GEOS 212 Lecture 2Outline of Last Lecture1. Course logistics IntroductionsCourse web page: (link from D2L)Course organization and grading policyExtra credit opportunities2. Ocean BasinsBasics of oceans, solid earth, and atmospherePresent-day ocean basin characteristicsOcean basins thru geologic time  plate tectonicsPlate tectonics on a short time scaleGeologic TimeOutline of Current Lecture Main topics: Layering of Earth: 1) Crust/Mantle/Core (chemistry)); versus 2) Lithosphere/Asthenosphere / Rest of Mantle / Outer Core / Inner Core (mechanical properties) Continent versus Ocean, Continental crust versus Oceanic crust, mantle, lithosphere,asthenosphere (draw diagram) Plate Tectonics explains opening and closing of ocean basins, growth and shrinking ofplates, movement of plates, and most earthquakes and volcanoes. Plate tectonics: plates (crust + uppermost mantle (~100km total) are rigid and moveover a very weak, but not molten), asthenosphere Plate Boundaries (Divergent, Convergent, Transform) Divergent Boundaries (aka Spreading Centers, Mid-Ocean Ridges) are where newplate is created (~5cm/yr); sit ~2km above rest of seafloor because they are warm Diagram of spreading centers -- how oceanic crust is made Animation of spreading centers Video of ocean floor at spreading centero height of spreading center?o length of spreading center?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 water temperature?o big surprise when first discovered? Spreading centers on the World Map => world tour! History of the South Atlantic & opening of new oceans in generalCurrent LecturePLATE TECTONICS- Plates of the earth are not just continents, they have lots of ocean covering them- 200 million years ago: there were hardly any gaps in-between the continents of our earth that are currently spread far apart.- Plates travel only a few inches every year- Plate tectonics: MECHANICAL LAYERING is what is what's relevant. Chemical layering does not have as much bearing on plate tectonics.*See the drawing below for Chemical versus Plate Tectonic (Mechanical) layering for the earthPLATE TECTONICS CONTD- Why does earth have continents?Because continental crust is thicker than oceanic crust, therefore it sits higher on the earth and is higher in elevation than oceanic crust. This is the reason we have continents that are high in elevation and oceans low in elevation.- Below is a picture of continental versus oceanic crust/lithosphere*DIVERGENT BOUNDARIES- two plates (lithosphere) that are moving away from each other while atenosphere flows up to the boundary, cools, and adds on to the old plates, forming a new, young plate.- Older plates are further away from boundary- Oldest sea floor is at the edge of the continents, youngest at boundary- Below is a drawing of a cross-section of a divergent boundary*- Height of the spreading center is 2km above surrounding sea floor- Length of the ridge is 28000 miles long- water is 400 degrees centigradeICELAND- a place where an active spreading center is on dry land because oceanic crust is thicker thereAt spreading center: continents split apart, and eventually the space in-between eventually becomes well developed oceanWHAT WE LEARNED TODAY• Key layers – LITHOSPHERE (= crust + uppermost mantle) and ATENOSPHERE (weak but not molten mantle below lithosphere).• Plates are made of LITHOSPHERE.• Plates are RIDGID.• PLATE TECTONICS is the reason that ocean basins grow and shrink over time.• New plate is CREATED at divergent plate boundaries.• Earth has Continents and Oceans because it has two kinds of CRUST (continental and oceanic) of different thickness.• Divergent boundaries sit about 2 km above the surrounding seafloor because they are hot.• Divergent boundaries are the longest (about 28,000 miles) mountain range on