Chapter 17 Study Guide

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

False; ocean ridges

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: Rock samples taken near ocean ridges are ​older​ than rock samples taken near deep-sea trenches.

False; younger

Use each of the terms below just once to complete the passage. isochron magnetic field normal polarity older reversed polarity younger Earth's ​(17)​ ______________________ has changed over time. A field with the same orientation as today's field is said to have ​(18)​ ______________________. A field that is opposite the present field has ​(19)​ ______________________. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ ______________________ maps, which have shown that the ocean floor is (21)​ ______________________ near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(17) magnetic field

Use each of the terms below just once to complete the passage. isochron normal polarity older reversed polarity younger Earth's ​(17)​ magnetic field has changed over time. A field with the same orientation as today's field is said to have ​(18)​ ______________________. A field that is opposite the present field has ​(19)​ ______________________. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ ______________________ maps, which have shown that the ocean floor is (21)​ ______________________ near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(18) normal polarity

Use each of the terms below just once to complete the passage. isochron older reversed polarity younger Earth's ​(17)​ magnetic field has changed over time. A field with the same orientation as today's field is said to have ​(18)​ normal polarity. A field that is opposite the present field has ​(19)​ ______________________. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ ______________________ maps, which have shown that the ocean floor is (21)​ ______________________ near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(19) reversed polarity

Use each of the terms below just once to complete the passage. isochron older younger Earth's ​(17)​ magnetic field has changed over time. A field with the same orientation as today's field is said to have ​(18)​ normal polarity. A field that is opposite the present field has ​(19)​ reversed polarity. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ ______________________ maps, which have shown that the ocean floor is (21)​ ______________________ near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(20) isochron

Use each of the terms below just once to complete the passage. older younger Earth's ​(17)​ magnetic field has changed over time. A field with the same orientation as today's field is said to have ​(18)​ normal polarity. A field that is opposite the present field has ​(19)​ reversed polarity. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ isochron maps, which have shown that the ocean floor is (21)​ ______________________ near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(21) younger

Use each of the terms below just once to complete the passage. older Earth's ​(17)​ magnetic field has changed over time. A field with the same orientation as today's field is said to have ​(18)​ normal polarity. A field that is opposite the present field has ​(19)​ reversed polarity. Magnetometers have been used to measure the ocean floor's magnetic field. Magnetic data of the ocean floor has been used to generate ​(20)​ isochron maps, which have shown that the ocean floor is (21)​ younger near ocean ridges and ​(22)​ ______________________ near deep-sea trenches.

(22) older

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, and becomes more dense

The statements below describe the steps involved in the process of seafloor spreading. Number these steps in the order in which they occur. __________ Magma fills the gap that is created. __________ Magma hardens to form new ocean crust. __________ Magma is forced upward toward the crust.

2 Magma fills the gap that is created. 3 Magma hardens to form new ocean crust. 1 Magma is forced upward toward the crust.

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

False; increases

Compare and contrast ridge push and slab pull.

As oceanic crust cools and moves away from a divergent boundary, it becomes denser and sinks compared to the newer, less-dense oceanic crust. As the older portion of the seafloor sinks, the weight of the uplifted ridge is thought to push the oceanic plate toward the trench formed at the subduction zone in a process called ridge push. In slab pull, the weight of the relatively cool, dense subducting plate pulls the trailing slab into the subduction zone much like a tablecloth slipping off the table can pull articles off with it. Slab pull is thought to be at least twice as important as ridge push in moving and oceanic plate away from an ocean ridge. It is likely that the combination of mechanisms such as these are involved in plate motions at subduction zones.

Explain the process of convection.

Convection is the transfer of thermal energy by the movement of heated material from one place to another.

True or False: The oldest ocean floor rocks are about ​3.8 billion​ years old.

False; 180 million

True or False: An isochron​ is a change in Earth's magnetic field.

False; Magnetic reversal

True or False: Deep-sea trenches​ are vast, underwater mountain chains.

False; Ocean ridges

Describe the formation of convection currents in the mantle.

In the convection currents of the mantle, cooler mantle material is denser than hot mantle material. The mantle that has cooled at the base of tectonic plates slowly sinks down toward the center of Earth. Heated mantle material is then displaced, and like the wax warmed in a lava lamp, it rises. Convection currents in the mantle are sustained by this rise and fall of material which results in a transfer of energy between Earth's hot interior and cooler exterior.

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

The rising material in the convection current spreads out as it reaches the upper mantle and causes both upward and sideways forces. These forces lift and split the lithosphere at divergent plate boundaries. As the plates separate, material rising from the mantle supplies the magma that hardens to form new ocean crust. The downward part of a convection current occurs where are sinking force pulls tectonic plates downward at convergent boundaries.

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: Sonar​ uses sound waves to measure water depth.

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

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 a. divergent boundary. b. convergent boundary. c. subduction zone. d. transform boundary.

a. divergent boundary.

For each item in Column A, write the letter of the matching item in Column B. Column A ______ This type of line connects points on a map that have the same age Column B a. isochron b. iron (already picked) c. geomagnetic time scale (already picked) d. new ocean crust e. magnetometer (already picked)

a. isochron

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 fossils had once been joined. c. Earth's continents were never joined. d. Glossopteris​ grew only in the tropics.

b. continental rocks containing these fossils had once been joined.

For each item in Column A, write the letter of the matching item in Column B. Column A ______ Minerals containing this act like small compass needles and record the orientation of Earth's magnetic field at the time of their formation Column B a. isochron b. iron c. geomagnetic time scale d. new ocean crust e. magnetometer (already picked)

b. iron

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 formations.

b. magnetic field data.

For each item in Column A, write the letter of the matching item in Column B. Column A ______ Each cycle of spreading and magma intrusion along an ocean ridge results in the formation of this Column B a. isochron (already picked) b. iron (already picked) c. geomagnetic time scale (already picked) d. new ocean crust e. magnetometer (already picked)

d. new ocean crust

For each item in Column A, write the letter of the matching item in Column B. Column A ______ Was constructed from data gathered from continental basalt flows Column B a. isochron b. iron (already picked) c. geomagnetic time scale d. new ocean crust e. magnetometer (already picked)

c. geomagnetic time scale

Coal beds in Antarctica indicated to Wegener that this continent was a. always cold. b. inhabited by penguins. c. once located closer to the equator. d. once beneath the ocean.

c. once located closer to 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

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 form. 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.

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.

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 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.

Places where tectonic plates move apart are called a. convergent boundaries. b. transform boundaries. c. subduction zones. d. divergent boundaries.

d. divergent boundaries.

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.

d. earthquakes and floods.

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.

d. once lived in Earth's oceans.

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 the 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 earthquakes c. long faults d. volcanoes

d. volcanoes

For each item in Column A, write the letter of the matching item in Column B. Column A ______ Device that can detect small changes in magnetic fields Column B a. isochron b. iron c. geomagnetic time scale d. new ocean crust e. magnetometer

e. magnetometer