Continental Drift Flashcards

1
Q

who first purposed continental drift?

A

alfred wegener

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2
Q

what was some of things wegener observed that made him think that the continents had drifted?

A
  • africa and south america fit together well
    -evidence of glacation in tropics
    -evidence of desert sands in temperate regions
    -evidence of tropical plants in antarctic
    -fossils of animals/plants in geographically separated regions
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3
Q

what is continental drift?

A

continents have moved over time

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4
Q

what was the key characteristic of solid materials that made drift possible?

A

solid materials could flow like putty (matter of time and scale)

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5
Q

Palaeomagnetism (def.)

A

the study of the Earth’s magnetic field preserved in rocks

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6
Q

how does paleomagnetism indicate that continents have drifted over time?

A

-basalts & gabbros have ferromagnesian minerals that are wealky magnetic at surface (cool) temperaturs and not magnetic at hot temp. As magma cools below curie point , the Fe minearls align along magnetic field (they retain paleomagnetism unless heated)
-minerals align with magnetic field which run N-S, and dip with latitude so you can determine the location of rock when it was magnetized (in respect to magnetic north)

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7
Q

what is polar wander curve and connection to the continenetial drift?

A

rocks on different ages on single continent look like they are pointing to different magnetic north; looks like pole wander with time but actually continents moved while pole remained static

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8
Q

paleomagnetism helped us determine the existence of which supercontinent?

A

pangaea around 200 millions year ago

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9
Q

pangaea existed when? started to break when? the continents we know now formed when?

A

-triassic (early)
-jurassic
-creataceous

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10
Q

gondwana part of pangaea is now what?

A

africa, south america, india, australia

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11
Q

laurasia part of pangaea is now what?

A

north ameria, europe, asia

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12
Q

50 million years in the future, what the main changes to the continenets we expect?

A

africa and europe collide
north and south america come closer

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13
Q

what is magnetic reversal? what is the effect on rocks?

A

-N/S magnetic pole swap
- rocks crystallizing when magnetic orientation is the same as today = normally magnetized
-rocks crystallizing when magnetic orientation is the opposite as today = reversely magnetized

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14
Q

what is geomagnetic excursions?

A

like magnetic reversal but not permanent change of large scale field ; usually short-lived of change with variation of up to 45 degrees

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15
Q

geomagnetic reversal and excursions pose a risk to the earth in what way?

A

magnetic field helps protect us from radiation

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16
Q

when and what was the laschamp excursion/adams event? effect on earth?

A

-42000 years ago
-reversal of earth magnetic poles
-extinction of neatherahals, austrialian mega fauna, appearance of cave paintins (red ochre used as sunscreen & paint)

17
Q

what do the presence of magnetic reversals on seafloor indicate?

A

-alternating symmetrical patterns of normally and reversely magnetized rocks on mid ocean ridges
-indicates that new sea floor is added at ocean ridges that are magnetized -> can date the magnetized bands and calculate seafloor spreading rate

18
Q

what are the rates of seafloor spreading?

A

0.5 cm/year to 20 cm/year
-on average 3 km^2 of new sea floor added every year

19
Q

what are the ways that sea floor spreading was confirmed?

A

-dating seafloor with fossils
-dating seafloor with rocks
-oceanic crust youngest at ridges and gets older way from ridges
-sediments thicker in older rocks

20
Q

where are earthquakes and volcanoes concentrated?

A

-belts/edges of different plates

21
Q

what is the lithosphere?

A

mostly solid; contains earth’s crust and upper mantle

22
Q

what is beneath the lithosphere?

A

asthenosphere; plastic layer that plates can move over (plates carry the continents

23
Q

what is convergent plate boundary?

A

plates are moving towards each other on collision course

24
Q

what is divergent plate boundary?

A

plates are separating from each other

25
Q

what is transform plate boundary?

A

plates slide horizontally past each other (needed for spherical planet)

26
Q

why do plates move?

A

convection
-rising hot magma build lithosphere at ocean ridges and as it cools, it spreads away. eventually it sinks back into mantle = remelting

27
Q

divergent boundaries (mid ocean ridges) & examples

A

magma from asthenosphere reach ocean floor and cool forming new lithosphere
- mid atlantic ridge -> currently pulling iceland apart

28
Q

divergent boundaries (sea floor spreading) + reason why this is good candidate for origin of life

A

-seawater over basalt reacts and becomes metal rich; re-surfaces in black smokers (300 C) and then meets cool seawater and precipitates minerals
-rich in minerals, organisms live oof heat and gases not sunlight (lithotrophic)

29
Q

divergent boundaries (continental rifting)

A

-characterized by long rift valleys and basalt eruptions, sometimes allows for new ocean basin to open up

30
Q

convergent boundaries (ocean/continents)

A

-continents lower in density than iron rich mantle and ocean lithopshere is similar in density to asthenosphere so it is forced under continents (akas subduction)
-forms andesite volcanoes and mountains

31
Q

convergent boundaries (continents/continents)

A

-two landmasses come together, too buoyant to sink so crust thicken = mountain ranges (ex. himalayas)

32
Q

transform boundaries have a lot of stress which causes what?

A

lots of earthquakes (ex. san andres fault)

33
Q

what are mantle plumes?

A

jets of hot material rising from deep in the mantle; they are stationary

34
Q

when plates move across mantle plumes what happens?

A

you get a progressive trail of volcanoes on earth surface (ex hawaii) aka hot spots that allow you see a progressively older volcanoes that record the movement of the plate

35
Q

mantle plumes also cause these characteristic ( associated with lots of major extinctions)

A

large igneous provinces