Continental Drift Flashcards
who first purposed continental drift?
alfred wegener
what was some of things wegener observed that made him think that the continents had drifted?
- 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
what is continental drift?
continents have moved over time
what was the key characteristic of solid materials that made drift possible?
solid materials could flow like putty (matter of time and scale)
Palaeomagnetism (def.)
the study of the Earth’s magnetic field preserved in rocks
how does paleomagnetism indicate that continents have drifted over time?
-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)
what is polar wander curve and connection to the continenetial drift?
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
paleomagnetism helped us determine the existence of which supercontinent?
pangaea around 200 millions year ago
pangaea existed when? started to break when? the continents we know now formed when?
-triassic (early)
-jurassic
-creataceous
gondwana part of pangaea is now what?
africa, south america, india, australia
laurasia part of pangaea is now what?
north ameria, europe, asia
50 million years in the future, what the main changes to the continenets we expect?
africa and europe collide
north and south america come closer
what is magnetic reversal? what is the effect on rocks?
-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
what is geomagnetic excursions?
like magnetic reversal but not permanent change of large scale field ; usually short-lived of change with variation of up to 45 degrees
geomagnetic reversal and excursions pose a risk to the earth in what way?
magnetic field helps protect us from radiation
when and what was the laschamp excursion/adams event? effect on earth?
-42000 years ago
-reversal of earth magnetic poles
-extinction of neatherahals, austrialian mega fauna, appearance of cave paintins (red ochre used as sunscreen & paint)
what do the presence of magnetic reversals on seafloor indicate?
-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
what are the rates of seafloor spreading?
0.5 cm/year to 20 cm/year
-on average 3 km^2 of new sea floor added every year
what are the ways that sea floor spreading was confirmed?
-dating seafloor with fossils
-dating seafloor with rocks
-oceanic crust youngest at ridges and gets older way from ridges
-sediments thicker in older rocks
where are earthquakes and volcanoes concentrated?
-belts/edges of different plates
what is the lithosphere?
mostly solid; contains earth’s crust and upper mantle
what is beneath the lithosphere?
asthenosphere; plastic layer that plates can move over (plates carry the continents
what is convergent plate boundary?
plates are moving towards each other on collision course
what is divergent plate boundary?
plates are separating from each other
what is transform plate boundary?
plates slide horizontally past each other (needed for spherical planet)
why do plates move?
convection
-rising hot magma build lithosphere at ocean ridges and as it cools, it spreads away. eventually it sinks back into mantle = remelting
divergent boundaries (mid ocean ridges) & examples
magma from asthenosphere reach ocean floor and cool forming new lithosphere
- mid atlantic ridge -> currently pulling iceland apart
divergent boundaries (sea floor spreading) + reason why this is good candidate for origin of life
-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)
divergent boundaries (continental rifting)
-characterized by long rift valleys and basalt eruptions, sometimes allows for new ocean basin to open up
convergent boundaries (ocean/continents)
-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
convergent boundaries (continents/continents)
-two landmasses come together, too buoyant to sink so crust thicken = mountain ranges (ex. himalayas)
transform boundaries have a lot of stress which causes what?
lots of earthquakes (ex. san andres fault)
what are mantle plumes?
jets of hot material rising from deep in the mantle; they are stationary
when plates move across mantle plumes what happens?
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
mantle plumes also cause these characteristic ( associated with lots of major extinctions)
large igneous provinces
