Eduqas GCSE Geology · 2.2

Plate Tectonics

50 revision questions with answers for 2.2 Plate Tectonics in Eduqas GCSE Geology (spec C480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, Five Degrees, Associations, or read every question and answer below. Not official Eduqas material.

All 50 questions and answers

Question 1
What are Earth's three main compositional layers?
Answer:
Crust, mantle and core.
Question 2
What is the lithosphere?
Answer:
The cold, rigid outer shell comprising the crust and uppermost mantle.
Question 3
What is the asthenosphere?
Answer:
A weaker region of the upper mantle beneath the lithosphere that can deform and flow slowly.
Question 4
How is the lithosphere divided?
Answer:
Into rigid tectonic plates that move relative to one another.
Question 5
Is the asthenosphere simply a global ocean of liquid magma?
Answer:
No. It is predominantly solid rock that can deform slowly; limited partial melt may occur in places.
Question 6
How do the lithosphere and crust differ?
Answer:
The crust is a compositional layer; the lithosphere is a mechanical layer containing crust and uppermost mantle.
Question 7
How do plate boundaries relate to earthquakes and volcanoes?
Answer:
Many earthquakes and volcanoes cluster at or near plate boundaries, although some occur within plates.
Question 8
Who proposed continental drift in 1915?
Answer:
Alfred Wegener.
Question 9
How does continental shape support former continental joining?
Answer:
The margins of South America and Africa fit approximately together, especially when continental shelves are considered.
Question 10
How can matching fossils support continental drift?
Answer:
The same fossils on now-separated continents can indicate that the land areas were once joined.
Question 11
How can matching rock sequences support continental drift?
Answer:
Rock belts of similar age and type on opposite sides of an ocean can be correlated across a former join.
Question 12
Why was Wegener's original explanation debated?
Answer:
He lacked a convincing mechanism that could move continents through or with the ocean floor.
Question 13
What is sea-floor spreading?
Answer:
Formation of new oceanic lithosphere at a ridge and movement of older ocean floor away from it.
Question 14
Who proposed sea-floor spreading in 1960?
Answer:
Harry Hess.
Question 15
What did Vine and Matthews use to support sea-floor spreading?
Answer:
Symmetrical magnetic stripes in oceanic rocks on either side of a ridge.
Question 16
How are magnetic stripes produced?
Answer:
Iron-bearing minerals record Earth's magnetic polarity as basalt cools; reversals and spreading create alternating bands.
Question 17
Describe the typical pattern of magnetic stripes around a ridge.
Answer:
Bands of alternating polarity run approximately parallel to the ridge and form a broadly symmetrical pattern.
Question 18
What is the age pattern of ocean crust away from a spreading ridge?
Answer:
It is generally youngest at the ridge and progressively older farther away on either side.
Question 19
Why is heat flow generally high at an ocean ridge?
Answer:
Hot mantle and newly formed crust lie close to the surface beneath the ridge.
Question 20
Why can magnetic stripes be offset along a ridge?
Answer:
Transform faults can displace segments of the ridge and their associated stripe patterns.
Question 21
Ocean crust 100 km from a ridge formed 5 million years ago. Calculate the average one-sided rate.
Answer:
100 km / 5 Ma = 20 km per million years = 2 cm per year.
Question 22
Two points are 160 km apart and separated over 4 million years. Calculate their average relative rate.
Answer:
160 / 4 = 40 km per million years = 4 cm per year.
Question 23
Why must you distinguish one-sided spreading from total separation rate?
Answer:
Total separation includes motion on both sides; a one-sided rate measures distance from the ridge to one plate.
Question 24
How do GPS data support plate tectonics?
Answer:
Repeated positions show the direction and rate at which locations on plates move today.
Question 25
What happens at a divergent plate boundary?
Answer:
Plates move apart, allowing mantle to rise and new oceanic lithosphere to form.
Question 26
How does basaltic magma form beneath a spreading ridge?
Answer:
Rising upper mantle undergoes partial melting as pressure decreases.
Question 27
Give an example of a divergent boundary.
Answer:
The Mid-Atlantic Ridge.
Question 28
Name two landforms associated with sea-floor spreading.
Answer:
An ocean ridge and a central rift valley; abyssal plains occur farther from the ridge.
Question 29
What is an abyssal plain?
Answer:
A broad, relatively flat region of deep ocean floor, generally away from the elevated ridge.
Question 30
What happens at a conservative plate boundary?
Answer:
Plates slide past one another; lithosphere is neither created nor destroyed at the boundary.
Question 31
Why do conservative boundaries produce earthquakes?
Answer:
Plates can lock due to friction, then slip suddenly and release stored energy.
Question 32
Give an example of a conservative plate boundary.
Answer:
The San Andreas fault zone in California.
Question 33
Is subduction typical of a conservative boundary?
Answer:
No. The main relative motion is lateral sliding.
Question 34
What happens at an oceanic-continental convergent boundary?
Answer:
Denser oceanic lithosphere subducts beneath continental lithosphere, producing a trench, earthquakes and often volcanoes.
Question 35
What is a Benioff zone?
Answer:
A dipping zone of earthquake foci that traces the descending slab at a subduction boundary.
Question 36
What magmas are associated with oceanic-continental convergence in the specification?
Answer:
Andesitic and granitic magmas can form through partial melting in the subduction setting.
Question 37
Give an example of an oceanic-continental convergent margin.
Answer:
The Andes on the western margin of South America.
Question 38
What features commonly form at oceanic-oceanic convergence?
Answer:
A deep ocean trench and a volcanic island arc.
Question 39
What features commonly form when two continents converge?
Answer:
High mountain belts, folding, thrust faults and regional metamorphism; crustal partial melting can produce granite.
Question 40
Give an example of continental collision.
Answer:
The Himalaya, formed by convergence of the Indian and Eurasian plates.
Question 41
Why is an ocean trench commonly associated with subduction?
Answer:
The descending oceanic plate bends downward at the surface, forming a deep depression.
Question 42
A dipping band of earthquakes extends beneath a continent. What boundary is suggested?
Answer:
A convergent subduction boundary, because the dipping foci mark the descending slab.
Question 43
Why is plate theory continually tested?
Answer:
New observations can confirm, refine or challenge models of how plate processes operate.
Question 44
What is seismic tomography used for?
Answer:
It uses seismic-wave data to build images of variations within Earth and investigate structures such as slabs.
Question 45
How can ocean drilling test models of oceanic crust?
Answer:
Recovered rocks allow geologists to compare actual crustal composition and sequence with predictions.
Question 46
Why is a single earthquake not enough to map a whole plate boundary?
Answer:
Many events and their locations, depths and other evidence are needed to identify a reliable pattern.
Question 47
An ocean ridge shows high heat flow and young basalt. What boundary is likely?
Answer:
A divergent boundary where new ocean crust forms.
Question 48
A mountain belt has folded strata and thrust faults. What stress is indicated?
Answer:
Compression, consistent with a convergent plate setting.
Question 49
How do earthquake depths differ at a subduction zone and a typical spreading ridge?
Answer:
Subduction earthquakes can deepen along a dipping slab; ridge earthquakes are generally shallow.
Question 50
Give two independent observations supporting sea-floor spreading.
Answer:
Symmetrical magnetic stripes and increasing ocean-floor age away from a ridge.

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