Chapter 17- Science
The Mid-Atlantic Ridge is an example of a
divergent boundary
True or False: The oldest ocean floor rocks are about *3.8 billion* years old.
180 million
A field with the same orientation as today's field is said to have ____.
Normal polarity
True or False: *Deep-sea trenches* are vast, underwater mountain chains.
Ocean ridges
Number these steps in the order they occur- seafloor spreading: ____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
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 forces pulls plates downward at convergent boundaries.
Where are most divergent boundaries formed?
on the seafloor
Coal beds in Antarctica indicated to Wegener that this continent was
once located closer to the equator
To support his hypothesis of continental drift, 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
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 whereby the weight of a subducting plate helps to pull the trailing lithosphere into the subduction zone.
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.
What is one hypothesis regarding the formation of a divergent boundary on a continent?
Large continental masses may act as insulating blankets. The underlying mantle becomes warmer and causes the upward leg of a convection current to develop. Over time, the continent splits.
A field that is opposite the present field has ____.
Reversed polarity
True or False: Earthquake activity and volcanism are common along *ocean ridges.*
True
When the ocean floor's magnetic readings match the present field, the 2 fields _____. This produces a _______ than normal reading.
combine, stronger
Based on observations of fossils of Glossopteris, Wegener concluded that
continental rocks containing these fossils had once been joined
Places where tectonic plates move apart are called
divergent boundaries
Was constructed from data gathered from continental basalt flows
geomagnetic time scale
Fossil evidence that supported Wegener's idea of continental drift included
land-dwelling animals
Based on the glacial deposits he observed, Wegener argued that
landmasses drifted away from the south pole
Each cycle of spreading and magma intrusion along an ocean ridge results in the formation of this
new ocean crust
Convergent boundaries are classified according to the
type of crust involved
Which of the following best describes what happens when an oceanic plate converges with a continental plate?
A trench and a mountain range with many volcanoes form
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 matter is pulled downward as a result of gravity. This up and down flow creates a convection current.
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
Earth's ____ has changed over time.
Magnetic field
True or False: An *isocron* is a change in Earth's magnetic field.
Magnetic reversal
True or False: *Sonar* uses sound waves to measure water depth
True
True or False: The magnetic patterns on either side of a *deep-sea trench* are mirror images of each other.
True
What feature is associated with a continental-continental plate boundary?
a mountain range
What landform result from divergence of continental crust?
a rift valley
Pangaea was an ancient supercontinent made up of
all of Earth's continents
Oceanic crust is made mostly of
basalt
When the magnetic readings of the ocean floor are reversed compared to today's field, the 2 fields partially _____ to produce a ____ than normal reading.
cancel, lower
True or False: The thickness of ocean floor sediments *decreases* with distance from an ocean ridge.
increases
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
Magnetic data of the ocean floor has been used to generate _____ maps, which have shown the ocean floor is ______ near ocean ridges and _____ near deep-sea trenches.
isochron, younger, older
Device that can detect small changes in magnetic fields
magnetometer
Early mapmakers thought continents might have moved based on their observations of
matching coastlines
What can happen when 2 oceanic plates converge and one is subducted into the mantle?
melted magma erupts and forms an arc of islands
Which theory states that Earth's crust and rigid upper mantle move in different directions and at different rates over Earth's surface?
plate tectonics
Fossils of aquatic reptiles found in freshwater rocks suggested to Wegener that these reptiles
probably did not cross the ocean
True or False: The theory of *continental drift* states that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches.
seafloor spreading
Which of the following features forms when oceanic plates converge?
subduction zones
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 ocena crust as it moves away from ocean ridges.*
True
Tectonic plates interact at places called plate
boundaries
Places where tectonic plates come together are called
convergent boundaries
True or False: As new seafloor is carried away from an ocean ridge, it *heats up, expands, and becomes less dense* than the material beneath it.
cools, contracts, and becomes more dense
Most scientists at the time rejected Wegener's hypothesis of continental drift because he
couldn't explain how or why the continents moved
At which tectonic plate boundary do plates slide horizontally past each other?
transform boundary
True or False: Rock samples taken near ocean ridges are *older* than rock samples taken near deep-sea trenches.
younger