Objectives Explain how paleomagnetism provided the definitive evidence for continental drift. Define seafloor spreading. Define theory of plate tectonics. Describe the different types of plate margins. Explain the role of mantle convection in plate tectonics.
A Revolution in Geology Continental drift Proposed by Alfred Wegener Slow, lateral movement of continents along Earth’s surface The puzzle piece argument Pangaea Continental shelf Continental slope
Matching Geology Matching rocks What is the “true” edge of a continent?
Matching Geology Matching rocks How well do the continents fit?
Matching Geology Matching rocks How well do the ages match?
Matching Geology Matching rocks What evidence did the glaciers leave?
Matching Geology Matching fossils What evidence did the glaciers leave? Glossopteris: ancient tree with large seeds found on several continents Mesosaurus: small reptile found in Brazil and S. Africa
Apparent Polar Wandering Paths Paleomagnetism Apparent polar wandering Magnetic poles wandered Used to indicate America and Europe were a single continent
Seafloor Spreading The missing clue Seafloor spreading The process by which the seafloor splits and moves apart along a midocean ridge New oceanic crust forms along the ridge Global Positioning Systems (GPS) valuable tool
The Plate Tectonic Model Plate tectonic The movement and interactions of large fragments of Earth’s lithosphere (i.e. plates) Below lithosphere- asthenosphere Weak due to hot temperature (near melting point) Relationship between lithosphere and asthenosphere is isostasy Fault A fracture in Earth’s crust along which movement has occurred
Types of plate margins Divergent margins A boundary along which two plates move apart from one another
Types of plate margins Convergent margin A boundary along which two plates come together
Types of plate margins Subduction zone A boundary along which one lithosphere plate plunges into the mantle beneath another plate “Collision zone” between continents Deep oceanic trenches Arcs of volcanoes
Types of plate margins Transform vault A fracture in the lithosphere where two plates slide past each other
Earthquake and plate margins Earthquake Tectonic movement produce pressure and friction. Friction is overcome, the block slips and pent up energy releases with a huge “snap” Focus Where earthquake begins Epicenter Point on earth’s center directly over the focus
The search for a mechanism Earth’s internal heat Conduction Slow release of heat Convection A form of heat transfer in which hot material circulates from hotter to colder regions, looses its heat, and then repeats the cycle
The tectonic cycle Tectonic cycle Movements/ interactions by which rocks are cycled from the mantle to the crust and back Includes earthquakes, volcanism, and plate motion, driven by convection in the mantle As a result, seafloor recycles itself every 200 million years
Critical Thinking What are some of the important questions about plate tectonics that remain unanswered today? Why do geologists call plate tectonics a “unifying theory”? As Africa slowly separated from Arabia, and the sea began to enter the rift, what kind of sediment would you expect to be deposited?