Chapter 17 Study Guide - Plate Tectonics

True or False? The theory of *continental drift* states that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches.

False, seafloor spreading

True or False? *Deep-sea trenches* are vast, underwater mountain chains.

False, ocean ridges

True or False? Rock samples taken near ocean ridges are *older* than rock samples taken near deep-sea trenches.

False, younger

What can happen when two oceanic plates converge and one is subducted into the mantle? A. Magma erupts and forms an arc of islands B. The colliding plate edges become crumpled to form a mountain range. C. The lithosphere splits to create a divergent plate boundary on land. D. A continent splits to form a new ocean basin.

A. Magma erupts and forms an arc of islands

Places where tectonic plates come together are called... A. convergent boundaries B. divergent boundaries C. transform boundaries D. rift valleys

A. convergent boundaries

The Mid-Atlantic Ridge is an example of... A. divergent boundary B. convergent boundary C. subduction zone D. transform boundary

A. divergent boundary

Fossil evidence that supported Wegener's idea of continental drift included... A. land-dwelling animals B. ocean plants C. ocean mammals D. tropical flowers

A. land-dwelling animals

Where are most divergent boundaries found... A. on the seafloor B. on continents C. along coastlines D. at subduction zones

A. on the seafloor

At which tectonic plate boundary do plates slide horizontally past each other? A. transform boundary B. divergent boundary C. continental-continental boundary D. oceanic-oceanic boundary

A. transform boundary

What happens along a divergent boundary on the seafloor? A. Continental mountain ranges form B. New ocean crust forms C. Oceanic plates are subducted into the mantle D. Ocean basins become smaller

B. New ocean crust forms

Which feature is associated with a continental-continental plate boundary? A. a subduction zone B. a mountain range C. a deep-sea trench D. a volcano

B. a mountain range

Which of the following landforms results from divergence of continental crust? A. a mountain range B. a rift valley C. a deep-sea trench D. a long fault

B. a rift valley

Oceanic crust is made mostly of... A. granite B. basalt C. water D. sediments

B. basalt

Tectonic plates interact at places called plate... A. reversals B. boundaries C. regions D. subductions

B. boundaries

Based on observations of fossils of Glossopteris, Wegener concluded that... A. magnetic reversals had occurred in Earth's past B. continental rocks containing these rocks had once been joined C. Earth's continents were never joined D. Glossopteris grew only in the tropics

B. continental rocks containing these rocks had once been joined

To support his hypothesis of continental drift, Alfred Wegener did *NOT* use.... A. ancient climatic evidence B. magnetic field data C. data on ancient reptiles and ferns D. evidence from rock formation

B. magnetic field data

Fossils of aquatic reptiles found in freshwater rocks suggested to Wegener that these reptiles... A. swam the great distances between continents B. probably did not cross the oceans C. ate Glossopteris D. once lived in Earth's oceans

B. probably did not cross the oceans

Compare and contrast ridge push and slab pull.

Both are processes associated with plate movements. Ridge push is a process in which the uplifted ridge is thought to push the oceanic plate toward the subduction zone. Slab pull is a process where by the weight of a subducting plate helps to pull the trailing lithosphere into the subduction zone.

List these steps in the order in which they occur. A. Magma fills the gap that is created. B. Magma hardens to form new ocean crust. C. Magma is forced upward toward the crust.

C, A, B

Based on the glacial deposits he observed, Wegener argued that... A. glaciers formed near the equator B. Earth's axis of rotation had changed in the past C. landmasses drifted away in the South Pole D. Glossopteris could not survive hot weather.

C. landmasses drifted away in the South Pole

Early mapmakers thought continents might have moved based on their observations of... A. magnetism B. rock and fossil evidence C. matching coastlines D. earthquakes and floods

C. matching coastlines

Coal beds in Antarctica indicated to Wegener that this continent was.... A. always cold B. inhabited by penguins C. once located near the equator D. once beneath the ocean

C. once located near the equator

Which of the following features forms when two oceanic plates converge? A. magnetic reversal patterns B. divergent boundaries C. subduction zones D. rift valleys

C. subduction zones

Places where tectonic plates move apart are called... A. convergent boundaries B. transform boundaries C. subduction zones D. divergent boundaries

D. divergent boundaries

Explain the process of convection.

Convection is the transfer of thermal energy by the movement of heated matter. Heating matter causes it to expand and decrease in density. This warmed matter is forced upward as a result of buoyancy. The cooler part of the matter is pulled downward as a result of gravity. This up-and-down flow creates a pattern of motion called a convection current.

Pangaea was an ancient supercontinent made up of... A. South Africa, India, Australia, and South America B. the United States, Greenland, and Europe C. Antarctica, India, and South America D. All of Earth's continents

D. All of Earth's continents

Which of the following best describes what happens when an oceanic plate converges with a continental plate? A. A deep-sea trench and an island arc forms B. Both plates become fractured, and a series of long faults form on the surface C. Both plates crumple and a folded mountain range forms. D. A trench and a mountain range with many volcanoes can form.

D. a trench and a mountain range with many volcanoes can form.

Most scientists at the time rejected Wegener's hypothesis of continental drift because he.... A. had collected little evidence to support his hypothesis B. would not state his hypothesis publicly C. insisted that the Earth's axis of rotation had changed D. couldn't explain how or why the continents moved.

D. couldn't explain how or why the continents moved.

Which theory states that Earth's crust and rigid upper mantle move in different directions and at different rates over Earth's surface? A. ridge push and slab pull B. seafloor spreading C. continental drift D. plate tectonics

D. plate tectonics

Convergent boundaries are classified according to the... A. types of fossils found at the boundaries B. rate at which the plates collide C. compass direction of movement of plates. D. type of crust involved.

D. type of crust involved

Which of the following is NOT associated with transform boundaries? A. deformed and fractured crust B. shallow earthquake C. long faults D. volcanoes

D. volcanoes

Describe the formation of convection currents in the mantle.

Even though it is a solid, the upper mantle can flow like a soft plastic. Convection currents are set in motion by the transfer of energy between Earth's hot interior and cooler exterior. Regions of hot mantle are less dense than areas of cooler mantle and are slowly forced toward the crust. Cooler parts of the mantle sink back toward the core. The convection currents that result are probably set in motion by subducting slabs.

True or False? The oldest ocean floor rocks are about *3.8 billion* years old.

False, 180 million

True or False? As new seafloor is carried away from an ocean ridge, it becomes more dense *heats up, expands, and becomes less dense* than the material beneath it.

False, cools, contracts, becomes more dense

True or False? The thickness of ocean-floor sediments *decreases* with distance from an ocean ridge.

False, increases

True or False? An *isochron* is a change in Earth's magnetic field.

False, magnetic reversal

True or False? The magnetic patterns on either side of a *deep-sea trench* are mirror images of each other.

False, ocean ridge

Explain how the parts of a convection current in the mantle are related to plate motions.

The rising part of a convection current spreads out as it reaches the upper mantle and causes lateral and upward forces. These forces lift and split the lithosphere at a divergent boundary. The downward part of the current occurs where a sinking force pulls plates downward at convergent boundaries.

True or False? *Sonar* uses sound waves to measure water depth.

True

True or False? Earthquake activity and volcanism are common along *ocean ridges*.

True

True or False? Maps made from sonar and magnetometer data led to the discovery of *ocean ridges and deep-sea trenches*.

True

True or False? The study of the magnetic record preserved in Earth's rocks is called *paleomagnetism*.

True

True or False? The theory of seafloor spreading explains that Earth's continents move because they *ride atop ocean crust as it moves away from ocean ridges*.

True

Was constructed from data gathered from continental basalt flows.

geomagnetic time scale

Minerals containing this act like small compass needles and record the orientation of Earth's magnetic field at the time of their formation.

iron

This type of line connects points on a map that have the same age

isochron

Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ______________________ maps, which have shown that the ocean floor is ______________________ near ocean ridges and ______________________ near deep-sea trenches.

isochron, younger, older

Earth's ______________________ has changed over time.

magnetic field

Device that can detect small changes in magnetic fields

magnetometer

Each cycle of spreading and magma intrusion along an ocean ridge results in the formation of this.

new ocean crust

A field with the same orientation as today's field is said to have ______________________.

normal polarity

A field that is opposite the present field has ______________________.

opposite polarity