GEO102 Part2

The chain of volcanoes along the west coast of South America (the Andes Mountains) exists because

an oceanic plate is subducting under the western edge of the South American Plate.

Choose the FALSE statement. Magnetic anomalies are A. termed normal if the atomic dipoles match Earth's current magnetic field and point from north to south. B. found only on the seafloor. C. measured with an instrument called a magnetometer. D. places where the magnetic field strength is either greater or less than the expected strength.

B. found only on the seafloor.

Identify the FALSE statement. According to the mantle plume model, hot-spot plumes A. stream upward slowly because their hot rock is less dense than the overlying rock. B. are thought to originate at the crust-mantle boundary. C. produce volcanoes that do not always coincide with a plate boundary. D. can occur beneath ocean plates as well as continental plates.

B. are thought to originate at the crust-mantle boundary.

Identify the FALSE statement. Oceanic lithosphere A. gets older and thicker as it gets farther from the ridge axis. B. attains its maximum thickness when it is about 800 million years old. C. effectively does not exist beneath the mid-ocean ridge axis. D. gets cooler as it gets farther from the ridge axis.

B. attains its maximum thickness when it is about 800 million years old.

The global occurrence of earthquakes reveals that

they usually occur on the boundaries of plates or at hot spots.

The center of a mid-ocean ridge is where

new oceanic lithosphere is being created.

Accretionary prisms form due to what process?

subduction

Identify the FALSE statement. A subducting (or downgoing) plate A. can be either continental or oceanic lithosphere. B. can be charted by noting its Wadati-Benioff zone. C. has a volcanic arc associated with it. D. has a trench along its seaward edge.

A. can be either continental or oceanic lithosphere.

Identify the FALSE statement. A. Positive magnetic anomalies occur over areas of seafloor when the poles of Earth's magnetic field and the paleopoles preserved in the seafloor basalt agree; negative anomalies occur when they are opposite each other. B. The series of rock stripes parallel to and bilaterally symmetrical across the mid-ocean ridge record the sequence of Earth's magnetic reversals over time. C. The width of each rock stripe is a measure of how long the polar direction remained constant. D. All polarity chrons are the same length of time; they differ only in the magnetic strengths they represent.

D. All polarity chrons are the same length of time; they differ only in the magnetic strengths they represent.

Plate tectonics theory was widely accepted by scientists in what decade?

1960s

Radiometric dating of a magnetic anomaly stripe of rock that is 225 km away from the mid-ocean ridge axis gives an age of 4.5 million years. Assuming a constant rate, seafloor spreading in this area occurs at a rate of

5cm per year

The chain of Hawaiian Islands extends northwest across the Pacific as shown in the figure. The island of Hawaii is the youngest, and the islands get progressively older to the northwest. How does plate tectonic theory explain this?

A hot spot is currently situated under Hawaii and the Pacific Plate is moving across it in a northwesterly direction.

Identify the FALSE statement. A. Some magma generated during seafloor spreading erupts from submarine volcanoes. B. Some magma generated during seafloor spreading spills out to produce a new layer of seafloor called gabbro. C. Observers in research submersibles have seen submarine volcanoes. D. As the seafloor spreads, the asthenosphere rises, melts to become magma, and fills the space between plates.

B. Some magma generated during seafloor spreading spills out to produce a new layer of seafloor called gabbro.

Earth's magnetic field is created by

flow of liquid iron in Earth's molten outer core.

The diagram shows how the tilt of a magnetic needle changes with latitude. What part of the Earth's magnetic field does this illustrate?

inclination

Ocean crust

is covered by a thin blanket of sediment that thickens away from the ridge axis.

Asthenosphere

is warm enough to flow slowly.

Identify the FALSE statement. The rate of plate motion A. can be expressed as relative plate velocity, which describes movement of one plate in relation to another plate. B. can range from 100 to 150 cm per year. C. can be expressed as absolute plate velocity, which describes movement of a single plate relative to a fixed point. D. can be determined to within millimeters by using the global positioning system (GPS).

B. can range from 100 to 150 cm per year.

Which of the following statements is NOT true about the ocean floor? A. Oceanic crust is quite different from continental crust. B. The heat flow through it is greatest at the mid-ocean ridges. C. It is covered by a layer of sediment composed of clay and plankton shells. D. Oceanic crust contains granite and metamorphic rocks.

D. Oceanic crust contains granite and metamorphic rocks.

Identify the FALSE statement. A. Plates shift the continents around as they move, so Earth's surface is constantly changing. B. Plates may consist of all ocean floor or both ocean floor and continental crust. C. There are 12 major plates, and several microplates. D. The contacts between plates are called passive margins.

D. The contacts between plates are called passive margins.

Plate tectonics theory took decades to be accepted because

Wegener couldn't explain how continents moved

The Himalayas are growing because

a continental plate is colliding with another continental plate there.

Identify the FALSE statement. A. A spreading boundary must be in the middle of the ocean basin where it is located. B. Plate boundaries where subduction occurs are also called consuming boundaries. C. Seafloor spreading behind a volcanic island arc creates a small ocean basin called a back-arc basin or marginal sea. D. An accretionary prism is a wedge-shaped mass of sediment scraped off a subducting plate as it slides under the overriding plate.

A. A spreading boundary must be in the middle of the ocean basin where it is located.

Identify the FALSE statement. Plate movement is influenced by A. mantle convection, which creates shear at the base of plates. B. ridge push, in which the elevated rocks at the ridge axis push on rocks farther from the ridge. C. mantle plumes, which are created when hot rock rises up from the deep mantle and creates melting at the base of the lithosphere. D. slab pull, in which the downgoing oceanic plate exerts a pull on the rest of the plate.

C. mantle plumes, which are created when hot rock rises up from the deep mantle and creates melting at the base of the lithosphere.

Which of the following was NOT a line of evidence used by Wegener to develop this theory that continents drift? A. matching mountain chains on continents currently separated by oceans B. the distribution of fossil species C. the presence of earthquakes in seismic belts along trenches, ridges, and fracture zones D. the location of ancient till deposits and striations that indicated glacial movement toward the interior of continents

C. the presence of earthquakes in seismic belts along trenches, ridges, and fracture zones

Identify the TRUE statement associated with this diagram. A. Apparent polar-wander paths prove that Earth's magnetic poles wandered up to 90 degrees from their current position through geologic time. B. The apparent polar-wander path of Africa is the same as that of Europe C. The apparent polar-wander paths of North America and Europe are similar enough to indicate that these continents did not move with respect to each other. D. Apparent polar-wander paths were created by measuring the paleomagnetism in rocks of different ages from the same location.

D. Apparent polar-wander paths were created by measuring the paleomagnetism in rocks of different ages from the same location.