Plate Tectonics

1. Plate Tectonics 8th grade science

2. Vocabulary • Crust - layer of rock that forms Earth’s outer layer, composed of basalt and granite • Mantle – below the crust, layer of hot rock, composed of 2 parts • Lithosphere – rigid layer of upper part of mantle • Asthenosphere – lower soft layer of mantle • Core – center of earth, composed of 2 parts • Continental drift – idea of continents moving slowly over Earth’s surface

3. Continental Drift • First hypothesised by Alfred Wegener – 1910 • His idea that all continents were joined mya • Tens of millions ago landmass began to break apart – called • continental drift • Looked at evidence from: • landforms- mountain ranges, other • features line up on other continents • fossils-same type of fossils found on continents • oceans apart • climate- fossils of tropical plants found on • continents that are now in polar climates Modified from USGS

4. Alfred Wegener Born Nov. 1, 1880 Ph.D astronomy- University of Berlin- 1904 Made contributions in meteorology Went on expedition to Greenland – studied polar air circulation During research reads paper linking fossils of identical plants, animals, found on opposite sides of Atlantic Began looking for other cases where similar organisms separated by oceans

5. Alfred Wegener cont. Noticed close fit between coast of S. Africa and S. America Needed large amt. of supporting evidence Published 1915 – The Origin of Continents and Oceans Claimed continents were a single mass 300mya Called it Pangea Hypothesized that over tens of millions of years Pangea broke apart – known as continental drift Looked at landforms (coastal mts. of S. Africa & S. America) Originally was not believed Died while on expedition to Greenland – 1930 http://www.ucmp.berkeley.edu/geology/tectonics.html

6. Earth’s Interior • Study surface directly and use indirect evidence to study interior (seismic waves) • As you descend towards middle temperature and pressure increase • Have 3 basic layers - crust mantle core http://volcano.und.edu/vwdocs/vwlessons/lessons/Earths_layers/Earths_layers2.html

7. Crust • 70% covered water • 30% seven continental continents • Under oceans, dirt, & plants is layer of rock • Layer formed from cooled lava 4.5bya • About 250mya land was connected together -Pangea • Oceanic crust under ocean, mostly dark, dense rock • Continents made of granite, is less dense, has large crystals, light color

8. Mantle Below crust is mantle – layer of hot rock Upper part of mantle is rigid, called lithosphere, is about 100km Below that is asthenosphere – is like plastic, able to flow smoothly, is about 350km Mantle extends to core, is nearly 3000km thick

9. Core Core contains 2 parts – inner and outer Made of iron and nickel Outer layer is molten metal, is like thick liquid even though is under extreme pressure Inner layer acts like solid due to pressure, is under extreme heat Both layers compose 15% of earth’s volume but only 1/3 of mass Is just smaller than moon

10. Magnetic Field Currents in outer core cause inner core to spin Inner core spins faster than rest of planet Movement causes planet to have large magnetic field Planet acts like large bar magnet Magnetic field causes compass to align to N pole http://www.adlerplanetarium.org/cyberspace/planets/earth/#magnetic_field

11. Convection Currents in Mantle Heat from core and from mantle cause convection currents in mantle Heated magma rises and spreads out and pushes cooler magma out of the way Cooler material sinks to bottom to be heated again, which causes it to rise thereby creating a convection current Currents have been moving inside earth for more than 4 billion years

12. Lab - Continental Drift Question: How do the continental plates move? Hypothesis: Material: hot plate scissors baking pan water tongs map sheets of foam and cork Procedure: 1. Using the scissors cut out 3 or 4 plates from the map. Then copy them onto either a square of cork or colored foam. Cut them out. 2. Turn the hot plate on high. Place a baking pan filled with water on the ‘ hot plate. 3. Gently place the cut out continental plates on the surface of the water Making sure they fit together. 4. As the water heats. Watch the action of the bubbles as they rise from the bottom of the pan. Observe everything you can about what happens to them when They rise under a piece of foam and a piece of cork. Notice any differences.

13. Lab - Continental Drift cont. 5. Once the water begins to boil, watch the pieces of foam and cork. How do they move? In what direction do they move? Do they crash into other pieces? What happens when cork and foam crash into each other? Record the answers to your observations in the data table. Be sure to observe the boiling water for a while. It may seem like there is no pattern to the action, but careful observation will reveal certain movements in the boiling water. 6. When you have completed your observations turn the hot plate off and use the tongs to remove the foam and cork pieces from the water. 7. In the data table record any changes in the foam or cork. Have any of the pieces been damaged or melted?

14. Lab - Continental Drift cont. Results: Conclusion: 1. How did you describe what happened to the bubbles as they gathered under The foam? The cork? What happened at the sides of the foam? The cork? 2. What happened to the foam where it crashed into the cork? The cork when it crashed into the foam? 3. What type of natural feature is similar to the action of the bubbles? Explain your answer. 4. Describe the movement of the plastic pieces when the water started to boil. Could you see a pattern? 5. How does this experiment model the moving tectonic plates? 6. How is this experiment different from the real world in terms of tectonic plates? (Hint: What were your foam pieces like after the experiment?) 7. Predict what would happen if the convection currents of the molten magma changed direction or stopped altogether?

15. Plate Tectonics continued

16. More Vocabulary Mid-ocean ridge - longest mt. chain in world, found underwater Sea-floor spreading – way new floor is added to ocean floor Deep-ocean trench – formed where ocean crust bends downward Subduction – process in which ocean crust sinks back into mantle Transform boundary – place where 2 plates slip past each other Divergent boundary – place where 2 plates move apart Convergent boundary – place where 2 plates come together Rift valley – a divergent boundary on land

17. Theory of Plate Tectonics • Canadian scientist observe cracks in crust – J. Tuzo Wilson • Called them plates • Developed theory of plate tectonics – idea that pieces of Earth’s • crust broken up into pieces • Explains formation, movement, and subduction of plates • As plates move they collide, pull apart, grind past each other • Where breaks occur in crust along boundary called faults

18. Have 3 types of boundaries: Transform boundary- plates slipping past each other, crust neither created nor destroyed, is happening in California

19. Convergent boundary – where 2 plates are coming together, called a collision, may bring oceanic crust with oceanic crust (more dense will go under creating a trench),

20. continental with continental (both low dense will squeeze crust into mountain range) or

21. or oceanic with continental (ocean will go under continental back into mantle), density will determine which type of crust winds up on top, oceanic crust made of basalt, is more dense so is usually subducted http://www.pbs.org/wgbh/aso/tryit/tectonics/#

22. Divergent boundary – where 2 plates moving apart, found on land and water most occur at mid-ocean ridge, on land called rift, have rift in New Mexico called Rio Grande Rift, also in Africa where someday may pull eastern part away from rest of continent in ocean have series of volcanoes along ridge, is evidence of sea floor spreading http://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html

23. Sea-Floor Spreading • mid 1900’s able to use sonar to map ocean • discover mid-ocean ridge, place where material from mantle rises, spreads out, pushes old material (rock) to both sides of ridge • called sea-floor spreading by American geologist Harry Hess • new material being added on regular basis (Atlantic Ocean) • when rock pattern studied realized evidence that poles have reversed themselves, last happened 780,000 yrs ago • rocks from sea floor able to be gotten due to sea-floor drilling, age able to be determined • if sea spreading then else where needs to be shrinking (Pacific Ocean) • found at deep-ocean trenches, where ocean floor being subducted down to mantle • result of this constant movement is that about every 200 m.y. ocean is renewed http://www.uwsp.edu/geo/faculty/ritter/glossary/s_u/sea_flr_spread.html

24. Changing Earth's Surface

25. Vocabulary Stress- force that adds potential energy to rock until it changes shape or breaks and moves Deformation – change in rock’s shape or volume Strike-slip fault- rocks on either side slip past each other in a sideways motion, have little up/down motion Normal fault – fault is at an angle Hanging wall - half of fault that is above block of rock Footwall – half of fault that is below block of rock Reverse fault – blocks move in opposite directions of a normal fault Fault block mountain – mountains created by crust moving along normal fault lines

26. Faults and Fault Movement • Movement of plates produces changes in crust • Movement produces powerful forces that push, pull, bend, twist • lithosphere • A change in the rock’s shape or volume is called deformation • Deformation takes place over long period of time • Have 3 types: • shearing • tension • compression • If stress on plate strong enough it breaks creating a fault • When stress builds up along fault line the fault may suddenly break • and slide causing an earthquake

27. Deformation caused by stress Shearing - pushes mass of rock in 2 opposite directions Compression pushes rock together Tension stretches the rock.

28. Fault and Fault Movements - have 3 types Strike-slip fault – rocks on each side of the fault slip past each other sideways Normal fault –fault is at an angle, one block of rock lies above fault while other block lies below fault, movement means hanging wall slips downward

29. Reverse faults – produced by compression, same structure as normal fault blocks move in opposite directions http://www.uoregon.edu/~millerm/faults.html

30. Mountain Building Plate movement causes folding and faulting which results in mountain building. When continental plates collide slowly the layers of rock in the plate fold, and the edges are pushed towards each other. Sometimes the movement causes tension which causes the crust to break forming a normal fault. This faulting may cause mountains to form.

31. Some mountains are the result of volcanic activity. Volcanoes may be found along plate boundaries. There are currently about 600 active volcanoes on land. Many are found along the Pacific Rim or what is called the ”Ring of Fire”. A few develop over what is called a “hot spot”. This is an area where the magma melts through the crust. These are often in the middle of the continental crust or oceanic plate. When on an oceanic plate may form a series of volcanic mountains such as the Hawaiian Islands.

32. Land Subsidence Land subsidence occurs when the land surface sinks, or subsides, as a result of geological movement or human activities. Diverging boundaries can lead to rift valleys or ocean basins. Sometimes one part of crust will rise and the other side will subside. The crust may sink below sea level. Humans may also cause subsidence by with drawing large amounts of water from the ground. As the water is lost underground the rocks and soil settle closer together which means less space used. This will cause the land above to sink or subside. If the land sinks to far flooding may occur during heavy rains. http://ga.water.usgs.gov/edu/earthgwsinkholes.html