1. - To Accompany Discovery Techbook Mrs. Baker/cjcb

3. Compositional layers of the Earth  Inner core  Outer core  Mantle  Crust ◦ Compositional layers have different chemistries, e.g. aluminosilicate (Al, Si, O); iron- nickel alloy (Fe, Ni)

4. Structural layers of the Earth  Inner core  Outer core  Mantle ◦ Mesosphere ◦ Asthenosphere  Lithosphere ◦ Structural layers have different mechanical properties, e.g. liquid, solid, brittle, etc.

5.  Made up of the earth’s crust and upper portion of the mantle (which behaves more like the crust than the mantle below)  A structural layer of the Earth ◦ Rocky and brittle ◦ Cracks under pressure  Crust is made of continental crust and oceanic crust ◦ Continental crust is older ◦ New oceanic crust is constantly made at mid-ocean ridges and is recycled at subduction boundaries

6.  Continental and Oceanic Crust differ by: ◦ Composition ◦ Density ◦ Thickness ◦ Average age

7.  66% of the earth’s mass is here.  Has two structural layers—asthenosphere and mesosphere  Asthenosphere is soft and putty-like. It flows. The crust floats on this portion of the mantle.  At the mesosphere, the pressure is too great for the rock to “flow”.

8.  Almost all of the remaining 33% of earth’s mass is the core….almost entirely iron and nickel.  Outer core is liquid….how do we know this?  Inner core is solid. Why?  Watch: “Determining the Structure of the Earth” video on the Engage! page

10.  Was just an idea….now it’s a sensation!  sid the sloth continental drift video - Bing Videos sid the sloth continental drift video - Bing Videos

11.  The idea that Earth’s surface is moving is not new.  In the early 1500’s, explorers using maps noticed how well the west coast of Africa and the east coast of South America fit together.

12.  1912 – Alfred Wegener proposed continental drift. ◦ Used additional information such as the location of similar fossils and similar rock formations on opposite sides of the ocean to support his hypothesis. ◦ Thought that the continents pushed through the rocks of the ocean floor  Continental drift – a hypothesis that Earth’s continents move on Earth’s surface.

13.  Wegener proposed that the continents came together to form a single large land mass called Pangaea about 300 million years ago.  How well can you do this? ◦ “Earth’s a Puzzle” exercise

14.  Wegener’s theory of Continental Drift was not well-received at the time ◦ Wegener’s mechanism for continental drift wasn’t accepted. People just couldn’t believe that huge continents moved! ◦ Scientists of the time would “explain away” Wegener’s ideas and evidence.

16.  In the 1950s and 1960s, discoveries about earthquakes, magnetism, and the age of rocks on the ocean floor helped support some of Wegener’s ideas.  Scientists in the ’60s also proposed that the sea-floor is spreading: new ocean material is formed at ridges and then moves away towards subduction zones ◦ The sea-floor is a conveyer belt  Explains why earthquakes and volcanoes are likely to occur in particular locations and how new crust forms along the ocean floor.

17. So what latest and greatest evidence was used to develop “plate tectonic theory?”

18.  Earthquakes do not occur randomly.  They occur primarily in concentrated belts. http://www.pbs.org/wgbh/nova/teachers/activities/2515_vesuvius.html

19. Plate BoundariesEarthquake Activity

21. You find mainly BLUE triangles along ocean ridges but RED, GREEN, and BLUE at other plate boundaries.

22. The different colors are for different types of volcanoes. One important fact is that the composition of magma is NOT the same for all volcanoes: BLUE triangles have less viscous magma – think oozing like the Hawaiian Islands or Iceland RED and GREEN triangles have more viscous lava, and so are more violent – think Mount St. Helens in Washington State

23.  The earthquake and volcano belts mark the locations of plate boundaries. ◦ Where two plates are pushing toward, pulling away, or sliding past each other. ◦ Strain builds up along plate boundaries, allowing fractures to form  earthquakes. ◦ Areas of high heat flow  volcanoes  Different depths of earthquakes and different types of volcanos are seen at different types of plate boundaries

25. The islands get older the farther you move from the Big island of Hawaii (which is erupting now!) The trail of islands is thought to show plate movement.

26. * evidence of sea-floor spreading!

27. The ocean crust is disappearing

29.  Some igneous rocks contain magnetic materials.  These magnetic minerals provide a record of the direction of Earth’s magnetic field at the time when the molten rock cooled.

30.  Geologists found that at certain times, rocks reversed polarity.  This led to the discovery that at certain times, Earth’s current magnetic north became magnetic south.  Many magnetic reversals have occurred.

31.  Mid-ocean ridge – long chain of volcanic mountains on the ocean floor with a deep central valley.  Magnetic reversals are recorded in bands of rock on either side of the ridge.  The center of the ridge (newest rocks) always shows the current orientation of the north and south poles.

32.  Ridges represent boundaries where lithospheric plates are moving apart.  Newer rocks along a mid-ocean ridge are formed by hot, molten rock rising between the spreading plates.  As new rocks form, the older rocks move further from the ridge.

33. Layers of the Earth – Mr. Lee Lyric Video: http://www.bing.com/videos/search?q=Layers+of+the+Earth+Song &Form=VQFRVP#view=detail&mid=9F66B8A706BFB99772729F66B8 A706BFB9977272

34.  Boundary between two lithospheric plates that are moving apart.  Sometimes called spreading centers.

35.  Rift valleys – deep valleys at the center of a mid-ocean ridge.  Rift – crack in the valley  Sea-floor spreading – molten rock forces its way upward through rifts.

36.  Boundary between two plates that are moving toward each other (converging).  Two main types: ◦ Subduction Boundaries ◦ Collision Boundaries

37.  Subduction Boundary – when an oceanic plate plunges beneath another plate. ◦ Deep-sea trench – long deep trench that forms at a subduction boundary. ◦ Accompanied by the formation of a chain of volcanic islands called a volcanic island arc. ◦ Deep earthquakes occur at subduction zones

38.  Collision Boundary – the boundary that forms when two continents collide and are welded into a single, larger continent. ◦ Causes the crust at the boundary to be pushed upward into a mountain range. ◦ Shallow to medium depth earthquakes are common

39.  A boundary between two plates that are sliding past each other.  Fracture zones that offset the segments of a mid-ocean ridge.  Movement along these boundaries is not uniform.  Location of abundant shallow earthquakes (San Andreas Fault)

40.  Seafloor spreading centers  “Symmetry” of landforms along either sides of ocean ridges  Fossil records matching up in distance places  We can now measure plate movement using GPS. Plates each move at different rates ◦ Average rate is a few centimeters per year

41.  Mantle convection  Ridge push  Slab pull

42.  The process by which heat from Earth’s inner and outer cores is transferred through the mantle.  The mantle may be moving the plates along with it as it convects.

43.  The process by which the cooling, subsiding rock exerts a force on spreading lithospheric plates that could help drive their movement.  Could also be called gravitational sliding.

44.  The process by which the sinking edge of the plate exerts a force on the rest of the plate.

45.  The tectonic plates have moved extensively in the past:  http://education.nationalgeographic.com/ma ps/earths-tectonic-plates/ http://education.nationalgeographic.com/ma ps/earths-tectonic-plates/  And they are still slowly moving…