ch2 geol

Oceanic crust

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

The Earth's magnetic field is created by

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

Modern plate tectonic theory was developed in what decade?

1960s

Plate movement is influenced by each of the following EXCEPT

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

According to current plate tectonics theory, Choose one: A. plates are composed of the crust and the uppermost part of the mantle. B. plates move at speeds of a few meters per year. C. plates move around by convection in the lithosphere. D. a continental plate will subduct under an oceanic plate when the two converge.

A. plates are composed of the crust and the uppermost part of the mantle.

Identify the true statement. Choose one: A. Plates may consist of both ocean floor and continental crust, but never just oceanic or continental crust. B. Plates shift the continents around as they move, so the Earth's surface is constantly changing. C. The contacts between plates are called passive margins. D. There are 120 major tectonic plates.

B. Plates shift the continents around as they move, so the Earth's surface is constantly changing.

Magnetic anomalies are

C. places where the magnetic field strength is either greater or less than the expected strength.

Identify the true statement. Choose one: A. As the seafloor spreads, the lithosphere rises to fill the space between plates. B. Some magma generated during seafloor spreading spills out onto the surface to produce a new layer of seafloor called gabbro. C. The oldest seafloor can be found along a mid-ocean ridge axis. D. Some magma generated during seafloor spreading erupts from submarine volcanoes to form basalt.

D. Some magma generated during seafloor spreading erupts from submarine volcanoes to form basalt.

Identify statements true of Pangaea. Choose one or more: A. Rates of seafloor spreading in the Atlantic Ocean are compatible with what is known about the breakup of Pangaea. B. Pangaea consisted of all of the Earth's continents pushed together with the exception of Antarctica. C. The regional-scale folds visible in the Appalachian Mountains are remnants of Pangaea's formation. D. Pangaea was one of several supercontinents that have formed and broken up during Earth's history.

Rates of seafloor spreading in the Atlantic Ocean are compatible with what is known about the breakup of Pangaea. The regional-scale folds visible in the Appalachian Mountains are remnants of Pangaea's formation. Pangaea was one of several supercontinents that have formed and broken up during Earth's history

Seafloor spreading is driven by volcanic activity that occurs

along mid-ocean ridges.

Wegener's theory of continental drift took decades to be accepted

because Wegener couldn't explain how continents moved.

The rate of plate motion

can be expressed as relative plate velocity, which describes movement of one plate in relation to another plate.

The center of a mid-ocean ridge is where

new oceanic lithosphere is created.

During World War II, the military imaged the seafloor by sending pulses of sound waves down through the water and measuring the time it took for the sound to bounce off the seafloor and return to the receiver. This method is called

sonar.

Oceanic lithosphere Choose one: A. gets older and thinner as it gets farther from the ridge axis. B. attains its maximum thickness when it is about 800 million years old. C. that is 10 million years old is cool enough to be denser than the asthenosphere, so it can sink down into or through the asthenosphere. D. gets warmer as it gets farther from the ridge axis.

that is 10 million years old is cool enough to be denser than the asthenosphere, so it can sink down into or through the asthenosphere.

The global occurrence of earthquakes reveals that

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

Of the choices below, select the one that accurately pairs the feature with the type of plate boundary at which it occurs. Choose one: A. Trenches occur at subduction zones. B. Accretionary prisms occur at divergent boundaries. C. Black smokers occur at consuming boundaries. D. Volcanic arcs occur at transform boundaries.

A. Trenches occur at subduction zones.

Which of the following variables could influence the width of marine magnetic anomalies on the floor of the ocean? A. rate at which the plates are moving away from the mid-ocean ridge B. duration of the magnetic polarity event C. frequency of sunspot activity D. latitude at which the anomaly formed E. strength of the magnetic field

A. rate at which the plates are moving away from the mid-ocean ridge B. duration of the magnetic polarity event

Accretionary prisms form due to what process?

D. subduction

Which of the following statements about lithosphere and asthenosphere is true? Choose one: A. Lithosphere and asthenosphere have the same physical properties; they are both rigid. B. Lithosphere is more mafic than asthenosphere. C. Asthenosphere is defined as mantle material that is cooler than 1,280°C, whereas lithosphere is warmer than 1,280°C. D. Lithosphere consists of the crust and the upper mantle and behaves like a rigid layer that breaks or bends rather than flowing like the asthenosphere.

Lithosphere consists of the crust and the upper mantle and behaves like a rigid layer that breaks or bends rather than flowing like the asthenosphere.

Identify the true statement. Choose one: A. Positive magnetic anomalies occur where seafloor basalt has the same polarity as Earth's present-day magnetic field. B. All polarity chrons are the same length of time; they differ only in the magnetic strengths they represent. C. The width of each rock stripe is a measure of how long the polar direction took to change. D. The series of rock stripes perpendicular to and bilaterally symmetric across the mid-ocean ridge records the sequence of the Earth's magnetic reversals over time.

Positive magnetic anomalies occur where seafloor basalt has the same polarity as Earth's present-day magnetic field.

The Himalayas are growing because

a continental plate is colliding with another continental plate there.

A global map of seismicity shows seismic trends indicating the location of

plate boundaries.