1 / 24

Bellwork What causes the continents to drift?

Fact: The tallest mountain on the planet is not Mt. Everest, which is only 29 028 ft.  The tallest mountain in the world is actually Mauna Kea, in Hawaii, which is closer to 31 000 ft. You just can't see the two-thirds of the mountain that is under water.

trevet
Download Presentation

Bellwork What causes the continents to drift?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Fact: The tallest mountain on the planet is not Mt. Everest, which is only 29 028 ft.  The tallest mountain in the world is actually Mauna Kea, in Hawaii, which is closer to 31 000 ft. You just can't see the two-thirds of the mountain that is under water. Bellwork What causes the continents to drift? http://www.youtube.com/watch?v=7Y3mfAGVn1c&feature=related

  2. Sea-Floor Spreading

  3. Earth: Compositional Layers

  4. Composition Physical Characteristics crust Brittle, solid Similar to mantle but with lighter metals lithosphere Solid, but behaves plastically asthenosphere mantle Mostly silica, magnesium, iron, with some other stuff Solid but flows slowly over long periods of time mesosphere Liquid outer core Mainly iron and nickel inner core core Solid Note: Lithosphere contains both crust and uppermost (brittle) layer of mantle

  5. Effects of Density: A block of continental lithosphere (containing continental crust plus uppermost ) stands higher than a block of oceanic lithosphere (containing oceanic crust) of the same dimensions Continental crust: 2.7 g/cm3 Oceanic crust: 3.0 g/cm3 Lithospheric mantle ~ 3.3 g/cm3 Lithospheric mantle ~ 3.3 g/cm3 Asthenosphere (near-liquid part of mantle) Oceanic lithosphere floats low on asthenosphere (forms basins) Continental lithosphere floats high on asthenosphere (forms continents)

  6. Effect of Lithospheric Thickness: For a buoyant material, a thick block stands higher than a thin block Example: top surface of thick block of wood stands higher above water level than that of thin block of wood. However, the proportion of material standing above and below water mark is the same for all blocks. So, low density of continents combined with great crustal thickness make continents stand higher than ocean floors

  7. Focus your attention to interaction of brittle lithosphere and near-liquid asthenosphere

  8. Volcanoes Location, Location, Location Earthquakes

  9. More recent evidence of seafloor spreading 1. Symmetry of magnetic stripes (defined by polarity of magnetic minerals in basaltic rock of seafloor) Symmetrical pattern of normal and reverse polarities on either side of a divergent boundary can only be explained if new crust was being formed and repeatedly split apart as magnetic field reversed

  10. More recent evidence of seafloor spreading 2. Linear arrangement and relative heights of hotspot volcanoes (volcanoes produced by movement of plate over stationary magma plume from mantle) Note: heights of hotspot volcanoes are decreased with increasing distance from point of active volcanism (due to cooling and sinking of lithospheric material)

  11. But how does seafloor spreading (divergence) start ? Hot plume in mantle upwarps lithosphere of continent Cracks develop (generally in a triple junction), forming rift valleys Zones where adjacent fractures connect allow further spreading to produce an ocean Failed arm ceases to spread (Bay of Fundy basin represents a “failed arm” of the Atlantic Ocean basin)

  12. Mid-Ocean Ridge • Longest chain of mountains in the world • Mostly under water • Iceland is where the ridge rises above the water • Sonar- device that scientists use to map the ocean floor

  13. Red Sea-Gulf of Aden: An ocean basin in the making East African Rift will probably stop spreading and become a “failed arm” Future ocean basin

  14. Topographic map of the ocean floor

  15. Sea Floor Spreading Molten material rises from the mantle and erupts Molten material spreads out, pushing older rock to both sides of the ridge New crust is being created

  16. Evidence for Sea-Floor Spreading 1) Molten Material 2) Magnetic Stripes 3) Drilling Samples

  17. Molten Material • Pillow lava at the Mid-Ocean ridge - pillow lava are rocks that form when molten material cools and hardens quickly in water

  18. Magnetic Stripes • rock on the ocean floor is in a pattern of magnetic stripes • Stripes show when the magnetic poles on Earth have reversed • Stripes match on each side of the ridge

  19. Drilling Samples drilled samples of ocean floor and dated the rocks Found rocks near the ridge were youngest and rocks farthest from ridge were oldest

  20. Subduction Process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary Deep-Ocean Trench- a deep valley along the ocean floor Destroys crust Pacific- shrinking- destroy more than create Atlantic- expanding- create more than destroy

  21. http://www.youtube.com/watch?v=ryrXAGY1dmE&NR=1&feature=endscreenhttp://www.youtube.com/watch?v=ryrXAGY1dmE&NR=1&feature=endscreen http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=related

  22. Implications of Plate Tectonics While ocean basins are created and destroyed continents are too light to be subducted, so simply break apart and collide Continental Drift: 750 million years ago to present

  23. The End

More Related