2Nd Semester Ch 17 Science Tectonic Plates

Front 1

The ______ and _______ of the continents suggests that they were once joined together

Back 1

the geology and the shape of the continents suggests that they were once connected

Front 2

What is continental drift?

Back 2

Continental drift is the idea that Wegener developed which proposed that Earth's continents had once been joined as a single landmass that broke apart and sent the continents adrift.

Front 3

What is Pangaea?

Back 3

Pangaea is the supercontinent that began to break apart about 200 mya. The continents have slowly begun to move to their present positions.

Front 4

What was some evidence that Wegener used to support his hypothesis about continental drift and Pangaea?

Back 4

Evidence included evidence from rock formations: (where Pangaea began to break apart, large geologic structures, such as mountain ranges, fractured as the continents separated. There were different rock types on opposing sides of the Atlantic Ocean.)
Evidence From Fossils: Similar fossils of several different animals and plants that once lived on or near land had been found on widely separated continents. Animals that dwelled there could not have swum the distance to the other continents.
Climatic Evidence: Fossils were found on different sides of Earth. The area separating these fossils was too large to have had a single climate.
Coal Deposits: The existence of coal beds in Antarctica indicated that this frozen land had once had a tropical climate. Wegener used this to conclude that Antarctica must have been closer to the equator in geologic past.
Glacial Deposits: In places such as Australia, S America, Africa, and India, the presence of glacial deposits suggest that these areas were once covered by a think ice cap similar to that in Antarctica today. They had to have once been located near the south pole because those areas are too warm to have had glaciers at their current positions.

Front 5

What were two major flaws that prevented continental drift from being widely accepted by the scientific community back in the time of Wegener?

Back 5

What forces could cause the movement and how continents could move through solids were the main questions.

Front 6

Where does oceanic crust form?

Back 6

Oceanic crust forms at ocean ridges.

Front 7

What is a magnetometer?

Back 7

A magnetometer is a device that can detect the magnetic field generated by ocean floor rocks.

Front 8

What natural happenings are common among ocean ridges?

Back 8

volcanism and earthquakes

Front 9

What is a deep-sea trench?

Back 9

A deep-sea trench is a narrow, elongated depression in the seafloor

Front 10

What is the deepest trench?

Back 10

The deepest trench is the Marianas Trench

Front 11

Compare the rock samples that are taken from near the deep-sea trenches to the rock samples that are taken from near the ocean ridges.

Back 11

The rocks that are near the ridges are younger, and as they go toward the trenches, the rock is older. Age increases with distance from the ridge

Front 12

Observations of ocean-floor sediments revealed that the thickness of the sediments ________ with distance away from an ocean ridge

Back 12

the thickness increases with distance away from a ridge

Front 13

What is a magnetic reversal?

Back 13

A magnetic reversal is when the flow in the outer core changes, and Earth's magnetic field changes direction. This would cause compasses to point to the south. These have occurred many times in Earth's history.

Front 14

What is normal polarity as opposed to reversed polarity.

Back 14

Normal polarity occurs when the magnetic field is the same as it is at present. Reversed polarity is when the magnetic field is the opposite of the present field.

Front 15

What is paleomagnetism?

Back 15

Paleomagnetism is the study of the history of Earth's magnetic field.

Front 16

Oceanic crust is mostly what kind of rock?

Back 16

basaltic, which contains large amounts of iron-bearing minerals of volcanic origin.

Front 17

What is an isochron?

Back 17

An isochron is an imaginary line on a map that shows points that have the same age, meaning they formed at the same time.

Front 18

What is seafloor spreading?

Back 18

Seafloor spreading is the process by which new oceanic crust forms at ocean ridges and slowly moves away from the spreading center until it is subducted and recycled at deep-sea trenches.

Front 19

What happens during seafloor spreading?

Back 19

During seafloor spreading, magma, which is hotter and less dense than surrounding mantle material, is forced toward the surface of the crust along an ocean ridge. As the two sides of the ridge spread apart, the rising magma fills the gap that is created. When the magma solidifies, a small amount of new ocean floor is added to Earth's surface. As spreading along a ridge continues, more magma is forced upward and solidifies. This cycle of spreading and the intrusion of magma continues the formation of ocean floor, which slowly moves away from the ridge.
seafloor spreading was the evidence that Wegener needed to complete his model of continental drift. Continents are like passengers that ride along while ocean crust slowly moves away from ocean ridges.

Front 20

Volcanoes, mountains, and deep-sea trenches form where?

Back 20

at the boundaries between tectonic plates.

Front 21

What are tectonic plates?

Back 21

Tectonic plates are huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth's surface.

Front 22

How many major plates are there on earth?

Back 22

there are twelve major plates

Front 23

What is a divergent boundary?

Back 23

Divergent boundaries occur where tectonic plates move away from each other.

Front 24

Where do divergent boundaries occur?

Back 24

Divergent boundaries commonly are seen along the ocean floor where in rift valleys

Front 25

What does a mid-ocean ridge appear to be?

Back 25

A mid ocean ridge appears to be a continuous mountain chain on the ocean floor

Front 26

What is a rift valley?

Back 26

A rift valley is when continental crust begins to separate, the stretched crust forms a long, narrow depression, which is a rift valley.

Front 27

What are convergent boundaries?

Back 27

Convergent boundaries are when two tectonic plates are moving toward one another.

Front 28

What is subduction?

Back 28

When two plates collide, the denser plate eventually descends below the less dense plate

Front 29

What are the three types of convergent boundaries?

Back 29

Oceanic-oceanic
Continental-continental
and
Oceanic-continental

Front 30

What is an Oceanic Oceanic Convergent boundary?

Back 30

An oceanic oceanic convergent boundary is when a subduction zone is formed when one oceanic plate which is denser as a result of cooling, descends below the other oceanic plate. The process of subduction creates an ocean trench

Front 31

What is an oceanic-continental convergent boundary?

Back 31

An oceanic-continental boundary is when subduction zones are also found where an oceanic plate converges with a continental plate. The denser oceanic plate is subducted. This also produces a trench and volcanic arc. However, instead of forming an arc of volcanic islands, oceanic-continental convergence results in a chain of volcanoes along the edge of the continental plate. The result of thes type of subduction is a mountain range with many volcanoes.

Front 32

What is a continental continental convergent boundary?

Back 32

A continental continental convergent boundary forms when two continental plates collide. These form long after an oceanic plate has converged with a continental plate. Continents are often carried along attached to oceanic crust. Over time, and oceanic plate can be completely subducted, dragging an attached continent behind it toward the subduction zone.

Front 33

What is a transform boundary?

Back 33

A transform boundary is a region where two plates slide horizontally past each other. They are characterized by long faults, sometimes hundreds of kilometers in length and by shallow earthquakes. Transform boundaries were named for the way Earth's crust changes, or transforms, its relative direction and velocity from one side of the boundary to the other. New crust is formed at divergent boundaries and destroyed at convergent boundaries. Crust is only deformed or fractured somewhat along transform boundaries

Front 34

What is probably the best known example of a transform boundary?

Back 34

The San Andreas Fault.

Front 35

What causes plate motions?

Back 35

Convection Currents in the mantle.

Front 36

What is Earth's mantle?

Back 36

Earth's mantle is earth's interior between its core and crust

Front 37

What is convection?

Back 37

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

Front 38

What is ridge push?

Back 38

Ridge push happens 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 the process of ridge push.

Front 39

What is slab pull?

Back 39

Slab pull is when the weight of a subducting plate pulls the trailing slab into the subduction zone much like a tablecloth slipping off of a table can pull articles off with it. It is likely that combination of mechanisms such as these are involved in plate motions at subduction zones.