Plate Tectonics Flashcards
What was Alfred Wegner’s theory called?
Theory of continental drift.
Does fossil evidence support or contradict
the hypothesis that continents drifted?
Explain.
Yes, due to the fact that many fossils have been found on two of todays seperate continents.
Does evidence from stratigraphy support
or contradict the hypothesis that
continents drifted? Give examples.
Yes, due to remarkably similar sequences found in South America and Africa. This is strong evidence of their closeness.
What are striations, and what do they
indicate about the movement of glaciers?
How does geologic evidence of striations
bear on continental drift?
Striations are scratches on a rock left by passage of glacier. They confirm glacier presence and tell direction of ice movement.
Does evidence from glaciers support or
contradict the hypothesis that continents
drifted? Give examples.
Supports. The examples are based upon antarctica being in the middle and the glaciers moving outwards.
What did evidence from geological
structures, such as mountain ranges, “say” about the hypothesis that continentsdrifted? Give examples.
It said that this theory is accurately presented because of the belts that are aligned from one continent to another.
Why did Wegner’s contemporary
colleagues reject his theory? Explain.
Wegners theory did not explain WHAT moved the conitinents. There was no known force on Earth that could cause continents to drift.
What was Harry Hess’s model for the
mid-ocean ridge? (Hint: describe the structure of the ridge, and explain what happens there).
Sea floor spreading. Caused by the sea floor being driven by forces deep inside the earth.
What is mantle convection and why does
it happen? Explain.
The motion of the mantle that causes lithosphere sea floor spreading. It is caused by a difference in temperature between the mantle and the outside of the earth.
If Harry Hess’s theory of sea floor
spreading was true, then how would the
location of igneous rocks that formed at
an ocean ridge change during the
passage of millions of years after their
formation? Explain.
The rocks are pushed further away from the middle of the mountain range so over the course of millions of years the location would be much further away.
Calculation: If some rocks formed at the
mid-ocean ridge 10 million years ago,
then how far away from the ridge (in km,
meters, and cm) would they be now,
given a rate of sea floor movement of 2
cm/yr? (Fully worked out solution is on
the next page – try this yourself first, don’t
cheat yourself out of a learning exercise!).
20 million centimeters
200,000 meters
200 kilometers
What was Wegner’s unsolved problem
about the movement of continents? How
did Harry Hess’s theory solve Wegner’s
problem?
His unsolved problem was HOW the continents moved.
Hess solved this problem with sea floor spreading theory.
For what discovery is J. Tuzo Wilson
famous?
Disvovered “hotspots”
What are oceanic trench systems? Where
are the major trenches found?
Narrow topographic depressions on the seafloor.
The major trenches are found : 1. Aleutian trench, south of alaska. 2. the south american trench, west of the continent. 3. Mariana trench, kermadec- tonga trench off coast of Australia.
All are located close to the ring of fire.
What discovery was made at the
Kermadec-Tonga trench, and why was it
important?
Subduction zones, they were the last major leg of the theory of tectonics.
What are “plates” in plate tectonic theory?
“Plates” of plate tectonics are the sections of the lithosphere (either continent, ocean, or a combination of the two) into which the outermost layer of the earth is divided.
What forces move the plates? Where do
these forces act?
Gravity-slide= push from ridge (closer to the surace)
Convection or frictional drag (in the middle)
Gravity-slide=pull in subduction zone (towards the bottom)
Be able to identify by name the plates
(discussed in class) on a world map.
do it.
What are the names of the three or four
largest plates?
Pacific plate
Eurasian plate
Antarctic plate
North American plate
What are the three possible types of
tectonic boundaries between plates?
Describe the relative movement of the
lithosphere on opposite sides of each of
these boundaries.
spreading centers (they move away from each other)
subduction zones ()
transform faults ()
Which named plates are made entirely of
oceanic crust?
