Theory of Plate Tectonics

Question 1

Who came up with the theory of continental drift?

Answer 1

Alfred Wegener

Question 2

What is the lithosphere?

Answer 2

the solid rock making up the crust and upper part of the mantle

Question 3

How do fossils provide evidence of continental drift?

Answer 3

• fossils of species found on different, separate continents
• not able to travel by air/sea
• continents previously must have been closer
• e.g mesosaurus

Question 4

How does jigsaw fit provide evidence for continental drift?

Answer 4

• continents look as if they fit together
• suggests at one point they were joined

Question 5

Explain how paleo-magnetism shows sea-floor spreading

Answer 5

• iron-rich minerals in lava, rise through crust
• these align with magnetic field at the time
• lava cools and sets in this alignment
• polarity is able to be recorded, changes every 400,000 years
• symmetry in the bands of lava suggest sea floor is spreading

Question 6

What are 3 things that cause plate movement?

Answer 6

• convection currents
• ridge push
• slab pull

Question 7

Briefly outline how convection currents move plates

Answer 7

• radiogenic heat causes magma to become hot and less dense. It rises
• when near the lithosphere, it cools and becomes more dense. It sinks
• circular currents in asthenosphere drive movement in lithosphere.

Question 8

Briefly outline how ridge push causes plate movement

Answer 8

• hot magma rises and causes the asthenosphere and lithosphere expand and become elevated
• causes a slope
• rock cools and becomes more dense
• gravity causes older, denser lithosphere to slide away
• exerts force on plates

Question 9

What 2 types of heat are in the Earth’s core?

Answer 9

• radiogenic and primordial

Question 10

What is the asthenosphere?

Answer 10

the semi-molten layer below the lithosphere, upon which the plates float

Question 11

How does geology provide evidence for continental drift?

Answer 11

Rocks of the same age and type are found where countries would have fitted together

Question 12

Briefly outline how slab pull causes plate movement

Answer 12

• one plate is denser and heavier than the other plate
• subducts beneath less dense plate
• sinking edge exerts a force which continues to pull the subducting plate underneath

Question 13

What is the Benioff zone?

Answer 13

where the lithosphere is passing into the asthenosphere, with friction and heat causing melting of the oceanic plate

Question 14

On what type of plate boundary is the San Andreas Fault found?

Answer 14

Conservative

Question 15

What process(es) form a deep-sea trench?

Answer 15

subduction and downwarping

Question 16

Where are rift valleys found?

Answer 16

continental-continental divergence

Question 17

What is the definition of a magma plume/hot spot?

Answer 17

Areas of high heat flow within the mantle.

Question 18

How do convection currents cause hotspots?

Answer 18

• Convection currents draw heat directly towards a section of the lithosphere
• This section of the crust receives continued and concentrated heat

Question 19

What is meant by the term ‘accretion wedge’?

Answer 19

the build up of material at the point of subduction

Question 20

How do hot spots lead to the formation of island chains?

Answer 20

• concentrated heat on a specific area of the lithosphere
• causes volcanic activity on surface
• plates move whilst hot spots remain stationary

Question 21

What is a concentrated stream of magma called?

Answer 21

magma plume

Question 22

What can cause magma plumes to occur?

Answer 22

radiogenic heat from the core

Question 23

What do magma plumes lead to?

Answer 23

weakness in the crust, which eventually allows magma to force its way through

Question 24

Where are island arcs formed?

Answer 24

oceanic oceanic destructive

Question 25

What are the areas on an oceanic oceanic constructive margin where the plate fractures? Why do they form?

Answer 25

transform faults
plates do not separate in one line

Question 26

What 2 plates are involved in the Great African Rift Valley?

Answer 26

African and Nubian