8Th Grade Earth Science: Chapter 3 And 4 Plate Tectonics And Earthquakes

Front 1

What was Alfred Wegner's hypothesis about the continents?

Back 1

Wegner's hypothesis was that all the continents were once joined together in a single landmass and have since drifted apart.

Front 2

What are mid-ocean ridges?

Back 2

Mid-ocean ridges form when long-chains of mountains that rise up from the ocean floor.

Front 3

What is sea-floor spreading?

Back 3

Sea-floor spreading adds more crust to the ocean floor. At the same time, older strips of rock move outward from either side of the ridge

Front 4

What happens at deep-ocean trenches?

Back 4

In a process of tens of millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.

Front 5

What is the theory of plate tectonics?

Back 5

The theory of plate tectonics states that Earth's plates are in slow, constant motion driven by convection currents in the mantle.

Front 6

How does stress change earth's crust?

Back 6

Tension, compression, and shearing work over millions of years to change the shape and volume of rock.

Front 7

How do faults form?

Back 7

When enough stress builds up in rock, the rock breaks creating a fault.

Front 8

How does plate movements create new landforms?

Back 8

Over millions of years, the forces of plate movement can change a flat plain into features such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

Front 9

What are seismic waves?

Back 9

Seismic waves are vibrations similar to sound waves. They travel through Earth carrying energy released by an earthquake?

Front 10

How are earthquakes measured?

Back 10

The amount of an earthquake's damages or shaking that is felt is rated using the Modified Mercalli scale. The magnitude or scale of an earthquake is measured on a seismograph using the Ricter scale or moment magnitude scale.

Front 11

How is an epicenter located?

Back 11

Geologists use seismic wave to locate an earthquake's epicenter.

Front 12

How did Wegner's hypothesis turn into the theory of plate tectonics?

Back 12

Scientists looked at his hypothesis and given time and new understandings(fossils and plants of plate movement. It turned into the theory of plate tectonics.

Front 13

What is the relationship between mid-ocean ridges, sea-floor spreading, and deep ocean trenches?

Back 13

New crust forms at mid-ocean ridges during the process of sea-floor spreading. During sea-floor spreading, the crusts spreads down and through the deep ocean trenches, the crust is subducted.

Front 14

What is the relationship between the stresses in Earth's crust and the formation of faults?

Back 14

The three stresses(tension, compression, and shearing) are stresses that break rocks which are known as faults.

Front 15

How does stress and movement along faults create new landforms?

Back 15

Tension pulls the rock apart. Compression smashes rock together. Shearing grinds rock between plates.

Front 16

What causes the movement and destruction we see and feel in an earthquake?

Back 16

The release of energy through the movement of tectonic plates.

Front 17

What is subduction, how does it work, why does it happen?

Back 17

Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle again. As subduction occurs, crust closer to a mid-ocean ridge moves away from the ridge and toward a deep-ocean trench. Subduction occurs because the oceanic crust is cooler and denser than the continental crust which is hotter and less dense.

Front 18

Why is the continental crust less dense than the oceanic crust?

Back 18

The continental crust contains granite which is less dense than the oceanic crust which contains basalt.

Front 19

Why does the old crust subduct?

Back 19

It cools and becomes more dense as it cools.

Front 20

What is the relationship between subduction and earth's oceans?

Back 20

Sea-floor spreading can change the size and shape of oceans.The size of the oceans are determined by how fast new crust is being created at mid-ocean ridges and how fast old crust is being swallowed up at deep-ocean trenches.Oceans surrounded by trenches may shrink. Oceans with few trenches will probably grow larger.

Front 21

What are the three types of stress?

Back 21

Tension Stress, Compression Stress and Shearing Stress

Front 22

What are the three types of fault lines?

Back 22

Strike/slip Fault, Normal Fault, and Reverse Fault

Front 23

What are the three types of fault boundaries?

Back 23

Divergent Boundary, Transform Boundary, Convergent Boundary

Front 24

What type of stress creates each fault?

Back 24

Tension creates a normal fault. Compression creates a reverse fault. Shearing creates an strike/slip fault.

Front 25

What happens in a each type of fault?

Back 25

In a normal fault,the hanging wall moves down and the foot wall moves up. In a reverse fault, the hanging wall moves up and the foot wall moves down. In a strike/slip fault, the tectonic plates strike and slip past each other.