Chapter 17

Hot magma fills the gap that forms at the ridge.

B.

Did everyone believe in Plate Tectonics when it was first introduced? Why or why not?

No, because Wegener could not prove what caused the plates to move Plus he was a meteorologist and not a geologist.

The study of Earth's magnetic record is known as _____.

Paleomagnetism

Earth's continents were once joined as a single landmass called _____.

Pangaea.

A landmass thought to have been comprised of present-day southern continents.

Gondwanaland

The theory of _____ explains how new ocean crust is created at ocean ridges and destroyed in deep-sea trenches.

Seafloor spreading.

Hot magma is forced toward crust along an ocean ridge.

A.

Continental drift was not widely accepted when it was first proposed because ____. A. Wegener couldn't explain why or how the continents moved B. continental landmasses were too big to move slowly over Earth's surface C. magnetic and sonar data proved that Wegener's hypothesis was incorrect D. mantle convection currents weren't in motion at that time.

A. Wegener couldn't explain why or how the continents moved

The magnetic pattern of ocean-floor rocks on one side of an ocean ridge is _____. A. a mirror image of that of the other side B. younger than on the other side C. much different from the magnetic pattern found in rocks on land D. at right angles to the ocean ridge.

A. a mirror image of that of the other side

A narrow, elongated depression in the seafloor is called a(n) _____. A. deep-sea trench B. oceanic crust C. ocean ridge D. ocean floor sediment

A. deep-sea trench

Features found at divergent boundaries include _____. A. ocean ridges B. deep-sea trenches C. crumpled mountains D. island arc volcanoes

A. ocean ridges

The downward part of a convection current causes a sinking force that _____. A. pulls tectonic plates toward one another B. moves plates apart from one another C. lifts and splits the lithosphere D. creates a divergent boundary

A. pulls tectonic plates toward one another

Compared to ocean crust near deep-sea trenches, crust near ocean ridges is _____. A. younger B. older C. the same age D. magnetically reversed

A. younger

Why do you think earthquakes are common along plate boundaries?

Because along plate boundaries the stress involved in plate motions cause rocks to move and break. These motions produce earthquakes.

The magma hardens, to form a small amount of ocean floor.

C.

Convection currents transfer thermal energy _____. A. between continents B. from cooler regions to warmer regions C. from warmer regions to cooler regions D. as a result of buoyancy

C. from warmer regions to cooler regions

The youngest part of the ocean floor is found _____. A. along deep-sea trenches B. where ocean sediments are thickest C. near ocean ridges D. where Earth's magnetic field changes polarity.

C. near ocean ridges

A vast, underwater mountain chain is called a(n) ____. A. deep-sea trench B. oceanic crust C. ocean ridge D. ocean floor sediment

C. ocean ridge

_____ is defined as the study of the history of Earth's magnetic field. A. paleogeography B. ocean topography C. paleomagnetism D. magnetic symmetry

C. paleomagnetism

Crust is neither destroyed nor formed along which of the following boundaries. A. convergent B. divergent C. transform D. magnetic

C. transform

Wegener's hypothesis of what stated that Earth's continents had once been joined as a single landmass.

Continental drift.

_____ is a fossil fern that helped support Wegener's hypothesis of continental drift. A. Gondwanaland B. Kannemeyerid C. Mesosaurus D. Glossopteris

D. Glossopteris

Continental-continental plate collisions produce ____. A. island arcs B. rift valleys C. deep-sea trenches D. very tall mountain ranges

D. very tall mountain ranges

A narrow, elongated depression in the seafloor.

Deep-sea trench

True or false. If two continental plates converge, a subduction zone forms.

False. An oceanic zone forms.

True or false. As new seafloor moves away from an ocean ridge, the seafloor cools and becomes less dense than the material beneath it.

False. It becomes more dense.

True or false. Some early mapmakers thought that the coastline of South America matched the coastline of Asia.

False. They thought it matched Africa.

How did Alfred Wegener use rock and fossil evident to support his hypothesis?

He showed rocks with similar features were on continents now separated by oceans. Fossils of land animals that could not fly or swim were found on different continents. Plant fossils were found in areas of climates not suitable for growth today.

Differentiate among the following terms: magnetic reversal, reversed field, and normal field.

Magnetic reversal is a changes in the orientation of the Earth's magnetic field. Reversed field is the opposite of today's field. Normal field is the same orientation (or close to it) as today's field.

Theory that states that Earth's crust and upper mantle are broken into enormous slabs.

Plate tectonics

What is the process occurring in the area of a divergent boundary.

Ridge Push. Letter R on the diagram.

What is the process that helps to move an oceanic plate toward a subduction zone?

Ridge push

A narrow, long depression in continental crust.

Rift valley

What occurs when once tectonic plates descends beneath another?

Subduction

Name each type of plate boundary and give a region where each major type of plate boundary can be found.

The three types are Divergent, Convergent, and Transform. Convergent: Himalayas Divergent: mid-ocean ridges Transform: San Andreas

Name and explain what happens at the three types of plate boundaries.

The three types are Divergent, Convergent, and Transform. Divergent: plates move apart Convergent: plates come together Transform: plates slide horizontally past each other

Type of boundary characterized by long faults and shallow earthquakes.

Transform boundary

What feature occurs where two continental crusts are moving away from each other?

A divergent boundary. Letter X on the diagram.

Explain what causes the paleomagnetic patterns on the seafloor.

As new ocean crust forms at ridges, it records the Earth's magnetic field at that time. When the magnetic field reverses, this information is also recorded.

The driving forces of tectonic plates are related to convection currents in Earth's ______. A. crust B. mantle C. inner core D. outer core

B. mantle

Each cycle of spreading and intrusion of magma during seafloor spreading results in _____. A. magnetic reversals B. new ocean crust C. subduction D. plates colliding

B. new ocean crust

A device that measures changes in Earth's magnetic field.

Magnetometer

A(n) _____ detects small changes in Earth's magnetic field.

Magnetometer.

What is a process that occurs at convergent boundaries?

Slab Pull

Explain the theory of plate tectonics.

The idea that the Earth's crust is broken into many plates that move on the Earth's mantle. They are moved by convection currents and form most of the Earth's surface features.

What early evidence suggested that Earth's continents might be moving?

The matching coastlines of the continents on either side of the Atlantic Ocean suggested that the Earth's landmasses might have once joined and moved to their present location.

Compare and contrast the three types of convergent plate boundaries.

They are Oceanic/Oceanic, Oceanic/Continental, and Continental/Continental. Oceanic/Oceanic produce island arches and subduction zones Oceanic/Continental result in subduction zones and mountain ranges. Continental/Continental form high mountain ranges

What are places where plates slide horizontally past each other?

Transform boundary.

True or false. Scientists at the time rejected Wegener's hypothesis of continental drift because he could not explain how or why Earth's continents move.

True.

True or false. The transfer of thermal energy by the movement of warmed matter is called convection.

True.