Plate Tectonics In-Class Test

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plate tectonics

study of formation & movement of earth's plates

lithosphere

crust & upper mantle - solid, brittle rock, behaves elastically (bends then breaks)

asthenosphere

upper mantle beneath lithosphere - exhibits plasticity due to great pressure

plate

solid section of Earth's lithosphere - Earth's broken into ~20 different plates that move in different directions

converge

plate interaction - moving towards one another

diverge

plate interaction - moving away from one another

rifting

divergence on LAND

sliding boundary

plate interaction - sliding horizontally past one another

convection

current w/ circular motion of material due to heating & cooling - ONE of the drivers of plate motion

upwelling

when magma moves up towards the surface

subduction

when ocean crust goes beneath less-dense continental crust, into the mantle

Alfred Wegener

1915, proposed that all continents were once joined in single land mass that started to break up ~250mil yrs ago

Pangaea

supercontinent that started to break up ~250mil years ago

Laurasia

Northern Pangaea

Gondwana

Southern Pangaea

EVIDENCE for continental drift #1 - puzzle

continents fit together like a puzzle - Atlantic coasts of SAmerica & Africa (when you examine the continental margins, they fit together even better)

EVIDENCE #2 - Fossil Evidence

fossils of plant & animal species of the same species found of different continents & no plausible explanation as to how they would cross 3,000mi of ocean - Mesosaurus

EVIDENCE #3 - Rock & Mountain Correlation

no two granites are completely the same (age & composition-wise) - Appalachians & Caledonian Mountains line up & are of the same comp ; identical rock composition & age in Maine & Northern Africa

EVIDENCE #4 - Glacial Evidence

glacial sediment deposits found in places where no glaciers are found today - glacial scratches line up like jigsaw puzzle when continents are reassembled

EVIDENCE #5 - Climactic Evidence

distribution of climate-sensitive sedimentary rocks on different continents - coal deposits found in Antarctica (coal forms in tropical climates from decayed organic matter - Ant. must have at one time been in a tropical climate)

response to continental drift theory

Wegener is RIDICULED! b/c... he was proposing a revolutionary proposal ; was a meteorologist, no respect there ; had no way to explain how plates were actually moving (tried to guess and say the tidal forces of the moon did it but he was wrong)

post-WWII submarine findings

ocean floor mapping 1940s, there are ridges in the middle of most oceans!

Mid-Atlantic Ridge

...a ridge in the middle of the Atlantic. Divergence. Seafloor spreading.

Harry Hess

1962 Princeton geologist, proposed SEAFLOOR SPREADING, centered on mountain ridges

seafloor spreading

as plates move away from each other, new ocean crust is created, plates powered by convection in asthenosphere b/c of divergence & upwelling ... as you move away from Mid-Atlantic Ridge, rocks get older

Why ICELAND is special

it's the only place on Earth where the Mid-Atlanitic Ridge is above sea level!

paleomagnetism

magnetic history of the Earth

polar reversal

about every 500,000yrs, magnetic poles switch when outer core moves in opposite direction

magnetometer

instrument Vine & Matthews used to detect magnetic orientation of minerals in rock - material spreading from oceanic ridge had a N-S-N-S pattern in a mirror image --> polar reversals

Curie point

580degC, temp at which magnetic minerals can no longer move and are magnetically solidified (if rock melted again, its "age" and magnetism would be reset)

hotspots

a plume of magma created deep within Earth around the mantle-core boundary - caused by unequal heating - rises towards surface helping to create volcanoes

Olympus Mons

CRAZY-HUGE volcano on Mars - no chain of volcanoes b/c Mars does not have plate tectonics

Hawaiian Islands

big island = largest, youngest b/c each island forms as plate moves over hotspot -- as islands age, they erode & become smaller

polar wandering

magnetic poles have stayed in ~same location - apparent polar wandering means the plates must be moving

formation of the Alps

movie! - alps formed ~30mil years ago, formed when Africa crunched into Europe and the oceanic crust initially between them buckled, forming jumble of Alp rock as high as 22,000ft (currently eroding away) - top of mountain=African rock ; middle mountain = oceanic rock ; lower mountain = European rock

primary crust

dates back to early solar system, emerged after Mars-sized object smashed into early Earth - some crystals of minerals separated early

secondary crust

forms after heat from decay of radioactive elements gradually accumulates within a planetary body

tertiary crust

forms if surface layers are returned back into the mantle of planet - yields light-colored igneous granties

Mohorovicic discontinuity

deep surface that marks radical change in composition to an extremely dense rock rich in the mineral olivine that underlies both oceans and continents everywhere

oceanic crust

basaltic composition

continental crust

granitic, rhyolitic composition

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