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Lecture 3

Environmental Science
Course Code
Nick Eyles

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Earth history is all about history of the ocean
How continents break up and oceans open
oContinent creates a dome above a mantle rising underneath
continent and pushed up because of warming (outward flow from plume)
creating rifts in all directions of dome...and creates a triple junction-3 major
fractions..(oceanic crust, ocean, failed rift)
oEach of the arms is called a rift..area is going down (subsiding)
oEvolution of the triple junction (only 1 rift opens up-develops into ocean)
oFailed rifts-just sit there, fill up with sediments, sites for oil and gas, buried
and cooked and develop hydrocarbons..petroleum geologists love it
oOne major rift system in atlantic that widened into an ocean
oFailed rifts are preserved in modern continents from break up of pangea
oOttawa river valley, st Lawrence examples of failed rifts
oAmazon, niger, panama, are all rivers now
oFailed rifts important because they control where large rivers flow, generate
quakes (old rifts become activated)
Stage 1: East African rift
oMost of Africa
Stage 2: Red Sea
oDiff btw sea and ocean is ocean has a mid ocean ridge along the center
line..oceans widen all the time and seas sea is actually an
embryonic ocean that widens
Stage 3: Oceans
East African rift is where African plate is torn apart..a plume (east African plume)
Horn of Africa (sumalian plate) is gonna break away from Africa and become a little
piece of continental crust
Triple junction in East Africa : red sea, gulf of Aden, main rift coming down to

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oNext 10-20 mill yrs, there will be an ocean, failed arms (gulf of Aden, main
rift coming down to Africa)
oRifts in south are widening
Red box: Arabian plate moving north (pushed by widening of red sea)
oMountains being pushed up by Arabian plate moving north and colliding with
oBy opening an ocean, pushing plates around
Fissures: cracks in earth crust..magma comes up these fissures..flood basalt (lava
flows going for 10s of km)
Canyon cut through major layers of ash (good because we can date them)
Our species started in east African rift where early hominids lived...Kariandusi
oLayer of hand axes (2 mill yrs old)-dont find debris of the making of hand
oHomohabilis handyman (makes tools)-brain size increases (650 cc brain
capacity...size of small motorcycle)
oWe have cranial capacity of 1200CC (bike BMW)
Most evolutions occur when lakes at max size
Large lakes=lots water, abundance of food
Afar triangle- rift widening by Arabian plate, where lucy comes from
oRight in the triple junction...oceans being built
oDanakil desert-dry area
Shield volcano-low slope angles, lava flows (flood basalts)has basalt eruptions (not
Pointy volcanoes-dangerous, violent eruptions, magma stiff (gas only comes out in
major eruptions)
Flood basalt-lake fills up and overflows and then fills landscape
oBuilding an ocean floor (oceanic crust)
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