Monterey Bay: A Case Study in Environmental Science and Policy ENVS 282 McCormick 2/3/2015 Lecture 2: Earths Structure & Plate Tectonics Instructor Information Instructor: Mary McCormick Office Hours: Tuesday, 4:00 to 5:00 pm or by appointment Bldg 53 (Chapman), 2nd Floor, Room E210 Warm - Up 1. Who is considered to be the father of oceanography and what was one thing he was famous for? 2. What is the biggest reservoir of water on Earth? 3. What is the major difference between the northern and southern hemisphere discussed in class last week? Section 2.1 Earths Interior 5 Earthquake waves reveal Earths structure Arrival times of seismic waves Speed depends on chemistry, density and physical state (solid, partially molten, molten) 6 Types of waves P waves Compressional First to arrive Solid, Liquid, Gas S waves Shear 2nd to arrive Solid 7 Model 2Model 1 8 Lithosphere and Asthenosphere The layers Lithosphere Crust and upper mantle fused together Asthenosphere Deformable region in the mantle Mesosphere Solid lower mantle 9 Earth has layers having different strengths and physical properties Isostatic Adjustment Mechanism by which areas of Earths crust rise or subside until their masses are in balance, floating on the mantle Less dense crust sits higher than more dense crust. Isostatic Adjustment Continental vs. Oceanic Crust *Igneous RockRock that forms from the solidification of molten magma Section 2.1 History of a Theory: Continental Drift 14 Evidence of Continental Drift 15 Evidence of Continental Drift Section 2.3 Evidence for a New Theory: Seafloor Spreading Linking Continental Drift to Plate Motion: Harry Hess Hess developed the seafloor spreading theory: -New molten rock emerges from the mid ocean ridges, spreads sideways as new seafloor, and is subducted back into trenches - process driven by mantle convection* 18 Harry Hess and Seafloor Spreading Seafloor Spreading Spreading centerssite of new crust formation; at ocean ridges Subduction zones site of crust destruction; at ocean trenches Seafloor spreading provided basis for plate tectonics theory 20 Distribution of earthquake epicenters heat flow sediment age, and thickness Paleomagnetism Evidence for Crustal Motion 21 Evidence of Plate Motion: Paleomagnetism (p. 63) Paleomagnetism: The study of Earths ancient magnetic field Rocks retain signature of magnetic field Newly formed rocks are embedded with either normal or reversed polarity (as they solidify) Polarity reversals detected throughout time 23 Late 1960s: Radiometric dating of deep ocean rocks Symmetric pattern of age distribution about mid-ocean ridges Oldest ocean floor only 180 million years old Evidence of Plate Motion: Radiometric Age Dating (ch 1, p ) Plate Tectonics On what lithospheric plate do we reside? By what type of plate boundary do we live? About how quickly and in what direction is our part of our plate moving? 27 Lithosphere is Broken into Plates 28 3 Types of Plate Boundaries Divergent boundary Mantle upwelling Layers of oceanic crust Convergent boundary Plates collide Often subduction Transform boundary Plates slide past each other Usually offset segments of ocean ridges 29 30 31 32 33 Convergent Plate Boundary Features: Subduction Zones Subduction Zones: the sloping area from the trench along the downward-moving plate Convergent Plate Boundary Features: Volcanic Arcs Volcanic Arc: an arc shaped row of active volcanoes. Can occur as a row of islands or mountains Divergent Plate Boundary Features: Mid-Ocean Ridge 37 Intraplate Features: Hotspots Intraplate Features Seamounts underwater volcanoes Tablemounts or guyots Seamounts with flattened tops During the infamous Voyage of the Beagle Darwin observed many coral reefs in different phases. These observations supported his theory of atoll formation Coral Reef Development Fringing reefs develop along margin of landmass Barrier reefs reef separated from landmass by lagoon Atolls reefs continue to grow after volcanoes are submerged "You can explain a lot of the variety you see just by combining these various processes -- the sinking of islands, the growth of reefs, and the last few million years of sea level going up and down rather dramatically," (Perron 2014) Fluctuating sea level emerges as important factor in shaping atoll formation: Life on low-lying atolls: Kiribati In 2013, President Tong has spoken of climate-change induced sea level rise as "inevitable". "For our people to survive, then they will have to migrate Life on low-lying Atolls: Kiribati according to the projections, within this century, the water will be higher than the highest point in our lands (Tong 2014) Life on low-lying atolls: Marshall Islands/The-Marshall-Islands-Are- Disappearing.html?module=Promotron&region=Body&a ction=click&pgtype=article Reminders Reading: Sverdrup Ch. 3 Problem Set 1 is due to ilearn at noon 2/5 Quiz #1 in class 2/9