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Continental Drift & Seafloor Spreading Marine Science Chapter 11 Continental Drift: What is it? Idea that all the continents were once joined together. Who came up with the idea? Was he the 1st to think of this? Alfred Wegener No Why did they come up with this idea? Pangaea Theory of Continental Drift Maps- “puzzle pieces” could make Super-continent Wegener called it Pangaea Ocean called Panthalassa He thought it might have taken 200 million years for the continents to split and drift apart to today’s position Is there Evidence? Maps available in 1600’s pretty accurate 1855 Edward Suess of Germany found fossils of Glossopteris (ancient fern) South America Africa Australia India Antarctica How did they get there? Too heavy to travel w/wind, Too fragile to survive sea voyage Is there more? Critters too !!! Animal fossils found on opposite continents Ocean too far for ocean travel Today we also look to Biogeography Like species living on separate continents, but adaptations have changed do to environmental conditions Still more? Coal 1908, Ernest Shackleton discovered coal in Antarctica. How is coal formed? Antarctica MUST have moved Coal formed from vegetation being buried in warm, swampy climates faster than it could decompose What is the temperature like in Antarctica today? Evidences: 3 Jigsaw puzzle Fossil remains (both plant and animal) Coal found in Antarctica Wegener’s Flaw No mechanism for the drift Wegener’s theory did not include a strong enough account for how the continents could move No credibility He suggested Earth’s rotation & tides moved them Calculations would prove otherwise He was a meteorologist, not a geologist Jigsaw puzzle theory had gaps He died B-4 theory was accepted Disappeared in 1930 in Greenland Lab “Dance of the Continents” Read as a class Work in pairs Turn in when complete Theory of Seafloor Spreading Chapter 11 Meteor- German expedition Mid-Ocean Ridges Rift Valleys Deep valleys running through mid-ocean ridges Trenches Mountain ridges on bottom of ocean Ravines in seafloor Patterns were revealed………. Hess and Deitz- 1960 SFS Seafloor is constant state of creation and destruction New crust emerges at the mid-ocean ridges Magma pushes up through rift and solidifies into new crust New sea floor forms at the ridges, and is then subducted at the trenches (goes back into the rock cycle) What are the evidences? If this is true, where would you find older rock; trenches or ridges? Radiometric dating If this is true, where is the more dense rock? Older is farther away from ridges- trenches Newer rock will have less deposits on it- more dense, more layers, older rock is at the trenches If this is true, magnetism should be symmetrical Huh? Plate Tectonics combines Continental Drift and Seafloor Spreading P.T. state that Earth has over 12 plates that float on top of the Asthenosphere 2 different types of plates Oceanic; more dense Continental; less dense These plates interact in 3 different ways: Divergent BoundariesConvergent BoundariesTransform Faults- So what happens? Divergent boundaries- Plates move away from one another- Constructive Boundaries Ridges, valleys, new seafloor; much activity here Mtns can form higher than sea level Iceland Transform (fault) boundaries- Plates slide past each other- Earthquakes prevalent San Andreas Fault in Ca; Pacific/N. American Plates Divergent Boundary- Constructive Transform Fault/Boundary Cntd Convergent Boundary Convergent boundary- 2 plates meet; collisionsDestructive Boundaries 2 ocean plates; 1 subducts under the other Island arcs result Japan, Aleutian Islands Ocean and continental: more dense oceanic subducts under less dense continental Subduction occurs in trenches Range of vocanic mtns: Benioff’s Ring of Fire, Andes Mtns, Cascades (Mt St Helens) 2 continental plates: equal densities push mass together and up Himalayans 2 Oceanic Plates Oceanic meets Continental Continental meets Continental Plate Movement What is the mechanism behind continental drift? Convection! Warm air rises, then falls as it cools, rises at it warms, etc. etc. Convection currents exist w/in mantle; moves plates away from each other at divergent boundaries, towards each other at convergent boundaries, past each other at transform boundaries Second mechanism is seafloor spreading- plates slide away from ridges Lab: “Dance of the Plates” Read as a Class Work in Pairs Turn in When Complete Hot Spots? Activity: Grab a Text; w/partner (no more than 2) How did volcanoes arise away from plate boundaries? Diagram the creation of the Hawaiian Islands Explain how it works Why is it not one large continent but many islands Look at Earth at the following: 225 MYA, 135 MYA, 100 MYA, 65 MYA, and today. Compare them, and be able to recognize each for test purposes Activity: Using ONLY your notes, complete the W/S in class. Due before class is over Wrap it Up!! Continental Drift to Plate Tectonics Video Study Guide Tomorrow Video Clip Activity: Go over W/S Create a brochure explaining the way in which plates move (divergent, convergent, transform). Be sure to include: Mid ocean ridge, trench, continental plate, oceanic plate, rift valley, mid ocean ridge mountain range. Exam Tuesday!!! Use W/S as Study Guide Ring of Fire Class Discussions Research Time Be sure to complete W/S today I will check it off today, we will discuss tomorrow