Plate tectonics ch 28.2

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Plate tectonics ch 28.2

  1. 1. Mrs. Neistadt Physical Science
  2. 2.  The theory of plate tectonics explains the movement of continents and other geological events like earthquakes and volcanoes.  The term tectonics means construction or building. *The theory of plate tectonics, stated in 1965, refers to the movement of giant pieces of solid rock on Earth’s surface called tectonic plates.
  3. 3.  In 1915, Alfred Wegener (1880-1930), a German meteorologist, wrote a book titled The Origin of Continents and Oceans. *Alfred Wegener gathered evidence that supported his idea that all the continents had been connected. *This was the Theory of Continental Drift. 1915
  4. 4.  In the early 1960s, Henry Hess (1906-69), a geologist and former commander of a Navy ship equipped with an echo sounder, used the profile of the sea floor to propose that it was spreading at the mid- ocean ridges.  An echo sounder is used to make a profile of the sea floor.
  5. 5. *Harry Hess *An American geologist who studied mid-ocean ridges. *He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.
  6. 6.  The theory of plate tectonics explains the movement of continents and other geological events like earthquakes and volcanoes. The term tectonics means construction or building. *The theory of plate tectonics, stated in 1965, refers to the movement of giant pieces of solid rock on Earth’s surface called tectonic plates.
  7. 7.  Around the same time, Robert Dietz (1914-95), a scientist with similar ideas, coined the term sea-floor spreading. *Sea-floor spreading describes the sea floor on either side of a mid-ocean ridge as moving away from the ridge and creating a rise or valley.
  8. 8.  *Hot fluid from the mantle (called magma) enters the rise or valley and cools, creating new sea floor (also called oceanic crust).
  9. 9.  In the 1950s and 1960s, scientists discovered that the rocks of the sea floor have a very interesting magnetic pattern. *Over geologic time, the magnetic polarity of Earth has switched. *Scientists believe the poles switch because of a magnetic interaction between the planet’s inner and outer core.
  10. 10.  Stripes of rock with a north-south orientation (normal) alternate with stripes of rock with a south-north orientation (reversed). The blue and white stripes you see in the figure are an interpretation of a magnetic profile.
  11. 11.  The Earth is like a bar magnet, It has a North and South pole. SketchBar magnet. Iron filingsline up with magneticfield. Concept
  12. 12.  The Geographic North and Magnetic North are not in the same place. The asterisk marks Magnetic North or True North.
  13. 13.  *The Earth’s magnetic poles switch direction.  The south pole becomes the north pole, and the north pole becomes the south pole *This switch in direction is known as Magnetic Reversal. Such reversals are caused by changes in Earth’s magnetic field. *Earth’s Geographic Pole never changes place.
  14. 14.  *Each Magnetic Reversal is recorded in the sea-floor rock. As the molten material rises and cools, iron particles line up with Earth’s magnetic field. When the material hardens, these particles stay in place like compass needles that are stuck in position forever.
  15. 15.  *The records of magnetic reversals line up like stripes in a rock Evidence of plate movement is found by finding the age of the rock. The youngest rock shows the last magnetic reversal occurred about 760,000 years ago. The oldest reversal we have found happened 150 million years ago.
  16. 16. Can you identify which of the plates are only made of oceanic crust?
  17. 17.  Use usgs.gov to find earthquakes in real-time to map the tectonic plates.
  18. 18.  There are three main kinds of plate boundaries:  divergent  convergent  transform
  19. 19.  The tectonic plates that cover Earth’s surface are pieces of the lithosphere that fit together and float on the asthenosphere (a part of the mantle). There are a number of large tectonic plates on Earth’s surface, and smaller plates are being identified all the time.
  20. 20.  Diverging plates move apart and new crust forms.
  21. 21.  Divergent boundaries are sites of earthquakes and volcanic activity. Mid-ocean ridges and associated sea-floor spreading occur at divergent plate boundaries. In effect, a mid-ocean ridge is like a very long volcano.
  22. 22.  Convergent plate boundaries occur where two plates approach each other. One result of two plates converging is subduction. A deep oceanic trench marks the boundary between a subducting and an overriding plate at a convergent boundary.
  23. 23.  The movement of tectonic plates is related to the distribution of heat by convection currents in the mantle.
  24. 24. Key Question:  What will Earth look like in 50 millions years?*Read text section 28.2 BEFORE Investigation 28.2

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