ansf er of heat due t o movement wi t hi n a f l ui d ( ai r / wat er / magma) . - Heat measur es t he speed of mol ecul es. - Densi t y measur es how t i ght l y packed t oget her t he mol ecul es of a subst ance ar e. - Fast er movi ng mol ecul es ar e l ess dense ( f art her apar t ) t han sl ower ( col der ) mol ecul es. - Hot ai r & wat er ar e l ess dense t han cool er f l ui ds. - Obj ect s t hat ar e l ess dense t han wat er wi l l f l oat . QUESTION: How does heat af f ect movement wi t hi n a f l ui d? Hypot hesi s: If wat er i s heat ed i n one ar ea of a t ub and mar ked wi t h r ed f ood col or i ng, t hen i t wi l l … , because … If an i ce cube col or ed wi t h bl ue f ood col or i ng • Observation: • What do you know? • What do you want to fix/solve/learn? • Hypothesis: • What do you think will happen & why? • Experiment: • What happened? • Record your data/observations. • Conclusion: • Does the data support your hypothesis? USE COMPLETE SENTENCES t o a ns we r t he s e Concl usi on Quest i ons: 1. I n whi ch di r ect i on di d t he war mer f l ui ds move? •Do e s t hi s s up p o r t y o ur hy p o t he s i s ? 2. I n whi ch di r ect i on di d t he cool er f l ui ds move? •Do e s t hi s s up p o r t y o ur hy p o t he s i s ? 3. Di d t he heat ed/ cool ed f l ui d move si deways at al l ? •Wha t d o y o u t hi nk c a us e d t hi s ? I f t her e’ s t i me: 4. I f one beaker cont ai ned 100 mL of col d wat er and anot her had 100 mL of hot wat er , whi ch beaker woul d cont ai n mor e mol ecul es? Expl ai n why. 5. Whi ch wat er ( hot or col d) woul d have t he gr eat er mass? Whi ch woul d have t he hi gher densi t y? 6. Ai r , wat er , and magma ar e f l ui ds. What wi l l happen t o an ar ea wi t hi n a f l ui d t hat becomes war mer t han t he Convection Currents Experiment 4
- 6. Tectonic Plate Theory • Earth's crust is divided into 15 major "plates" (slabs of crust and outer upper mantle) – continents are embedded in these sections of lithosphere – some plates are completely covered by ocean • Plates "float" on Earth's semi- solid upper mantle – move an average 2.5 cm/yr – movement tracked by GPS • Evidence supplied by: – worldwide seismology • earthquakes • volcanic eruptions – magnetic stratigraphy – deep sea exploration – satellite imagery Seismic Activity
- 7. Why Do Tectonic Plates Move? • Convection currents in the mantle below move plates – hot = less dense (rises up) – cool = denser atomic structure (sinks down) • Plates move at a rate of about 1 - 6 cm per year
- 8. Earthquakes: Rapid movements of earth's crust along fault lines as pressure is released (used to identify tectonic plate boundaries) Volcanoes: Release of magma along plate boundaries Tectonic Plates Tsunamis: tidal waves caused by earthquakes on the ocean floor
- 9. Pangea • a theoretical single super-continent • based on similar rock types and fossils that date to the same age found on separate modern-day continents
- 10. Tectonic Plate Boundaries • Convergent: plates move toward one another • crust destroyed along subduction zones • Divergent: plates move away from each other • crust is formed • Transform: plates slide alongside each other
- 11. • Earthquakes occur along fault lines as pressure from moving plates is rapidly released • Magnitude describes the size of an earthquake • Volcanic eruptions are triggered, trenches are formed, and ridges of newly released magma also build up along plate boundaries The Pacific Plate's "Ring of Fire"
- 12. • Mountain building & trench formation • Volcanism • Earthquakes • Metamorphism & destruction of crust • Crust formation at ocean floor rifts What Occurs at Plate Boundaries?
- 13. Volcanic Eruptions • Lava – lava flows out of vents (openings) in Earth's crust onto the surface before cooling, hardening, and becoming solid rock • Tephra – tiny pieces of glass from rapidly cooled and solidified lava form ash – can be blown high into the atmosphere • Pyroclastic flow – dense mixtures of hot, dry rock fragments and gases that move at high speeds • Lahar – a hot or cold mixture of water and rock fragments that flows like a river and causes rapid erosion and sedimentation
- 14. Volcano Types • Volcanoes form differently depending on viscosity (thickness) of lava expelled: • Shield Volcano - liquid lava develops long gentle slopes • Cinder Cone - explosive, runny lava forms a cone • Composite or Strato-volcano - thicker lava & pyroclastic flows form steep-sloped peaks • Lava Dome - very thick lava piles up into big mound around a central vent • Caldera - peak collapses after exploding Flood Basalt
- 16. Uplift and Erosion Uplift simply moves the strata, allowing for erosion to expose formerly buried layers. Without uplift (& volcanic eruptions), the earth's surface would eventually become completely smooth and flat and entirely covered with water. The movement of Earth’s tectonic plates can cause a lifting up of previously buried rock layers.
Editor's Notes
- There are very thin layers of the lithosphere (only 5 km thick), but they only exist beneath the deepest parts of the ocean. Now you know why we have not observed any section of the earth other than the lithosphere. The deepest that any drill has ever penetrated the lithosphere is 15 kilometers. Since drilling does not take place in the deep ocean, you can see that drilling has not come close to penetrating through the lithosphere. Mantle: like warm plastic, flows about 10cm per year.
- 15 large plates, plus many more small plates.
- Observation – what do you know about heat & density? - Convection is the transfer of due to movement within a fluid (air/water/magma). - Heat measures the of molecules. - measures how tightly packed together the molecules of a substance are. D = mass/Volume - Faster moving molecules are less dense ( apart) than slower (colder) molecules. - Hot air & water are less than cooler fluids. - Objects that are less dense than water will . QUESTION: How does heat affect movement within a fluid? Hypothesis – what do you think will happen and why? If water is heated in one area of a tub and marked with red food coloring, then it will , because . If an ice cube colored with blue food coloring is placed in a tub of room-temperature water, then it will , because . Experiment Materials: clear plastic tub, pipette, Styrofoam Cups, food coloring, water (hot and cold), colored ice cube, plastic spoon Procedures: Fill a plastic tub half full of room-temperature water. Carefully place two nested Styrofoam cups under each corner of the tub and let the water become still. Use a pipette to place 3 spots of red food coloring on the bottom of the tub, one at each & one in the center. Fill one empty Styrofoam cup with hot tap water and carefully position it beneath the center dye spot. Viewing the box from the side, record what happens over the next 5 minutes. Carefully empty the tub water in a sink (or use new tub). Repeat steps 1 – 3. Then fill two cups with hot water and position them beneath the two outside spots. Observe what happens over the next 10 minutes and record your findings. With a new (or rinsed out) tub, repeat steps 1 – 3 again, but only place two spots of dye on the bottom (one center and one near the end). Fill two cups with hot water and set beneath each spot. Use a plastic spoon to gently place a colored ice cube into the water at the opposite end of the tub from your dye spots. Use the spoon to stop the cube from moving. Record your observations as the ice cube melts.
- The Worldwide Standardized Seismic Network created a global system of seismographs all using common timekeeping standards and sending data to common repositories. This system allowed radical improvements in accuracy of earthquake locations. Instead of showing a diffuse smear of seismicity along the mid-ocean ridges, the system showed that earthquakes were confined to extremely narrow zones along the crest of the ridges. Basically, the new maps showed that the earth consisted of large blocks or plates of crust with little earthquake activity, bounded by narrow zones of high activity. There is some activity within the plates. If it looks like the U.S. and Western Europe are particularly hard hit, that reflects the concentration of sensitive instruments capable of detecting tiny earthquakes in those regions.
- Theories: Slab pull - The sinking of the cooled dense oceanic plates pulls on the rest of the plate Ridge rises - The material deposited on the top of the ridge slides downs from the rise pushing on the plate Convection - Movement within the mantle could be part of the driving force behind the motion of the plates No single idea explains everything but we can identify several forces that contribute to the movement of the plates.
- Deepest quakes occur along subduction zones
- The Mariana Trench or Marianas Trench is the deepest part of the world's oceans. It is located in the western Pacific Ocean, to the east of the Mariana Islands. The trench is about 2,550 kilometres (1,580 mi) long but has an average width of only 69 kilometres (43 mi). It reaches a maximum-known depth of 10.911 km (10,911 ± 40 m) or 6.831 mi (36,069 ± 131 ft) at the Challenger Deep, a small slot-shaped valley in its floor, at its southern end,[2] although some unrepeated measurements place the deepest portion at 11.03 kilometres (6.85 mi).