Continental Drift

Question 1

who first purposed continental drift?

Answer 1

alfred wegener

Question 2

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

Answer 2

• 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

Question 3

what is continental drift?

Answer 3

continents have moved over time

Question 4

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

Answer 4

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

Question 5

Palaeomagnetism (def.)

Answer 5

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

Question 6

how does paleomagnetism indicate that continents have drifted over time?

Answer 6

-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)

Question 7

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

Answer 7

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

Question 8

paleomagnetism helped us determine the existence of which supercontinent?

Answer 8

pangaea around 200 millions year ago

Question 9

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

Answer 9

-triassic (early)
-jurassic
-creataceous

Question 10

gondwana part of pangaea is now what?

Answer 10

africa, south america, india, australia

Question 11

laurasia part of pangaea is now what?

Answer 11

north ameria, europe, asia

Question 12

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

Answer 12

africa and europe collide
north and south america come closer

Question 13

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

Answer 13

-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

Question 14

what is geomagnetic excursions?

Answer 14

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

Question 15

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

Answer 15

magnetic field helps protect us from radiation

Question 16

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

Answer 16

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

Question 17

what do the presence of magnetic reversals on seafloor indicate?

Answer 17

-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

Question 18

what are the rates of seafloor spreading?

Answer 18

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

Question 19

what are the ways that sea floor spreading was confirmed?

Answer 19

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

Question 20

where are earthquakes and volcanoes concentrated?

Answer 20

-belts/edges of different plates

Question 21

what is the lithosphere?

Answer 21

mostly solid; contains earth’s crust and upper mantle

Question 22

what is beneath the lithosphere?

Answer 22

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

Question 23

what is convergent plate boundary?

Answer 23

plates are moving towards each other on collision course

Question 24

what is divergent plate boundary?

Answer 24

plates are separating from each other

Question 25

what is transform plate boundary?

Answer 25

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

Question 26

why do plates move?

Answer 26

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

Question 27

divergent boundaries (mid ocean ridges) & examples

Answer 27

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

Question 28

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

Answer 28

-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)

Question 29

divergent boundaries (continental rifting)

Answer 29

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

Question 30

convergent boundaries (ocean/continents)

Answer 30

-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

Question 31

convergent boundaries (continents/continents)

Answer 31

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

Question 32

transform boundaries have a lot of stress which causes what?

Answer 32

lots of earthquakes (ex. san andres fault)

Question 33

what are mantle plumes?

Answer 33

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

Question 34

when plates move across mantle plumes what happens?

Answer 34

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

Question 35

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

Answer 35

large igneous provinces