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Nick Eyles (500)

Lecture 3

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Environmental Science
Nick Eyles

EESA06 Lecture Page 3 EESA06 Lecture 3 How continents Break Up and Oceans Open - Mantle movement creates - Triple junctions – 3 major fractures o Middle of continent, dome forms above plume, o Outward flow from plume creates rifts o Only one rift develops into an ocean - Failed rifts are preserved in modern continents from the breakup of Pangea – they just sit there and may fill up with sediments - Example of failed rifts in Canada: Ottawa river valley and St. Lawrence river valley o Control river flow, generate earthquakes Stage 1: East African Rift - Continent undergoes extension, the crust is thinned and a rift valley forms Stage 2: Red Sea - Continent tears in two, continent edges are fractured and uplifted, Basalt eruptions form oceanic crust Stage 3: Atlantic Ocean - Continental sediments blackout the subsiding “pressure” margins to keep continental shelves, the ocean widens and a mid-ocean ridge develops as in the Atlantic Ocean Difference between a Sea and an Ocean - Ocean has a mid-ocean ridge, and always widening - Seas do not widen East African Rift System - Continental breakup and birth of a new ocean - Somalian plate – the “horn” of Africa will break away and become an ocean - Triple Junction - Gulf of Aden, Red Sea, Lake Turhana (one of these will become an ocean) Arabian Plate - Pushed north by the widening of the red sea Fissures – cracks in the earth’s crust - Basaltic magma comes out thru the fissures, generates flood basalts Ash layers – can put an age on it Early hominids started in East African Rifts – Kariandusi (layer of ash founder hammers) - Homohabilis – tool maker hominids Where is an ocean opening today? - When there are lots of oceans there is lots of food – rich ecosystem, key step of human evolution took place when there were large oceans Afar Triangle – Rift widening, famous for human evolution (Lucy – australopicthin) - Thinned crust, Flood Basalts - Danakil Desert - Shield Volcano – low slope tips, source of flood basalts, basalt eruptions (building oceanic crust) - Pointy Volcanoes – have more violent eruptions , gas doesn’t come out as readily, magma is more stiff 1 EESA06 Lecture Page 3 Deccan Lavas – cause extinctions Margin of the Red Sea – Egypt - Nile river – flowing from East African Rift, Ethiopia, Parallels Red Sea - Giza (old period - pyramids made out of limestone) and Luxor (new period – temples made out of granite) - population clustered around these two places Pyramids: all constructed approx 4,500 years ago 1) Great Pyramid of Khufu (Cheops) – Tura limestone facing stone 2) Khafre’s Pyramid (Chephren) 3) Menkaure’s Pyramid “the idle and foolish exhibition of royal wealth” “soliders, forty centuries of history look down upon you” Bioclastic Limestone – made up of broken fossils (foraminifera – nummulites organisms) - Numismatics – study of coins, they look like coins hence the name Mokkatam Limestone - Thin
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