Continental Drift, Tectonic Plates, and Earthquakes Flashcards
(61 cards)
What was Alfred Wegener’s hypothesis of the continental drift?
he hypothesized that The continents were once joined in a “super-continent” (Pangaea or Pangea) and have since separated and spread apart
What are six pieces of evidence that support Wegener’s hypothesis?
- continents seemed to fit together like a jigsaw puzzle, especially Africa and South America (aka matching continental margins)
- Fossil evidence (Matching Fossils) – nearly
identical land dwelling animals and plants across the oceans - matching rock types
- mountain ranges in comparable age and
structure on different continents - ancient ice sheets near the equator
- location of young mountains along edges of continents
What were the problem’s with Wegener’s hypothesis?
- Still the question of How could the apparently rock-based continents “float” on the oceans like pieces of wood?
- Doesn’t explain what would make the continents drift apart
Why was Wegener’s hypothesis dismissed?
At the time there was no satisfactory explanation for the force that pushes or pulls the massive continents and therefore could not identify the cause of continental drift
During and after WWII ____ ________ were used to map the ocean floor
echo sounders
Scientist Harry Hess used echo sounders to:
survey the ocean floor
When surveying the ocean floor, what did Harry Hess predict?
That the ocean floor would be a “flat plain”
What four things did Hess find when surveying the ocean floor with echo sounders?
- Undersea mountain ranges
- Mid-ocean ridges
- Deep undersea valleys (ocean trenches)
- deep sea volcanoes
What did Harry Hess discover was happening at the mid-ocean ridges?
- Magma was welling up and new crusts were being formed at these locations, moving laterally outwards
- Magnetometer data revealed an alternating “striped” pattern of seafloor rock
- new ocean crust was created at the ridge crest and then spread outwards in both directions
- the pattern of magnetic strips shows that the seafloor is spreading at mid-ocean ridges
After Harry Hess learned that the ocean was not a flat plain, what was his new hypothesis?
He hypothesized that the seafloor spreads apart in a process called “seafloor spreading” (seafloor crust was continually forming at mid-ocean ridges and then moving laterally outwards), providing a mechanism for the movement of the continents
What was the first new piece of evidence to support Wegener’s hypothesis of Continental Drift?
seafloor spreading
What are the four layers of the earth?
- crust
- mantle
- outer core
- inner core
What are the two things that represent changes in the mechanical properties of the earth?
- Lithosphere (earth’s outer shell, tectonic plates)
- Asthenosphere (acts as a lubricant for the tectonic plates to slide over)
Scientists combined the continental drift and seafloor
spreading hypotheses to propose the theory of ____ _______
plate tectonics
The Theory of plate tectonics states:
that earth’s lithosphere is divided into tectonic plates and these plates are in slow and constant motion
Earth’s outer shell (lithosphere) is divided into _____ larger
pieces and some smaller ones, called _______ ________. These plates “_____” on top of an underlying rock layer
called the __________ (rocks are under such
tremendous heat and pressure that they behave like a
_________ _______).
- 8
- tectonic plates
- float
- asthenosphere
- viscous liquid
The continents are _________ on the plates which move, which means:
- embedded
- the whole plate moves, not just the continents
locations where two tectonic plates meet are called _______ _________.
plate boundaries
What are the three types of plate boundaries?
- convergent (where plates meet head-on)
- divergent (where plates pull apart)
- transform (where plates grind past each other)
What is the mechanism of sea floor spreading?
magma (molten rock) rises from the earth’s mantle to the
surface, solidifying to create new sea floor crust
__________ represents the largest portion of the mid-Atlantic ridge exposed above sea level
Iceland
Divergent boundaries are responsible for the formation of _____ ______, which can eventually be filled with ______ and become an _______
- rift valleys
- water
- ocean
Where is the lowest land elevation on earth? How long is it?
the rift valley between the Arabian plate and African plate, aka the dead sea, which is 430m.
Regions where neighboring plates come
together (aka convergent boundaries) usually results in a _________. What does this mean?
- subduction
- one plate descends below the other
