Chapter 9 Earth Science
Paleomagnetism
A record of ______ is preserved in the sequence of rock strips at ocean ridges.
Youngest, older
According to the deep ocean drilling project findings the ____ crust was near the oceanic ridges while the ____ was further away.
Trench
An ocean ____ is a surface feature produced by a descending plate.
Paleomagnetism
Ancient magnetism
Younger
Are the rocks closer to the Mid-Atlantic Ridge younger or older?
Ocean floor, valleys, deep ocean trenches
As scientists mapped the _____ using sonar, they found long, curved ____ along the edges of some ocean basins called _______
Transform fault boundary
At a ______, plates grind past each other without destroying the lithosphere.
Grind, lithosphere
At a transform fault boundary, plates grind past each other without destroying the ____.
Collide
At convergent boundaries plates ____.
Collide and interact
At convergent boundaries, plates ______, producing features including trenches, volcanos, and mountain regions.
Mid-ocean ridges, land
Most transform fault boundaries occur at _____, however some occur on ____ like the San Andreas Fault.
Sea floor spreading
New material is added to edges of diverging boundaries as the plates separate in a process called ____.
180 million years old, subductes
No ocean crust is found to be older than _____ because it eventually _____ into the mantle.
Mesosaurus
Scientists think that the _____ lived in fresh water lakes and shallow bays.
Rift Valley
The low point in the middle of a diverging boundary is known as a ____.
Sea floor spreading
The magnetic reversals "frozen" into the ocean floor are evidence for _____.
Earthquakes
The pattern of _____ at plate boundaries suggests the movement of the lithosphere.
Rock types and mountain belts
The picture in the continental drift puzzle is one of matching ______.
Slab pull, ridge push, mantle plumes
The sinking of cold ocean lithosphere directly drives the motions of mantle convection through _____ and _____. Some scientists think _____ are involved in the upward flow of rock in the mantle.
Magnetic banding on the sea floor, earthquake patterns, and age of ocean floor rock
The three evidences for plate tectonics are ____, ____, and ____.
Ocean-ocean, ocean-continent, continent-continent
The three types of converging plate boundaries are ____,____, and ____.
Divergent, convergent, transform
The three types of plate boundaries are ____,____, and ____.
Combination, three
There are three types of plate boundaries. Each plate contains a ____ of the ____ types.
Oceanic-continental, denser, less dense
What two types of plates interact when the ____ oceanic plate subducts below ____ continental slab.
Convergent plate boundaries
What type of plate boundaries produce trenches, volcanos, and mountain regions?
Oceanic, subducting
When two ____ slabs converge, the ____ plate causes volcanic activity which can build a chain of islands called a volcanic island arc.
Continental, continents
When two pieces of ____ lithosphere collide, the two ____ eventually merge, creating complex mountains.
Diverging
Where heat is rising in the mantle a ____ boundary is created at the surface.
Right in the center
Where is the Rift Valley located in the diverging boundary?
Converging
Where material in the mantle is cooling and sinking, _____ boundaries are created at the surface.
Because basalt is denser than granit
Why is oceanic crust denser than continental?
Transform fault boundaries
____ occur where two plates grind past each other.
Divergent boundaries
____ occur where two tectonic plates move away from each other.
Fossil evidence, fossils
_____ for continental drift includes several ____ organisms found on different landmasses.
Mid-ocean ridge
_____ is a long chain of mountains extending the length of the ocean.
Alfred Wegener
_____ produced a hypothesis in 1916 about a supercontinent breaking apart 200 mya.
Convection currents
______ in the mantle provide the basic driving forces for plate motions.
Plate Tectonics
What theory eventually proved that Wegener was correct?
Continental volcanic arc, eruption
A ____ is a range of volcanic mountains produced in part by the subduction of oceanic lithosphere which melts, rises, and may reach the surface causing ____.
Mantle plume
A ____ is a rising column of hot, solid mantle rock at a hot spot.
Subducted
Before continents collide ocean basin between them is ____.
Asthenosphere
Below the lithosphere is the _____ which allows for motion of the plates.
Younger
Compared to the continents the ocean crust is geologically ____.
Destructive
Convergent plate boundaries are known as ____ margins.
Continental drift
Matching types of rock in several mountain belts that today are separated by oceans provide evidence for ____.
Land bridges
In Wegener's time, the idea of ____ was the accepted explanation for similar fossils being found on different land masses.
Sonar
What stands for sound navigation and ranging?
Magnetometers, parallel, basalt, slowly
Ships tow ____ across the ocean floor. Data shows alternating bands of magnetized strips ____ to the diverging center. Proves that new ____ forms at the center, solidifies with polarity at the time and then ____ moves aside as new magma reaches the surface to take its place.
Continents
Some spreading centers, however, occur on the ____ (Great Rift Valley in East Africa).
False
T/F Transform boundaries are known as constructive margins.
False
T/F. Diverging boundaries only exist on ocean plates.
South America and Africa
Wegener agreed that _____ must have been joined.
5 cm/year
What are the rates of sea- floor spreading?
Acquire, time, paleomagnetism
(Earth's Magnetic field) As certain rocks form, they ___ the polarity that earth's magnetic field has at the ___. They posses ____ (ancient magnetism).
Constructive, created
Divergent plate boundaries are also known as _____ margins because crust is _____.
Mid-ocean ridge system, 7,000
Earth's ____ forms the longest features on Earth's surface. The system winds more than ____ kilometers through all the major ocean basins like the seam on a baseball.
Plates
Earth's lithosphere is divided into ____ that move and change shape.
Polarity
Earth's magnetic field occasionally reverses ____.
Ocean ridges
Elevated areas of the seafloor called ____ occur along well-developed divergent plate boundaries.
200 million years ago
Wegener also hypothesized that about _____ Pangaea began breaking into smaller continents.
220, 300, southern, glacial
Wegener found glacial deposits showing that between ____ million and ____ million years ago, ice sheets covered large areas of the _____ hemisphere. Deposits of ____ till occurred at latitudes that today have temperate or even tropical climates: Southern Africa, South America, India, and Australia.
Pangea
Wegener proposed that in the past, the continents were joined to form a supercontinent he named ______
Crossed the vast ocean
Wegener reasoned that these organisms could not have _____ presently separating the continents.
Continental drift
Wegener's _____ hypothesis proposed that the continents changed position on Earth's surface.
Mechanism
Wegener's hypothesis was rejected because he could not describe a _____ for continental drift.
Energy released by radioactive isotopes in the mantle and heat from the core itself
What are the heat sources for mantle convection?
Divergent boundaries
What boundaries are also known as constructive boundaries and spreading centers?
All land
What does Pangaea mean?
The crust and upper most mantle
What is the lithosphere?
The older rocks are more distant from the ridge
What is the relationship between the age of rocks on the ocean floor and their distance from the Mid-Atlantic Ridge?
Paleomagnetism
What means ancient or old magnetism?
Convergent
What plate boundaries are considers destructive?
Continental drift
What was Wegener's radical hypothesis that he proposed?
Puzzle fit of continents, matching fossils and matching rock types, ancient glacial evidence/climate
What were Wegeners three evidences that he used to support his "Pangea" hypothesis?
Trench
When an oceanic plate collides with another plate a ____ forms where the plates meet.
Subducted, mantle(asthenosphere)
When oceanic plates converge with another plate the lithosphere is ____ below in the _____.
Mesosaurus
The distribution of ____ fossils supported the argument hat South America and Africa had once been joined.
Convection currents, asthenosphere
The driving force of the plate motions is ____ in the _____.
Plastic, slowly
The hot, but solid rock of the mantle behaves in a ____ way-that is, it can flow ____ over geologic times.
Rift Valley
A _____ is a deep, central valley (long canyon) that runs down the center of a ridge.
Flow, fluid, density
A convection current is the continuous ___ that occurs in a ____ because of differences in ___.
Density
A convection current is the movement of materials because of differences in ____.
Youngest, oldest, 180 million years old
Deep sea drilling from both sides of mid-ocean ridges confirmed that ocean floor is ____ along rift valley and ___ near subduction zones and edges of continents. None of floor older than _____ because it gets subductes into the mantle.
Trench, focus
Depth -shallow focus near ___; deep ___ far from trench implies that subducting plate below the surface.
Subduction zones
Destructive plate margins called ____ are where one oceanic plate is forced down into the mantle beneth a second plate.
Different
Fossil evidence for continental drift includes several fossil organisms found on ____ land masses.
Moon, tidal/gravitational, ice-breaker
He theorized incorrectly that the ___ provided enough ___ influence to move the continents through the ocean floor much like ____ ships cut through sea ice.
Because as the ocean expands the older rock gets pushed further away from the ridge
How does seafloor spreading explain why the youngest rocks are found near the Mid-Atlantic Ridge?
Age and type
If the continents were once part of Pangaea, the rocks found in a particular region on one continent should closely match in _____ those in adjacent positions in the adjoining continent.
Ridge push, asthenosphere
In ____, the stiff ocean lithosphere slides down the _____ that is elevated near mid-ocean ridges.
Continental volcanic arc, overriding
In an ocean-continent collision, ____ form on the nonsubducting (______) plate.
Ocean plate (always)
In an ocean-continent collision, which plate will be the subducting plate?
Volcanic island arcs, nonsubducting
In an ocean-ocean convergent boundary, ____ will form on the ____ (overriding) plate.
Apart
In divergent boundaries plates move ____.
Whole mantle convection, lower mantle, mantle, millions
In the process called _____, rock rises from the ____ toward the top of the ___, then sinks back down. This process takes ____ of years
Sea-floor, outward
In the process of ____, new ocean floor forms along Earth's mid-ocean ridges, moves slowly ____ across ocean basins, and finally sinks (subducts) back into the mantle beneath deep-ocean trenches at subduction zones.
Lithospheric, slowly, convection currents
In the theory of plate tectonics, Earth's ____ plates move ____ relative to each other, driven by ____ in the mantle
Slide/glide past
In transform boundaries, plates ____ one another.
Himalayas
India-Asia=>____.
Mid-ocean ridges
Many transform fault boundaries are found at ____.
Spreading centers
Most divergent boundaries are _____ located along the crests of mid-ocean ridges.
Lithosphere
Plate tectonics involves the earth's rigid outer shell or _____.
Lithosphere
The ____ is broken into several huge pieces, called plates.
Deeper, longer
The ____ the water, the ____ it takes the sound waves to bounce off the ocean floor back to the ship.
Drifted slowly
The continents then _____ to their present positions.
Convergent boundaries
Where two plates move together, _____ occur
The ocean is crust is denser
Why is the oceanic plate the subducting one?
Marianas
____ 11km deep.
Divergent boundaries
____ are found where two of Earth's plates move apart.
Convergent boundaries
____ form where two plates move together.
Matching types of rock
____ in several mountain belts that today are separated by oceans provide evidence for ____.(Appalachians and Caledonians)
Sonar
____ is a system that made it easier to map the ocean floor by using sound waves to calculate the distance to an object.
Deep faults
____ separate the different plates.
Paleomagnetism
______ is preserved in lava flows.