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Follow the key below to positively participate in class today: • All information in () is the instructor “speaking” to you – this does not need to be written down. • All information in LIME GREEN – main ideas – should be written to the LEFT of your divided page notes • All information in YELLOW – details – should be written to the RIGHT of your divided page notes Setting up your notes • 1 (Get a lined piece of paper) • 2 (Fold the left side 1/3 of the way in to create a column to the left.) • 3 (Put the heading at the very top – NAME -DATE -BLOCK) • 4 (Title your notes “Plate Tectonics”) • 5 – REMEMBER: • LIME GREEN – LEFT • YELLOW - RIGHT Looking at the world map, what do you notice about the shape of the continents? Jot down your ideas on your paper… Layers Review The lithosphere is divided into a number of large and small plates and the plates are floating on the asthenosphere Lithosphere = the Earth’s crust plus the upper portion of the mantle layer Alfred Wegener • Early 1900’s - German scientist – expertise in weather/climate • Theorized that continents shift and slowly move over long periods of time • Coined the term, Pangaea • Theory NOT accepted during his lifetime – could not prove how they moved (missing link) Small error in Wegener’s theory • NOT the continents that are drifting, it’s the PLATES • PLATES are composed of both oceanic and continental crust • FAULTS – the cracks between each plate (Notice the plates contain oceanic and continental crust) Plate motion based on The Global Positioning System (GPS) Evidence of Continental Drift Theory (Write these four topics with THREE SPACES in between) 1. Fossils 2. Landforms 3 .Climate 4. Puzzle fit (Now, with your buddy, DESCRIBE these four topics on the right side.) Evidence o Minerals, fossils, and mountains on now different continents match if the continents were together The Mystery of Brachiosaurus (~3 min) Evidence o Glaciation patterns indicate a common ice cap at the South Pole o Pangaea began to split apart 200 million years ago o Diagram Laurasia Pangaea Gondwanaland North America Greenland Eurasia West G. East G. Africa S.America Antarctica Australia India 5. Seafloor spreading • Mid-ocean ridge – underwater mountain chains that run through all of Earth’s ocean basins • Oldest crust near the borders, newest crust in the center • New ocean floor crust is being created at the midocean ridges Speed of Spreading Atlantic Ocean – 2-3 cm/year South Pacific Ocean – 15-18 cm/year What evidence do we have to support this idea of seafloor spreading? o Midocean ridges are warmer than surrounding ocean floors o Active volcanoes on ridges, earthquakes on ridges o Midocean ridge rocks are younger than surrounding ocean floor rocks o Midocean ridge volcanoes are younger than volcanoes further away 6. Magnetic Reversals • most important evidence for seafloor spreading is recorded magnetic reversals in the ocean floor • magnetic minerals in molten rock provide clues to the magnetic reversal of the poles • final, concrete proof that the seafloor is spreading AND plates are drifting Polar Reversal Magnetism Magnetic Poles Magnetic Field Reversals—2:54 HOW do the plates move? Convection Currents • Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creates convection currents beneath the plates that cause the plates to move. Heat Transfer Three Main Types: Conduction Radiation Convection Conduction • Transfer of heat by direct contact • Conductors – the better the conductor the faster the heat transfer • Ex) • egg frying in the pan • Hand on the fire Radiation • Heat transfer through empty space • Ex) sun – common source of heat Convection • Heat transfer through the movement of “fluids” • ex)boiling water, earth’s asthenosphere Plate Boundaries Divergent boundary: Divergent Boundaries • Boundary between two plates that are moving apart or rifting • RIFTING causes SEAFLOOR SPREADING Plate Boundaries Divergent boundary: o Plates are moving away from each other o Midocean ridges are created and new ocean floor plates are created Features of Divergent Boundaries • Mid-ocean ridges • rift valleys – Great Rift Valley, East Africa • fissure volcanoes Leif the Lucky Bridge Bridge between continents in Reykjanes peninsula, southwest Iceland across the Alfagja rift valley, the boundary of the Eurasian and North American continental tectonic plates. Transform Fault Boundary Plates are neither moving toward nor away from each other, they are moving past one another. Transform Fault Boundary The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas Fault) Transform Fault Boundaries • Boundary between two plates that are sliding past each other • EARTHQUAKES along faults San Andreas Fault San Andreas Fault, CA Convergent Boundary: plates are moving toward each other and are colliding (3 types) Convergent Boundaries • Boundaries between two plates that are colliding • There are 3 types… Type 1 • Ocean plate colliding with a less dense continental plate • Subduction Zone: where the less dense plate slides over the more dense plate • VOLCANOES occur at subduction zones Andes Mountains, South America When Ocean Plates collide with Contintental Plates • Create subduction zones, trenches • Create near coast volcanoes • Benioff shear zones (a pattern of earthquakes as an ocean plate grinds down the underneath side of a continent) Benioff Shear Zones Type 2 • Ocean plate colliding with another ocean plate • The less dense plate slides over the more dense plate creating a subduction zone called a TRENCH Aleutian Islands, Alaska When ocean plates collide with other ocean plates Island arcs are created (a pattern of volcanic islands created from a subduction zone that is located off the coast) Type 3 • A continental plate colliding with another continental plate • Have Collision Zones: –a place where folded and thrust faulted mountains form. When a continental plate collides with another continental plate • Mountain ranges are created • (example: Himalayan Mountains) Himalayan Mountains Mountains 2:46 So is the Earth getting bigger? So is the Earth getting bigger? o No o Plates are destroyed as fast as they are created (2 ways) o Plates may be subducted and melted or may be pushed upward to form mountains What causes this? Convection currents within the mantle The up-welling leg of the current creates a divergent boundary which produces midocean ridges The down-welling leg of the current creates one type of convergent boundary that results in trenches and a subduction zone