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Journey to the Surface of the Earth, part 2

Journey to the Surface of the Earth, part 2. Or, Earth from the Inside-Out. The Earth’s Interior. Yesterday we discussed these points: How we know about the interior of the Earth… How Earth’s interior took on the characteristics it has… The layers of the Earth as defined by composition

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Journey to the Surface of the Earth, part 2

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  1. Journey to the Surface of the Earth, part 2 Or, Earth from the Inside-Out

  2. The Earth’s Interior • Yesterday we discussed these points: • How we know about the interior of the Earth… • How Earth’s interior took on the characteristics it has… • The layers of the Earth as defined by composition • Today we will discuss: • The layers of the Earth as defined by behavior…

  3. Layers Due to Behavior • The Inner Core • Solid sphere at Earth’s center • High pressure maintains solidity even though temperatures are high enough to melt metal • Only 1200 km thick • Boundary between the inner and outer core is called the Lehmann Discontinuity

  4. Layers Due to Behavior • The Outer Core • Liquid, metallic core • High temperature creates convection currents • Vertical motion in a fluid like boiling water • Hot liquids are less dense (and so rise); cool liquids are more dense (and so sink)

  5. Layers Due to Behavior • Motion of the liquid metal produces a magnetic field – Earth’s “magnetosphere” • Without the magnetic field, Earth would be subjected to deadly radiation from the sun • Therefore, without the outer core, there would be NO LIFE on Earth

  6. Layers Due to Behavior • The magnetic field is due to the combined properties of the outer core • It is metallic AND it is liquid AND in motion • ALL THREE are required to produced the magnetic field • For example – Mercury has an iron core, but no magnetic field because it is solid! • Venus has a liquid iron core, but it has no magnetic field because there is very little motion within the liquid

  7. The Lower Mantle • The lower mantle is a thick (over 2200 km) layer of mostly solid rock • However, rock is not rigid but viscous-it can flow like a thick liquid (like cold honey) • Is responsible for heat transfer from the core outward

  8. The Asthenosphere • The asthenosphere is part of the upper mantle • It is consider a “plastic” zone – not complete molten, but not really rigid • Rocks in the asthenosphere are very close to their melting points and so deform easily • Convection in this region is thought to be the driving force of plate tectonics

  9. The Asthenosphere

  10. The Lithosphere • The lithosphere consists of the uppermost mantle and the entire crust • It is a solid, rigid layer that is broken into several “plates” • Lithospheric plates are large segments of the lithosphere that consist of oceanic and/or continental crust • Seven major and many minor plates (has changed throughout Earth’s history) • Plates are in constant motion

  11. The Lithosphere

  12. Motion in the Lithosphere • In the lower layers of the Earth (core, mantle), motion is dominated by convection • At the surface, this motion translates into lateral motion of the plates

  13. Motion in the Lithosphere • Two basic forces are thought control plate motion at the surface of the Earth: • Ridge-push • As new crust is generated at a mid-ocean ridge, the new crust (assisted by gravity) pushes the older crust aside • Slab-pull • When oceanic crust is forced under continental crust, the suction of the downward slab pulls the rest of the plate toward the trench

  14. Motion in the Lithosphere • Both forces act in tandem (together) along with convection to move the plates

  15. Summary • What are the five layers of the Earth as defined by behavior? • Why is the inner core solid? • What is the importance of the outer core? • What is the major role of the lower mantle? • How is the asthenosphere different from the lithosphere? • What is the importance of the asthenosphere?

  16. Summary • What are lithospheric plates? • What are the two forces that control plate motion? • What is the basic reason for plate motion?

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