GEOS 212 Lecture 2 Outline of Last Lecture 1 Course logistics Introductions Course web page link from D2L Course organization and grading policy Extra credit opportunities 2 Ocean Basins Basics of oceans solid earth and atmosphere Present day ocean basin characteristics Ocean basins thru geologic time plate tectonics Plate tectonics on a short time scale Geologic Time Outline 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 of plates movement of plates and most earthquakes and volcanoes Plate tectonics plates crust uppermost mantle 100km total are rigid and move over a very weak but not molten asthenosphere Plate Boundaries Divergent Convergent Transform Divergent Boundaries aka Spreading Centers Mid Ocean Ridges are where new plate 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 center o 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 general Current Lecture PLATE 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 earth PLATE 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 centigrade ICELAND a place where an active spreading center is on dry land because oceanic crust is thicker there At spreading center continents split apart and eventually the space in between eventually becomes well developed ocean WHAT 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 sea floor because they are hot Divergent boundaries are the longest about 28 000 miles mountain range on Earth