1. Happy Valentine’s Day! Weather report Review Plate tectonics Review session: tonight 5-7, Chavez 110

2. Last Time Reversals of Earth’s magnetic field are recorded in cooling volcanic rocks Magnetic striping of the seafloor parallel to mid-ocean ridges (MORs) Glomar Challenger samples seafloor from S America to Africa showing that NEW CRUST is being created at MOR’s!!!

3. Plate Tectonics Overview Rigid outer layer of Earth is broken into pieces which move around relative to each other called tectonic plates or lithospheric plates Lithosphere = crust + little bit of mantle (the rigid part) Plates “float” on mushy asthenosphere All driven by convection in the mantle

4. Plates Interact at Boundaries Divergent – new plate material formed. MORs, continental rift zones. Areas of crustal extension. Spreading centers Convergent – old material recycled as one plate goes under the other. Ocean-ocean, ocean-continent. Crustal compression. Subduction or collisional zones. Trenches Transform – plates slide by each other

5. Mechanical Layers of Earth Lithosphere – “rock sphere” top 100 km, cold, rigid, brittle. Crust + little bit of mantle Asthenosphere – “weak sphere” 100-350 km deep. Layer in mantle that is so hot that it is mushy – deforms easily, low viscosity Mesosphere – “middle sphere” 350-2900 km deep. Rest of mantle. Pressure is so high that rocks retain some strength but still can flow

6. Lithospheric Plates Move relative to each other along plate boundaries Created at divergent boundaries Recycled at convergent boundaries All of the action driven by convection in the mantle

7. Divergent Plate Boundaries “Spreading centers” Mid-ocean ridges, MORs Continental rift zones, rift valleys

8. MORs Longest mountain chain on Earth, about 60,000 km in length Cover about 20% of the Earth’s surface Average height 2.5 km Lots of small, shallow earthquakes, undersea volcanism On land at iceland Black smokers and the origin of life

9. Continental Rifting Crust bulges above rising magma Finally breaks, huge blocks sink into hot, less dense underlying material Rift valley with lakes forms Rifting continues, ocean transgresses New ocean basin, MOR