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Earth's Geosphere
The document summarizes Earth's global structure and tectonic plate theory. It describes Earth's four main layers - crust, mantle, outer core, and inner core. The mantle is thick and dense, and convection currents there cause the movement of tectonic plates across Earth's surface. Plates meet at boundaries where earthquakes and volcanoes commonly occur as the plates converge, diverge, or slide past one another.
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Earth's Geosphere
- 1. The Geosphere Earth's GlobalStructure
- 2. Earth's composition • Crust –surface rock layer – relatively thin • Mantle – thick, dense silica layer where magma comes from • Outer Core – liquid iron/nickel • Inner Core – solid iron/nickel • liquid outer core spinning around solid inner core creates Earth's magnetic field
- 3. Earth's Layers Soil &Sediment: loose dirt and sand Crust: top surface layer of solid rock • 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/solid magma • magma (partially molten rock) • Lower Mantle • hotter & harder due to pressure Lithos phere Asthenos phere
- 4. Mantle = 1800miles Outer Core = 1300 milesInner Core = 800 miles Crust = 1 to 100 miles
- 5. Plate Tectonics • Slow-movingconvection 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.
- 6. Tectonic Plate Theory • Earth'scrust is divided into 15 major "plates" (slabs of crust) – continents are embedded in these sections of crust – some plates completely covered by ocean • Plates "float" above Earth's semi-solid 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 TectonicPlates 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. 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
- 9. • Earthquakes occuralong 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"
- 10. • Mountain building& trench formation • Volcanism • Earthquakes • Metamorphism & destruction of crust • Crust formation at ocean floor rifts What Occurs at Plate Boundaries?
- 11. 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
- 12. Volcano Types • Volcanoesform 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
Editor's Notes
- #4 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.
- #6 15 large plates, plus many more small plates.
- #7 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.
- #8 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.
- #11 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).