Continental Drift, Tectonic Plates, and Earthquakes Flashcards
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
_________ and _________ are common at convergent boundaries
- volcanos
- earthquakes
The destruction or recycling of the Earth’s crust takes place at _______ __________
convergent boundaries
TRUE or FALSE: Lighter material rises above heavier material
TRUE
What type of crust is denser, oceanic or continental?
oceanic crust is denser
Continental crust is made with _______ type rocks while oceanic crust is made with _______
- granite
- basalt (dark colored rocks)
If the subducting oceanic plate subducts beneath an adjacent
oceanic plate, an _______ ______ is formed
island arc
if the subducting oceanic plate subducts beneath a continental crust, then a similar belt of ______ will be generated on the continent. These are called ______ ______.
- volcanoes
- volcanic arcs
When it comes to transform boundaries, horizontal movement means:
no new creation of crust nor destruction of crust
The movement of transform boundaries is continuous but sometimes, the plates stick due to _______ and then eventually get free of each other resulting in __________.
- friction
- earthquakes
Where do 95% of earthquakes occur?
near a new plate boundary
We can know where an earthquake is likely to occur, but not ______.
when
Approximately ___% of the most powerful volcanic eruptions and about ___% of the world’s largest earthquakes have occurred along the Ring of Fire.
- 90%
- 81%
What is the intensity of an earthquake determined by?
It is determined by the amount of of damage caused by how much the ground shakes
The study of earthquakes and seismic waves is called _________
Seismology
An instrument that records earthquake waves is called a _________
seismograph
What are the three types of seismic waves that earthquakes generate?
- p (primary) waves
- s (secondary) waves
- surface waves
waves that travel through the interior of the earth are called ______ ______.
body waves
primary waves
- longitudinal waves
- fastest seismic waves
- first wave to be recorded
secondary waves
- transverse waves that travel only through solid materials
- slower than p wave but faster than surface waves
Particles will vibrate/move about their ______ position
but particles are not ______ with the wave
- fixed
- carried
Surface waves
- waves that travel through the surface of the earth
- Two types:
➢ Love Waves – moves like S-waves but the shaking
is side to side. This is particularly damaging to
buildings
➢ Rayleigh Waves – roll over and over in a backward
tumbling motion
_________ is related to the amount of seismic energy released
during an earthquake.
magnitude
The scale used to measure the magnitude and intensity of
an earthquake is called the _________ ______. It assigns a single number to an earthquake based on the ________ of the earthquake waves.
- Richter scale
- amplitude
The Richter scale is a _______ scale, meaning that a difference of 1.0 in the Richter scale is equivalent to a __ fold increase
- logarithmic
- 10
What are the two things that the Richter scale measures?
- Intensity (amount of ground shaking that occurs)
- amount of energy released
What is the equation for calculating the energy released in the Richter scale?
Energy released (E) = 10 [11.8 + (1.5 X R)]
- R represents the magnitude of the earthquake
The energy units in the Richter scale are called ______
ergs
1 erg = joules
10-7
TRUE or FALSE: When it comes to earthquakes, magnitude is strongly correlated to destruction
FALSE: Magnitude is NOT correlated to destruction
What are the five factors that might affect the amount of destruction caused by an earthquake?
- Depth and distance to the epicenter
- Human population density near the epicenter
- Amount and strength of infrastructure
- duration of shaking
- awareness/education
An earthquake that hits in a __________ area is more likely to do damage than one that hits an _________ area
- populated
- unpopulated
location on the surface directly above the
focus (The place where the earthquake’s intensity is
greatest) is called the ________
epicenter
The place from where energy from an earthquake is released is called the _____
focus
How is an earthquake located?
Based on the time delay (between P and S wave), we can estimate the distance (d) of the epicenter of the earthquake from the measuring station
Between the P wave and S wave, which wave arrives to the measuring station first?
P wave
When it comes to the distance equation, the _______ symbol is used to represent a change in time
delta
how does distance measurement help
us determine the exact location of an
earthquake?
When we have distance measurements from three different
locations:
* We use the process of triangulation to pinpoint the epicenter
* Triangulation works by drawing circles at the appropriate
distance from the monitoring station
* The location of the epicenter is where the three circles
overlap
