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Continental Drift Plate Tectonics

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    Continental Drift Plate Tectonics Continental Drift Plate Tectonics Presentation Transcript

    • Continental Drift & Plate Tectonics
    • Continental Drift Theory
      • First proposed by Alfred Wegener in 1912:
        • 250 million years ago, all of the continents were combined into one super-continent called “Pangaea”
        • The continents gradually drifted apart to where they are today
      • Wegner didn’t make up this theory out of the blue – like all scientists, he based it on evidence
    • Evidence Summary
      • Geographic fit of South America and Africa
      • Fossils match across oceans
      • Rock types and structures match across oceans
      • Ancient glacial features
    • Geographic Fit
      • Continents look like they could be part of a giant jigsaw puzzle
      • Here’s how they moved apart
    • Fossils Match
      • Plant and animal fossils found on the coastlines of different continents
    • Fossil Fuel in Antarctica
      • Tropical plant remains (coal deposits) found in Antarctica
        • this is evidence that Antarctica was once much warmer and much closer to the equator, since tropical plants don’t grow in Antarctica today
    • Rock Structures Match Across Oceans
      • Same rock patterns found in South America, India, Africa, Antarctica and Australia
    • Rock Structures Match Across Oceans
    • Ancient Glacial Features
      • Glaciation in Africa, South America, India, and Australia during the same time
    • Ancient Glacial Features
    • Evidence but no Method
      • While Wegener presented compelling evidence, there was still no explanation for HOW the continents drifted.
      • The question remained: “If continents drift, what is making them move?”
    • Sea Floor Discoveries
      • WW II: Military Spending
      • U.S. Navy mapped seafloor with sonar in order to help ships and submarines navigate.
      • They expected to find that the ocean floor was a vast, flat plain. What they found was shocking.
    • Sea Floor Discoveries
      • Instead of miles and miles of flat surface, they found that the ocean floor had:
        • oceanic ridges - submerged mountain ranges
        • fracture zones - cracks perpendicular to ridge
        • trenches - narrow, deep gashes
        • seamounts - drowned undersea islands
    • Sea Floor Discoveries
      • In addition, they discovered that the rocks of the seafloor included only basalt, gabbro, and serpentinite - no continental materials .
      • This suggested that the sea floor was not simply “covered up” continental crust, but was made of different materials and at a different time
    • Sea Floor Discoveries
      • Further study of these rocks led scientists to even more surprising information:
      • The sea floor’s youngest rocks were located right at the ocean ridge – and as you moved away from the ridge in either direction, the rocks got progressively older.
    • Sea Floor Discoveries
    • Sea Floor Discoveries
      • What scientists discovered was that the sea floor was being constantly “recycled.” The youngest rocks were created from magma rising to the surface, hardening and pushing aside the older rock.
      • Scientists called this process “sea floor spreading.”
    • Sea Floor Discoveries
      • So now we know:
        • sea floor is being created at the mid-ocean ridges
        • sea floor is spreading
        • the oldest ocean floor occurs at the coastlines of continents…
      • Why doesn’t the earth get bigger? Where does the ocean floor go? Why doesn’t it get any older?
    • Sea Floor Discoveries
      • The ocean floor is pushed against the continental crust – and because it is denser, it dives under the crust.
      • This process is called subduction
    • Sea Floor Discoveries http://www.youtube.com/watch?v=Zl89Owshdjo
    • The Rise of Plate Tectonics
      • In the late 1950’s, the United States was engaged in The Cold War with the Soviets
      • To keep an eye on Soviet nuclear tests, the U.S. military developed new, advanced seismometers
      • These seismometers were deployed in over 40 allied countries and were recording 24 hrs/day, 365 days/year
    • The Rise of Plate Tectonics
      • Besides nuclear tests, the seismometers recorded every moderate to large earthquake on the planet.
      • Scientists mapped the earthquake data and found something they weren’t expecting:
        • Armed with this high-precision earthquake data, seismologists found that activity happens in narrow bands.
    • The Rise of Plate Tectonics
    • The Rise of Plate Tectonics
      • The discovery of these bands led scientists to understand that the earth’s outer shell is broken into thin, curved plates that move laterally atop a weaker underlying layer.
      • Think of it like a hard-boiled egg: you can put cracks all over the shell of a hard-boiled egg, but the egg is still “whole”
    • Types of Plate Boundaries
      • The interaction of the plate edges with each other can be classified as one of three main types of boundaries:
      • Convergent boundaries
      • Divergent boundaries
      • Transform boundaries
    • Types of Plate Boundaries
      • Convergent: areas of plates that are moving toward each other
        • there are three sub-types of convergent boundaries:
          • oceanic to continental
          • continental to continental
          • oceanic to oceanic
    • Types of Plate Boundaries
      • Divergent: areas of plates that are moving away from each other
    • Types of Plate Boundaries
      • Transform: areas of plates that are sliding past each other
    • Types of Plate Boundaries
      • Here’s an animation of each type of plate boundary
    • Types of Plate Boundaries
    • Types of Plate Boundaries http://www.youtube.com/watch?v=ho21AyKgD00
    • Review the Facts Continental Drift Sea Floor Plate Tectonics 1 pt 2 pt 3 pt 1 pt 2 pt 3 pt 1 pt 2 pt 3 pt Go To Exit Slip
    • Continental Drift 1 pt
      • The scientist who first proposed the theory of continental drift
    • Continental Drift 1 pt Answer
      • Who was Alfred Wegner?
    • Continental Drift 2 pt
      • fossils match across continents and oceans, same rock patterns found on five different continents, mountain ranges match across the Atlantic ocean
    • Continental Drift 2 pt Answer
      • What is some of the evidence Wegner used to support his theory that the continents were once joined?
    • Continental Drift 3 pt
      • Because he had no answer to the question, “If the continents are drifting, what mechanism is causing them to move?”
    • Continental Drift 3 pt Answer
      • Why was Wegner’s theory of continental drift widely ignored?
    • Sea Floor 1 pt
      • ocean ridges, fracture zones, trenches, seamounts
    • Sea Floor 1 pt Answer
      • What did Harry Hess and the US Navy discover when they mapped the sea floor using sonar?
    • Sea Floor 2 pt
      • The process of ocean crust “diving” under other crust into the mantle
    • Sea Floor 2 pt Answer
      • What is subduction?
    • Sea Floor 3 pt
      • The process by which the newest ocean floor is created at mid-ocean ridges, pushing older crust outward
    • Sea Floor 3 pt Answer
      • What is sea floor spreading?
    • Plate Tectonics 1 pt
      • What the earth’s outer shell is broken into
    • Plate Tectonics 1 pt Answer
      • What are plates?
    • Plate Tectonics 2 pt
      • Instrument deployed by US Military to spy on soviet nuclear tests which also detected medium-to-large earthquakes.
    • Plate Tectonics 2 pt Answer
      • What is a seismometer?
    • Plate Tectonics 3 pt
      • The three ways plate boundaries interact
    • Plate Tectonics 3 pt Answer
      • What are convergent, divergent, & transform?
    • Review – Exit Slip
      • Choose what you believe to be the strongest piece of evidence Wegner uncovered to support the idea of continental drift and explain why you think it is the most convincing.
      • If new sea floor is constantly being created, why isn’t the earth growing in size?
      • How did earthquakes help scientists to understand the structure of the earth’s crust?
      • THE FINE PRINT
      • © Jan Parker, 2010 – for purchaser’s classroom use only; please do not distribute. If other teachers in your school like what they see, send them to my website http://www.thesciencevault.com or to my web store http://www.teacherspayteachers.com/Store/Jan-Parker 
      • If you put your classroom materials on a server for your students, please post this presentation in pdf form. Thanks!