Plate Tectonics
Movement of plates away from each other at divergent boundaries typically shows which of the following average velocities?
5 cm per year
What are two differences between oceanic crust and continental crust?
The continental crust is thicker and less dense than oceanic crust.
Wegener's continental drift hypothesis was weakened because a viable mechanism for moving the continents was lacking.
True
Where would you expect to see alternating bands of rock with different magnetic polarities?
on both sides of the mid-ocean ridge
Oceanic lithosphere contains oceanic crust and the __________.
outermost part of mantle beneath the oceanic crust
In general, how do magnetic objects align relative to Earth's magnetic field?
parallel
Which of the following lithospheric plates is not included among the seven largest?
the Philippine plate
What was Panthalassa?
the single ocean that existed after the Pangaean supercontinent formed
4. During extension, the lithosphere ______.
thins
Which plate boundary is NOT associated with volcanic eruptions?
transform
How are Earth's geographic and magnetic axes oriented relative to each other?
Earth's geographic and magnetic axes are oriented at a slight angle to each other.
Which of the following is an example of a divergent plate boundary?
East Pacific Rise, mid-Atlantic ridge, East African Rift
What was the Tethys Sea?
a piece of the Panthalassa Ocean that existed after the Pangaean supercontinent formed
On average, how long do periods of reverse and normal polarity last?
about 500,000 years
Which of the following statements describes the view held by most geologists about the continents and ocean basins prior to the 1960s?
The ocean basins and continents are geologically old features with a fixed geographic position.
Where do magnetic field lines exit the Earth today?
at the South Pole
What caused the formation of the Himalayas?
the collision of India with Asia
What is the relationship between the mantle and the asthenosphere?
All of the asthenosphere is contained within a larger layer called the mantle.
Which supercontinent contained Africa and South America?
Gondwanaland
Which of the following is a feature of a divergent plate boundary?
an oceanic ridge, a rift valley
Which type of plate boundary is most closely associated with the formation of new ocean floor?
divergent
New oceanic crust and lithosphere are formed at ________.
divergent boundaries by submarine eruptions and intrusions of basaltic magma
What are the three types of plate boundaries?
divergent, convergent, and transform
How often does the Earth's magnetic field switch polarity?
every 100,000 to several million years
Which of the following processes can be observed at the margins of lithospheric plates?
faulting, earthquakes, volcanoes, mountain building
Which geologic features are associated with divergent boundaries?
mid-ocean ridges and continental rift valleys
A ___________ separates the basin from the adjacent uplifted mountains.
normal fault
Earth's magnetic field is similar to which of the following?
the magnetic field of a bar magnet
Where would the north end of a magnet point during a time of reverse polarity?
toward the magnetic south pole
Which of the following statements best describes Wegener's idea of continental drift?
Continents were formerly in different positions on the Earth and have shifted to their present locations over time.
Which tectonic boundary results when two tectonic plates pull apart from each other?
Divergent boundaries
___________ is igneous activity that occurs __________ plate margins.
Intraplate volcanism; away from
What were the names of the two smaller super continents that formed when Pangaea broke apart?
Laurasia and Gondwanaland
How is the thickness of the lithosphere going to change as it moves away from a divergent plate boundary?
Lithosphere will thicken as more mantle is added.
Which of the following statements about tectonic plates is true?
Most tectonic plates contain both oceanic and continental lithosphere.
Which of the following statements about divergent boundaries is true?
New ocean crust is created at a divergent boundary.
Crustal rifting is currently occurring in East Africa. Which of the following features would you expect to find there?
Normal Faults Long, wide valley Lava flows
Which of the following regions was not part of the large Southern Hemisphere continent of Gondwana?
North America
Decompression melting occurs when the ________ upwells.
asthenosphere
Where are tectonic plates located?
at Earth's surface
A ________ is another term for a basin formed by crustal extension.
graben
Which phenomenon can explain the presence of volcanoes in the middle of the Pacific Ocean?
hot spots
What does evidence from ocean drilling for sediment cores support?
seafloor spreading
What surface feature provides evidence for the location of hot spots?
volcanoes within tectonic plates
When will a hot spot volcano become extinct?
when the volcano is carried away from the hot spot by the tectonic plate
Which part of the Earth is responsible for generating the planet's magnetic field?
Core
What is the relationship between the crust and lithosphere?
The crust is part of the lithosphere.
What was Pangaea?
a supercontinent that began to break apart about 200 million years ago
Which of the following is evidence of continental drift?
Glossopteris fossils found on Antarctica and Australia, coal deposits in North America, matching rock units found in Brazil and Africa
How is information about magnetic fields recorded in rocks?
Iron particles in magnetically susceptible minerals within basaltic lava align with the magnetic field of the Earth while the lava is still liquid and then freeze in position when the lava solidifies.
What is the main material being subducted at an ocean-continent convergent boundary?
Oceanic lithosphere
How were scientists able to determine the date of the magnetic reversals during seafloor spreading?
Small marine fossils in deep-sea sediments give the age of the portions of the seafloor
What is the relationship between the mantle and the lithosphere?
Some of the mantle is contained within a smaller layer called the lithosphere.
What evidence supports that the glaciers on the southern continents were once part of a single, massive ice sheet?
Striations
What would happen to Earth if ocean floor were created at divergent boundaries at a faster rate than it is destroyed at convergent boundaries?
The Earth would increase in volume.
What was the first evidence that led early researchers to suspect that Earth's continents were once connected?
The coastlines of the continents, especially South America and Africa, fit together like a jigsaw puzzle.
At a divergent boundary, what is the relative motion of the plates on each side of the boundary?
The plates move away from each other.
When moving away from a divergent boundary in either direction, which of the following statements is true?
The rocks increase in age.
During the breakup of Pangaea, volcanic island arc systems may have formed that no longer exist. What likely happened to these arcs?
They may have been accreted onto continents after their formation.
Divergent boundaries are not one, smooth ridge of separation. Instead, they are broken into a series of segments, with different segments of fault offset from others. What features allow for the offset of divergent boundaries?
Transform faults
What is the relationship between continent edges and plate boundaries?
Very few plate boundaries follow the edges of continents.
Late Paleozoic sedimentary rocks often contain extensive coal seams that were used to support the existence of Pangaea. What would the climate have been at that time and at the location where the coal deposits were formed, and what would it indicate about the continent's past latitude?
Warm, humid climate near the Equator
Which of the following describes why most Earth scientists objected to Wegener's continental drift hypothesis?
Wegener's theory failed to demonstrate a mechanism by which continents could move through ocean crust.
Where is the youngest ocean floor found?
along the crest of mid-ocean ridges
Which of the following techniques can be used to recreate the configuration of supercontinents that existed before Pangaea?
apparently wandering polar paths
Which type of plate boundary is most closely associated with uplifting continental regions and mountain building?
convergent boundaries
Complete this statement: Divergence is to moving away as convergence is to _______.
moving toward
Would be found at a divergent boundary
normal faults, volcanoes producing mafic lavas
Choose the option that does not fit the pattern. fossil evidence paleomagnetism fit of the continents paleoclimate
paleomagnetism
Earth's lithospheric plates are composed of crust and which of the following layers?
the outermost portion of the mantle
How are normal polarity and reverse polarity of Earth's magnetic field different?
A compass points toward the North Pole during normal polarity and to the South Pole during reverse polarity.
In general, what is our best evidence that the orientation of Earth's magnetic field has changed over time?
A record of Earth's magnetic field is recorded in oceanic rocks, which show a clear pattern of changes in Earth's magnetic polarity.
What is the relationship between the crust and the lithosphere?
All of the crust is contained within a larger layer called the lithosphere.
Which of the following mountain ranges are examples of continental arcs?
Andes and Cascades
Which of the following is a layer of the Earth that is classified NOT by composition, but by physical properties?
Asthenosphere
In studies of rock obtained from ocean basins all over Earth, the oldest ages obtained are approximately 200 million years before the present. Why have no older oceanic rocks been discovered?
Due to tectonic activity, rocks on the ocean floor are continually recycled.
Which of the following statements about Earth's magnetic field is most accurate?
Earth's magnetic field switches polarity at irregular time intervals.
Which of the following statements about earthquakes with magnitude greater than 4.0 is most accurate?
Earthquakes with magnitude greater than 4.0 occur in a pattern than correlates closely with plate boundaries.
Earth's radius and surface area are slowly increasing to accommodate the new oceanic crust being formed at mid-ocean ridges.
False
Hawaii is the oldest island of the Hawaiian Island chain.
False
How was the fossil record of ancient life used to support Wegener's hypothesis about Pangaea?
Fossils of identical organisms were found on several continents, indicating the continents were once joined.
Since the breakup of Pangaea approximately 165 million years ago, a new supercontinent cycle has begun with the collision of which of the following continents?
India and Asia
When matching up once-joined continents such as South America and Africa, the coastlines do not fit together as nicely as the continental shelves. Why might this be the case?
The continental shelves are the edges of the continent. The shoreline simply shows where the sea level is in relation to topography.
Which of the following statements accurately describes the difference between the lithosphere and the asthenosphere?
The lithosphere is a strong outer layer of Earth that sits atop the warmer and weaker asthenosphere.
The oldest rocks on the seafloor are much younger than the oldest rocks on the continents.
True
Currently the Juan de Fuca plate is interacting with the North American plate where inland volcanoes and deep focus earthquakes are occurring. What type of plate boundary is this?
a convergent plate boundary
What is a volcanic arc?
a row of volcanoes that forms on the overriding plate near a subduction zone
What surface feature would you expect to form if both a hot spot and a tectonic plate are stationary?
a single volcano
What geologic process initiated the breakup of Pangaea approximately 165 million years ago?
continental rifting
What type of plate boundary is the oldest crust on Earth near?
convergent
Plates move apart at __________ boundaries, move together at __________ boundaries, and move side-by-side at __________ boundaries.
divergent/convergent/transform
Which of the following energy sources is thought to drive the lateral motions of Earth's lithospheric plates?
export of heat from deep in the mantle to the top of the asthenosphere
Continental rifts are formed by _________ forces.
extensional
Evidence supporting the theory of plate tectonics
hot spots paleomagnetism ocean floor drilling
Which geologic features are associated with convergent boundaries?
ocean trenches and volcanoes
________ was never proposed as evidence supporting the existence of Pangaea.
Islands of Precambrian rocks along the Mid-Atlantic Ridge