continental drift + plate tectonics Flashcards
what is a continental drift?
continents moved and rotated over geological time
why did alfred wagner think continents work?
- a jigsaw puzzle
- glaciation in places now located in the tropics, warm things like coal are up in the artics now
- desert sands in area that now have moist, temperate climates
- remains of the tropical plants in the antarctic
- fossil remains of plants and animals that lived in restricted areas but now are widely separated geographically
since the rocks (continents) are very similar, this shows proof they?
were likely joined together
the continents were once _____, and then what happened to them?
was one giant ice sheet that eventually broke up and spread them apart
In 1950 - 1960, the idea revived about continents moving by scientists studying?
strength of rocks, earth’s magnetism and ocean floor
if the continents solid and mantle solid, how can it move?
time, temperature and scale / pressure!!!
ex: ice: they have intricate ice sculptures in ice, but the ice can melt into glacier streams
how does the magnetic field circle the earth (direction)?
out and around
what did blackwell think the source of magnetism is?
- thought it had something to do with spinning
- outside sphere spins faster than inside
- theory was wrong
what is paleomagnetism?
rocks pointing the same direction ended up being different in magnetism patterns in one place than in another
what is the curie point?
atoms stop bouncing when cooled, and atoms will record direction of magnetic field when it passes through that temperature
earths magnetic field will arrange the particles direction in terms of?
the sediments direction
the lines of force at pole go in what direction?
straight up and down
polar wander curves show?
the paths of a magnetic pole with respect to a given continent
what showed proof that the continents had moved?
same age rock: measure which way north pole is pointing
- different continents were not pointing toward the same pole
- should be pointing toward the same pole
- proof continents had moved
what is magnetic reversal?
magnetic north has changed throughout time
earths magnetic field periodically switches signs
ex. 1927: matuyama was hiking across a volcano carrying a compass, and found that the compass pointer flipped on each layer of rock
what are excursions?
when the magnetic field almost switches signs, but didn’t
how long does it take for switches to take place?
3000 - 4000 yrs
the megntic field was probably zero at sometime, what would this have done to the earth?
we would be bombarded from harsh radiation
what are geomagnetic reversals?
magnetic field collapsed for awhile, but did not quite switch
what happens if there is no magnetic shield?
carbon 14 will be more abundant
O2 molecules will create ozone
how do we create a new seafloor?
magnetic reversals: magma chills, freezes in magnetism of that day
the creating of a new sea floor in terms of magnetic reversals is what kind of pattern?
predictable: it is symmetric on both sides
seafloor spreading explains the?
magnetic patterns on the sea floor
seafloor spreading explained by magnetic patterns on the sea floor was first published in what journal?
nature
what can seafloor spreading rates vary between (in cm/yr)?
0.5 - 20
how many square kilometers of sea floor are created each year?
3
how was sea floor spreading confirmed?
- dating through study of fossils
- dating of rocks sampled by seafloor drilling
- crust is youngest at ridges
- sediment thicken away from ridge
the ship that drilled the mantle on the seafloor is called the?
glomar challenger
in 1968, our new paradigm formed to explain why continents are moving and midocean ridges are spreading. what is it called
plate tectonics
what is the theory of plate tectonics?
distribution of volcanoes and earthquakes are not random, and earthquakes follow mid-ocean ridges.
how are plate tectonics created?
- deep inside the earth is hot, as you approach the surface it is cool.
- upper mantle is chilled, therefore brittle. lower mantle is hot, so it is soft.
- this division creates plates, as the soft, gooey stuff underneath pushes the solid, brittle plate
the outside layer that sits on the soft asthenosphere is called the?
lithosphere
what is the plastic layer beneath the lithosphere?
asthenosphere
how do plate tectonics express itself? how does this process occur?
through rising
as it cools, thickness of plate grows, gets denser, heavier, and sinks
what is the convergent plate boundary?
plates move toward one another on a collision course
what is a divergent plate boundary?
plates separate one another
what is the transform plate boundary?
plates must rub against another / slide past another
what is a de fuca plate?
tiny plate broken off
why do plates move?
convention
rising ht magma under mid-ocean ridges builds up in new lithosphere, which cools as it spreads away, and eventually sinks back into the mantle where it is melted
what crest is the sea floor created at?
mid-ocean
in divergent boundaries with sea floor spreading, how are the different layers created?
- seawater circulates through hot basalts
- basalt heated and reacts with rock
- rock becomes metal rich
- resurfaces black smokers
- meets cold sea water
- precipitates valuable mineral deposits
what controls the composition of sea water?
chemical exchange between water and basalts
how is a black smoker created?
sulfur is mixed with oxygenated water
how can a black smoker evolve bacteria communities?
bacteria can utilize sulfur, those bacteria grow, and filter feeders filter out the sulfur, and community evolves
microbes live off of carbon dioxide and sulfur that comes out, generating a beginning of food chain
what is a food chain without sunlight called?
lithotrophic
what are the two ways plates can break up and move?
- plates can separate from each other
- rifting: spreading of ocean breaking up a continent
we create 3km/yr in sea floor spreading, but somehow it must be ridden of, how do we get rid of it?
convergent boundaries (making things collide and break up)
what is the deepest place in the ocean?
ocean trenches
how are ocean trenches created?
- sea floor is spreading
- creates new plate
- plate is shrinking then contracted
- gets dense and it starts sinking 5. plate will bend, bend creates trench
what is an ocean continent convergence that is close to us?
the cascades
what happened to the trenches during the ice age?
so much sediment dumped off the continent that the trenches became filled
what are transformed faults?
numerous short segments where two opposite plates scrape past each other
why must plates break up?
to move around the earth (a sphere)
older rock?
shrinks and sinks
younger rocks?
high and warm
what is the lost city?
life developed in the ridges between old and young crust
what is a volcanic trail?
heat source under the water that is burning through the plate
what is a mantle plume?
jets of hot material rising from deep in the mantle
what is dynamic topography?
how the mantle and crust is pushing up continents
what do mantle plumes lead to?
large igneous provinces
what is believed to happen in 250 million years?
reform supercontinent
if we create a supercontinent in the future, what would happen?
landmass would be so hot that mammals could not exist
