Geos 212 Lecture 2 08 29 2014 Plate tectonics Earths surface has divided into 10 15 rigid plates pieces of earths crust and mantle move around relative to each other Named after which continent they are under What s a plate Plates are rigid lithosphere o They move because asthenosphere is mushy Geochemical density layers Crust low density materials Mantle high density materials Core metals iron nickel Physical layers Lithosphere crust uppermost mantle o Rigid layer plate o 100km thick asthenosphere within the mantle o mushy like silly putty can flow o 100km thick lower mantle o rigid 2500 km thick outer core o liquid inner core o solid only need to know crust mantle litho asthenosphere temperature of earth cool hot as you get deeper towards core it gets hotter Lecture 2 Two types of crust 08 29 2014 Continental crust vs Oceanic crust Shelf part of continents that are below surface underwater Continental Crust 30 35 km thick granite lower density Oceanic Crust 7 km thick basalt higher density in pic below lithosphere should only go up to ocean floor not ocean surface Granite low density Basalt high density lecture 2 Plate tectonics Plates are moving 3 types of Plate Boundaries 1 Divergent moving apart 2 Convergent moving toward one another 3 Transform Sliding by each other past eachother 08 29 2014 08 29 2014 Divergent Boundary Spreading Center Mid Ocean Ridge part between crusts that split apart plates move apart divergent create new oceanic crust as ocean crust diverges magma rises basalt through gaps Plates usually have both oceanic and continental crust Movie mid ocean ridge Height of spreading center 2 miles off the seafloor Length of spreading center Continues over 28 000 mile largest mountain chain on earth Water temperature 100 degrees centigrade at surface turns to steam 400 degrees centigrade underwater remains liquid Big surprise found living creatures discovered life Thought all life on earth needed sun but it was discovered that it didn t when they found certain life on the bottom o Pompeii worms only known creatures to live in that hot of water 80 degrees centigrade o Tubeworms live without sun they are packed full of specialized bacteria that derive energy from the sulfides pouring from the vents Iceland only place where mid ocean ridges are above land Lots of volcanoes in Iceland Rock is made of basalt Triple Junction Place on earth where 3 plates are pulling apart lecture 2 08 29 2014 Why do plates move Convection cells When you heat material it expands takes up more volume so its density goes down Driven by heat rising in the mantle How did the south atlantic begin to open When did it begin to open 4 step process how an ocean basin conforms 1 rift begins 2 rift valley 3 linear sea 4 mature ocean How do we determine when the spreading began fossils compare when they were both on South America and Africa date the age of ocean floor o rocks on the ocean floor were formed 140 mil years ago Age of the ocean floor Oldest ocean crust is between 180 200 mil years old 08 29 2014 How to calculate rate of spreading Rate distance time o Example Measure of distance 7000km measure of time 140 my o My million years o Rate distance time 7000km 140 my 50km my 5 cm yr divide by 10