Plate Tectonics

Question 1

What is the inner core of Earth?

Answer 1

A solid mass of iron and nickel

Question 2

How does the inner core provide Earth’s internal energy?

Answer 2

• High pressure
• Radioactive decay of elements such as uranium

Question 3

What is the outer core of Earth?

Answer 3

A semi-molten mass of iron and nickel

Question 4

What is the mantle?

Answer 4

The thickest layer of Earth composed mainly of solid rock

Question 5

What is the asthenosphere?

Answer 5

The semi-molten upper layer of the mantle which moves through convection currents generated by heat from Earth’s core

Question 6

What is the lithosphere?

Answer 6

The uppermost part of the mantle and the crust

Question 7

What is the crust?

Answer 7

The outermost layer of Earth’s core which is divided into tectonic plates

Question 8

What are the two types of tectonic plates?

Answer 8

• Continental
• Oceanic

Question 9

What are the characteristics of continental plates?

Answer 9

• Granitic rock
• 25-75km thick
• Less dense
• Lighter

Question 10

What are the characteristics of oceanic plates?

Answer 10

• Basaltic rock
• 7-10km thick
• Denser
• Heavier

Question 11

What is the theory of continental drift?

Answer 11

Alfreg Wegner suggested that continents move over Earth’s surface and were once connected as a super-continent (Pangea)

Question 12

What is the geological evidence for continental drift?

Answer 12

• Identical geology in Scotland and Eastern Canada
• Tropical coal deposits found in the UK and North America

Question 13

What are convection currents?

Answer 13

• Hot magma rises and spreads out under plates
• As magma cools, it becomes denser and sinks

Question 14

What is ridge push and slab pull?

Answer 14

A gravity-driven system of plate movement

Question 15

What is the process of ridge push?

Answer 15

Magma rises at constructive plate boundaries and solidifies to create new crust material, before sliding away from the ridge

Question 16

What is the process of slab pull?

Answer 16

Dense, oceanic plates are subducted at destructive plate boundaries, pulling the rest of the plate along with it

Question 17

What is another name for ridge push?

Answer 17

Gravitational sliding

Question 18

What is sea floor spreading?

Answer 18

The theory that as plates move away from each other at constructive margins, the crust must be destroyed elsewhere

Question 19

How is the lithosphere divided?

Answer 19

• 7 large plates
• 3 smaller plates

Question 20

What is paleomagnetism?

Answer 20

A supporting theory to sea floor spreading at mid-ocean ridges due to signals of past reversals in Earth’s magnetic field within the crust

Question 21

What are the four types of plate boundary?

Answer 21

• Destructive subduction
• Destructive collision
• Constructive
• Conservative

Question 22

What happens at a destructive subduction boundary?

Answer 22

A denser oceanic plate subducts beneath a continental or less dense oceanic plate (e.g. South American and Nazca plates)

Question 23

What happens at a destructive collision boundary?

Answer 23

Two continental plates meet and no subduction occurs. Instead, the sediment crumples and forms fold mountains (e.g. Eurasian and Indian plates)

Question 24

What happens at a constructive boundary?

Answer 24

Two plates diverge and new crust is created as magma rises and solidifies through the gap

Question 25

What happens at a conservative boundary?

Answer 25

Two plates slide past each other at different speeds without creating or destroying crust

Question 26

What is the link between convection currents and gravitational sliding?

Answer 26

It is believed that convection currents only play a small role in plate movement, as it is mostly driven by gravity

Question 27

What landforms occur at destructive subduction boundaries?

Answer 27

• Island arcs
• Ocean trenches

Question 28

How do island arcs form?

Answer 28

• Plate melts as it is subducted
• Melted material is less dense and rises to the surface as plutons of magma
• This forms explosive volcanoes at the surface
• Eruptions form volcanic islands (e.g. Mariana islands)

Question 29

How do ocean trenches form?

Answer 29

Subduction between either two O plates or an O and a C plate (e.g. Mariana Trench)

Question 29

What landform occurs at a destructive collision boundary?

Answer 29

Fold mountains

Question 30

How do fold mountains form?

Answer 30

• Two C plates converge
• Neither is subducted as they are of similar density
• Sediment crumples upwards to form mountains (e.g. the Himalayas)

Question 31

What landforms occur at constructive boundaries?

Answer 31

• Ocean ridges
• Rift valleys

Question 32

How do ocean ridges form?

Answer 32

• Two O plates move away from each other
• Basaltic magma rises and solidifies to form a ridge
• Surtsey Island, Iceland

Question 33

How do rift valleys form?

Answer 33

• Two C plates move away from each other
• New crust is created as andesitic magma rises
• Brittle crust can fracture and create parallel faults (e.g. East African Rift Valley)

Question 34

What is an example of a conservative plate boundary?

Answer 34

San Andreas Fault, USA

Question 35

What is a hotspot?

Answer 35

Areas where magma plumes rise and weaken the crust, both feeding volcanoes as well as forming volcanic island chains (e.g. Hawaii)

Question 36

What is the difference between island arcs and volcanic island chains?

Answer 36

Island arcs occur at subduction zones whereas volcanic island chains occur at hotspots

Question 37

How are volcanic island chains formed?

Answer 37

• Magma plume creates a hotspot
• Volcanoes can form as the crust is burnt
• Plate movement drags the head of the hotspot
• Volcanoes in the chain increase in age