GEO 101 1st Edition Lecture 3 Outline of Last Lecture 1 Stellar Nucleosynthesis 2 Solar System Formation 3 Moon Data 4 Earth 5 The Celestial Neighborhood 6 Magnetic Field 7 The Van Allen Belts 8 Aurorae 9 Surface Features 10 Elemental Composition 11 A layered Earth 12 Earth s Interior Layers 13 Uniformitarianism 14 Geological Time Outline of Current Lecture 1 Theory of Plate Tectonics 2 Continental Drift 3 Wegner s Hypothesis 4 Continental Drift Renewed Interest 5 Earth s Magnetic Field 6 Continental Drift Paleomagetism 7 A Scientific Revolution Begins a Seafloor Mapping 8 Plate Tectonics The New Paradigm Current Lecture Plate Tectonics Theory of Plate Tectonics Continental drift hypothesis Seafloor spreading theory Earth s major plates These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Move at slow continuous rate about 5cm yr 2 inches o Cooler denser slabs of oceanic lithosphere descend into mantle Plate Boundaries o Divergent plate boundaries o Convergent plate boundaries o Transform fault boundaries Scientific revolution unfolds Continents in motion Early ideas o Insightful geographers Continental Drift An Idea Before its Time Alfred Wegener First proposed continental drift hypothesis is 1915 Published The Origin of Continents and Oceans Gave list of evidence as to how these continents must have drifted apart Supercontinent Pangaea began breaking apart 2 X 10 8 years ago Pangaea 200 million 2 X 108 years ago Wegner s Hypothesis o Continental drift hypothesis Continents drifted to present positions o Evidence to support hypothesis Fit of continents Fossils Rock type structural similarities Paleoclimate Wegener s Continental Drift hypothesis o Evidence 1 fit of continents How well do they fit Pretty good after 200 million years of change o Evidence 2 Fossil Correlation o Mesosaurus shallow marine reptile Permian 260 ma Evidence 3 rock type structural similarities o Evidence 4 Paleoclimate o The Great Debate Objections Lack of mechanism for moving continents Wegener incorrectly suggested continents broke through ocean crust o Wegener proposed tidal loading forces o Rejected not enough force Strong opposition from all areas of scientific community Alternatives to continental drift hypothesis None of these other theories could account for all explanations not all of it Cooling contracting planet o Only account for some not all of the evidence that the continental drift theory had Geosyncline o Basin fills with sediments o Basin sags o Mantle heads o It rises mountains Above two bullets account for mountains Heating Expanding planet Accounts for separating continents Continental drift scientific method Wegener s hypothesis correct but contained incorrect details A few insightful scientist pursued hypothesis further Continental Drift Renewed Interest Fast Forward 50 years Paleomagneticism Renewed interest from rock magnetism Earth s Magnetic field Has south and north pole Protects earth from solar wind Earth s Magnetic Field Rotation of liquid iron outer core solid iron inner core Outer part of core is magnetic and gives out magneticism and that s how we get our magnetic field Protection from Solar flares digression o Protecting us from burning up from solar flare Northern lights Remnants of a solar flare Continental Drift Paleomagetism Rock magnetism Magnetized Minerals in rocks o Show direction to Earth s magnetic poles o Provide means of determining latitude of origin o Cooling tocks Currie temperature o Rocks have magnetic inclination Magnetized rocks indicate apparent polar wander o The continents move Example o Europe much closer to equator when coal producing swamps existed Polar Wandering o Oldest rocks on bottom newest rocks on top o o o You can look at a series of rocks that have a magnetic inclination and see how they measure It looks like where they point to has changed over time Either pole has been wandering and moving Or Continent that rock is on is moving Pole wandering The breaking of Pangaea We can explain polar wandering better if we move the continents instead of moving the poles o Things start breaking up Deep Time Beyond Pangaea Vast times Millions Billions Appreciation for magnitude is important Many geological processes gradual Cumulative results massive A scientific revolution begins Seafloor mapping o Really getting good details o Finding trenches o Finding ridges o Finding a lot of the drop offs o Finding parts of see floor that we didn t have good information o This is very recent for geological studies Submarine warfare in WWII showed the necessity of a good map of the sea ocean floods o Driven by military submarine warfare 1950s 1960s technological strides permitted extensive mapping of ocean floor o Push for all this information took off o To get better mapping techniques seismic technology game int o Lot more mapping o A lot more sampling o Deeper depth finding and better technology Harry Hess Seafloor spreading hypothesis early 1960s o Studies magnetism of rock s o Sees that magnetism shows reversals in time Geomagnetic reversals o Earth s magnetic field periodically reverses polarity o o We see reversals in earth s magnetism Earth s magnetic field periodically reverses polarity Dates of polarity changes determined from lava flows Geomagnetic reversals seafloor spreading o Recorded in ocean crust o Vine Matthews 1963 tied magnetic striped in ocean crust near ridges to Hess s seafloor spreading Newest rock comes up and as you move away from ridge you get older rock o o Paleomagnetism Strongly supports continental drift seafloor spreading Brand new crust being created Plate Tectonics The New Paradigm Earth s major plates Lithosphere strong rigid outer layer o Uppermost mantle overlying crust o Overlies asthenosphere weak mantle o How does it move o o o o Originally 7 major lithospheric plates Pacific Eurasian North American South American Antarctic Australian Indian African Plates in motion continually changing in shape size Largest plate pacific plate but there are actually 12 major plates and several smaller microplates Most plates include and entire continent large area of seafloor Earth s Major Plates Motion o Slow and continuous o 5 centimeters 2 inches per year o Cooler denser slabs of oceanic lithosphere descend into mantle Earth s Major Plates Boundaries o Plate Boundaries Each plate bounded by combination of the three types of boundaries