Plate Tectonics and Earth's Interior

Question 1

Outer to inner layers of Earth:

Answer 1

crust (solid), mantle (solid), outer core (liquid), inner core (solid)

Question 2

What are earthquakes caused by?

Answer 2

A sudden release of energy from rocks breaking

Question 3

How is the energy of earthquakes dispersed?

Answer 3

through seismic waves, which are recorded by seismographs

Question 4

Different types of seismic waves travel through the Earth at:

Answer 4

different velocities and move in different ways

Question 5

P-wave

Answer 5

• compression-extension (side-to-side movement) like pushing water
• travels through fluids

Question 6

S-wave

Answer 6

• shear

- does not travel through fluids

Question 7

Seismic wave velocities are changed by:

Answer 7

changes in density, which deflect the waves, causes paths to change direction at layer boundaries

Question 8

No S-waves are recorded on the other side of the planet after an Earthquake, therefore:

Answer 8

there must be a liquid layer in the Earth

Question 9

Scientists have modelled the layered internal structure of the earth by:

Answer 9

Assessing the changes in speed and amount of deflection of different seismic waves

Question 10

Composition of the crust

Answer 10

• 46% O, 28% Si, Al 8%, Fe 6%, Mg 4%, etc.

- is stiff and solid

Question 11

Composition of the whole Earth

Answer 11

• Fe 35%, O 30%, Si 15%, Mg 13%, Ni 2.4%, etc.

Question 12

How do we know the composition of the whole Earth?

Answer 12

• Seismic data, tells us about density
• Samples of volcanic rock that contain pieces of the mantle
• Samples of meteorites that likely reflect the internal composition of Earth

Question 13

Earth differentiated itself based on:

Answer 13

density, less dense = float (like O), and more dense sink

Question 14

How did the layers of the Earth form?

Answer 14

1. Heating from bombardment
2. Gravitational compression (increases with mass)
3. Radioactive decay produced melt

Question 15

Two types of crust are:

Answer 15

1. Continental crust (10-70km thicc), thick and rich in Si and Al, low density
2. Oceanic crust (5-7km thicc), thin, rich in Fe and Mg, higher density

Question 16

As we go further down in the Earth:

Answer 16

Pressure, temp, and density increase leading to differences in phase and mechanical behaviour

Question 17

Compositional layers:

Answer 17

Continental crust, oceanic crust, mantle, core

Question 18

Mechanical layers:

Answer 18

From top to centre of the earth: 
lithosphere (10-200km) 
aesthenosphere (200-660km) 
mesosphere (660-2900km) 
outer core (2900-5150km)
inner core (5150-6396km)

Question 19

Mantle characteristics:

Answer 19

• Solid
• Uppermost mantle: stiff
• Aesthenosphere: soft, can flow (like plastic)
• Mesosphere: stiffer than the asthenosphere, but can still flow

Question 20

Lithosphere characteristics:

Answer 20

• Solid and stiff
• Composed of uppermost mantle and crust
• Uppermost mantle is stuck to the base of the crust
• Earth’s outer shell is broken into lithospheric plates
• Plates move and interact in response to forces within the earth
• Plates move 0-10cm/year

Question 21

What are plate boundaries?

Answer 21

The place where two plates meet

Question 22

Plate boundaries are named based on:

Answer 22

The relative motion of the plates on either side of the boundary

Question 23

Transform boundary:

Answer 23

• The plates grind past each other laterally
• Commonly associated with spreading centres (divergent boundaries), they connect spreading ridges
• No crust created or destroyed

Question 24

Divergent boundary:

Answer 24

The plates move away from each other

Question 25

Convergent boundary:

Answer 25

The plates move towards each other

Question 26

Position of volcanoes and earthquakes are strongly linked to:

Answer 26

Plate boundaries

Question 27

Volcanoes typically occur at what type of boundaries?

Answer 27

Divergent and convergent boundaries

Question 28

Earthquakes appear at what type of boundaries?

Answer 28

All 3 types

Question 29

Divergent boundary characteristics:

Answer 29

• Can exist on land, but mostly exist on the seafloor
• Seafloor spreading produces a continuous row of volcanoes called a mid-ocean ridge that wraps around the world
• Rocks get older (and COLDER/denser) as you move perpendicular away from the ridge (new rocks forming at ridge b/c lava is cooling, HIGH topography)

Question 30

Land-ocean convergent boundary

Answer 30

• Subducting plates go under continental plate b/c continental crust is less dense
• Accretionary prism: loose materials gathering from being scraped off top of subducting plate
• Partial melting (from water lowering melting point) creates less dense liquid rock = TURNS INTO MAGMA POCKETS
• As the plate is subducting, LOTS of earthquakes = easy to map

Question 31

Ocean-ocean convergent boundary

Answer 31

• More dense oceanic plate will subduct under less dense oceanic plate

Question 32

Continent-continent convergent boundary

Answer 32

• No plate is subducted = “car crash” = MOUNTAINS

Question 33

Convection

Answer 33

• Hot water rises, cool sinks = loop
• Heat is transferred through the mantle via convection
• Heat is one of the sources of plate movement

Question 34

Plates are likely to move because:

Answer 34

1. Asthenosphere is weak so lithosphere can slip over it

2. Oceanic plates are dense so they dive under continental plates

Question 35

Dominant forces causing plate movement seem to be:

Answer 35

A) Plates pull down into trenches (slab pull)
B) Plates driven down the slope from ridge to trench by gravity (ridge push)
- Rising magma pushes the plate apart, the weight of the falling lithosphere pulls the plate along, gravity causes the plate to slide down the gentle slope

Question 36

Opening an ocean

Answer 36

• Plates are pulled apart
• Rift valley form
• Magma erupts from the mantle, adding new oceanic crust to the plate margin
• Lows fill with water
• Continued spreading creates new ocean

Question 37

Closing an ocean

Answer 37

• Plates recycled into the mantle via subduction
• Plates brought gradually closer together
• Continents collide, the ocean is closed