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Dear Excited Experimenters, Today we will review sea floor spreading, the plate boundaries of the world, and your vocabulary homework. Why did I have you match the pieces of a ripped magazine picture? What strategies did you use? What is Wegener’s theory of continental drift?Sincerely,Mrs. Williams
Wegner’s believed that all the continents were connected in one single landmass called Pangaea and have since drifted apart. According to the theory, Pangaea existed over 300 million years ago and when it broke apart, it formed the continents we have today.
http://phschool.com/webcodes10/index.cfm?wcprefix=Cfp&wcsuffix=1015&fuseaction=home.gotoWebCode&x=12&y=10http://phschool.com/webcodes10/index.cfm?wcprefix=Cfp&wcsuffix=1015&fuseaction=home.gotoWebCode&x=12&y=10 PHSchool.com Cfp-1015
What evidence supports the theory of continental drift? http://school.discoveryeducation.com/clipart/clip/ani-cano-gif.html
Mountain ranges in both continents line up • European coal mines line up with coal fields in North America • Plant-like fossils and fresh water fossils of reptiles separated by oceans where reptiles could not have swam these great distances • Tropical plant fossils found in the Artic Ocean formed when land was near the equator • Scratches in bedrock show that glaciers once covered South Africa • The edges of the continents can be matched together.
What was Wegener missing to support his theory? http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm Click to show animations http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_seafloorspreading.html
Wegener could not explain the force that pushes or pulls the continents. • Geologists at that time believed that mountains formed by slowly cooling and shrinking like the skin of a dried up apple. • Wegener proposed that when continents collide, their edges crumple and fold creating huge mountains.
How can scientists detect the ridges under the ocean and why they compare them to the seams in a baseball?
Sonar detects mid-ocean ridges • Mid-ocean ridges curve like the seams of a baseball and extend into all of the Earth’s oceans. • In sea floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result,the ocean floors move like conveyor belts, carrying the continents with them. • Older rock moves out as newer rock is formed.
Most of the mountains in this underwater mountain range lie hundreds of meters below the ocean, but in a few places, they rise above the surface –as they do in Iceland.
Proof of sea floor spreading • Strange rocks shaped like pillows or like toothpaste squeezed from a tube down in the ocean. Such rocks only form when molten material hardens quickly after erupting under water • Magnetic stripes hold a record of the Earth’s magnetic field and they are symmetrical along the mid ocean ridges • Evidence from drilling samples proved that the rocks were older farther away from the ridge and the youngest rocks were always in the center of the ridges. http://education.sdsc.edu/optiputer/flash/seafloorspread.htm Click to see animation of sea floor spreading
Click on the second videoAlvin sub • http://www.pbs.org/saf/1503/video/watchonline.htm?user2=pbs-saf&template2=publishmain.html&query2=*&squery2=squery%3D%252BClipID%3A3%2B%252BVideoAsset%3Apbssaf1503&select=709776&submit2=GO
What is oceanic crust? What rock is found in oceanic crust? What is continental crust? What rock is found in continental crust? What happens when these two plates collide and why?Sea floor spreading is found at what boundary?
Subduction is a process by which the ocean floor sinks beneath a deep ocean trenches and back into the mantle. It takes tens of millions of years. As subduction occurs, crust closer to a mid-ocean ridge moves away from the ridge and toward a deep-ocean trench. The ocean floor plunges into these deep water canyons.
http://www.uky.edu/AS/Geology/howell/goodies/elearning/module04swf.swfhttp://www.uky.edu/AS/Geology/howell/goodies/elearning/module04swf.swf This map shows what happens during subduction. Sea floor spreading happens at a divergent boundary. Look at page 34-35.
Subduction in the Pacific Ocean is happening faster than new crust is added.The Atlantic Ocean only has a few trenches, so the spreading ocean floor has no where to go. In most places the oceanic curst is attached to the continental crust of the continent around the ocean. So as the floor spreads—continent along the edges move. Over time, the whole ocean gets wider. The ocean floor is renewed every 200 million years.
Modeling sea floor spreading activity questions 1. What feature of the ocean floor does the center slit represent? 2. What feature of the ocean floor is missing from the model? 3. How could you modify your model to show an island that formed where a large amount of molten rock erupted from the mid-ocean ridge? 4. How could you show what would happen to the island over a long period of time?
1. The center slit represents the central valley of the mid-ocean ridge.2. The missing feature is the mountainous ridge.3. Draw an island near the start stips. Through the movement, the island’s position would change.4. It would sink below sea level and eventually be subducted. The ocean floor moves like a conveyer belt carrying the continents with them.
What happens when two continental plates collide? What is this boundary called? http://www.free-clipart-pictures.net/mountain_clipart.html
Mountains form! Mountains occur in narrow bands along the edges of a continent when continents collide, their edges fold. Folding continents push up huge mountains. Convergent boundaries Check out this web site to review the meaning of a fold.http://www.uky.edu/AS/Geology/howell/goodies/elearning/module10swf.swf
Boundaries between tectonic plates • Convergent- hint-come together making a connection and colliding the plates. • Divergent- hint-splitting apart and dividing between the plate. This is where rift valleys form. • Transform-hint-like two trains passing in opposite directions. The two plates pass each other moving in opposite directions. Earthquakes happen when the pressure builds up and the plates slide past each other. This is called a fault.
What is a fault? http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm Click to show animations of boundaries
A fault is a break in Earth’s crust where rocks have slipped past each other and they form along boundaries of tectonic plates.
This web site shows the 3 kinds of boundaries: • Convergent boundaries • Divergent boundaries • Transform boundaries http://www.uky.edu/AS/Geology/howell/goodies/elearning/module10swf.swf Click on MODEL and then clip the arrows to show the movement.
http://www.uky.edu/AS/Geology/howell/goodies/elearning/module04swf.swfhttp://www.uky.edu/AS/Geology/howell/goodies/elearning/module04swf.swf
Major volcanic belt formed by the many volcanoes that rim the Pacific Ocean.
What is a hot spot? http://people.colgate.edu/vsimpson/geol220/definitions.htm
http://www.wwnorton.com/college/geo/egeo/animations/ch2.htmClick to see animation of hot spot • A hot spot is an area where material from deep within the mantle rises and then melts, forming magma. When magma reaches the surface, it is called lava. A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.
What did you learn today? Ask me to show you a demonstration of plate boundaries with a box of dirt. Fondly, Mrs. Willtectonicplate
