Plate Tectonics

Question 1

What’s The Theory of Plate Tectonics?

Answer 1

Plate tectonics states that the earths lithosphere is broken into a number of slabs called plates
These plates float on top of the mantle and are constantly in motion

Question 2

Who proved scientifically the theory of plate tectonics in 1963

Answer 2

Fredrick Vine and Drummond Matthews

Question 3

Earlier theories that helped form the theory of plate tectonics were?

Answer 3

Continental drift, Alfred Wegner in 1912
Conventional currents, Arthur Holmes in 1928
Mid ocean ridges, Maurice Ewing 1947
Sea floor spreading, Harry Ness 1962

Question 4

What is continental drift

Answer 4

Suggests that the continents are constantly moving across the planet by convection currents

Question 5

Who originally discovered the idea of pangea

Answer 5

Wegner

Question 6

Evidence of continental drift

Answer 6

Continental fit, S.america and west coast of Africa fit together. A bit less obvious due to erosion

Matching plant fossils eg fern in s.America and India, Antarctica

Matching animal fossils eg mesosaurus (fresh water) in s.america and Africa

Matching rock folds and mountains of same era in USA and British isles

Matching Glacial deposit materials in Africa and Australia which are currently too hot to have ice fixtures

Question 7

What’s the reason continents have drifted

Answer 7

Convection currents

Question 8

What are convection currents

How do they occur

Answer 8

Magma deep in mantle becomes superheated by 6000* core, magma becomes hotter and rises (heat rises)

When reached upper mantle it cools and becomes semi molten. It then moves laterally (sideways) before sinking again.

As it moves sideways it rubs off lithosphere and moves plates, causing friction

Question 9

What’s slab-pull force

Answer 9

When the edge of a plate begins to sink into a mantle it then pulls the rest of the plate with it (subduction)

Question 10

Which sinks into mantle? Continental or oceanic? Why?

Answer 10

Oceanic is heavier so will sink

Question 11

What happens at a divergent plate boundary

Answer 11

Two plates separate

Question 12

Example of a diverting plate boundary feature

Answer 12

Mid ocean ridge

Question 13

Example of a diverging plate boundary on earth, in terms of which plates

Answer 13

American plate diverging from Eurasian plate to form mid Atlantic ridge

Arabian and African plate are diverging to cause East African Rift Valley

Question 14

How are mid ocean ridges formed and give an example

Answer 14

Convection currents cause plates to pull apart

Magma rises up through gap and cools as it reaches the surface creating new oceanic crust. Plates move further and further apart as new crust forms

Magma that has risen and cooled forms a mid ocean Rigde (mid Atlantic ridge) which is mostly below sea level. But some has risen to form islands such as Iceland

Some magma rises more violently causing volcanic mountains

Question 15

What are transform plates

Answer 15

Plates that are passing by each other either in opposite directions or along side each other but at different speeds

Question 16

Give an example of plates that are transverse

Answer 16

Pacific plate and North American plate at San Andreas fault

Question 17

Give a feature that is at transform plates

Answer 17

Transverse faults

Question 18

Explain the San Andreas fault line

Answer 18

It’s where the North American plate and the Pacific plate move past each other.

Both move in a north western,y direction but at different speeds. Pacific plate moves x6 faster than North American plate. This causes cracks in earths crust. Tension builds up as rocks continue to jam against eachoter before slipping away.

Slips cause plates to jerk releasing shock waves which cause tremors and earthquakes

SAN Francisco is on the fault line so suffered from earthquakes

Question 19

What are convergent plate boundaries

What happens at them

Answer 19

Plates collide

Question 20

Example of converging plates

Answer 20

South American and nazca plate

Question 21

Explain what happens at the south America and nazca plate collision

Answer 21

Heavier nazca plate pushes under South American plate (subduction)

Where oceanic crust descends a deep ocean trench (Peru-chile trench)is formed. Trenches are the deepest parts of our oceans.

Oceanic crust is destroyed and melted in earths mantle. Melted crust material forms batholiths (magma reservoirs), huge underground masses of molten magma. Some magma my make it’s way to the surface to form volcanic mountains

Friction between plates causes underground rock to bend and snap causing earthquakes eg great Chilean earthquake.

South American plate is lighter and buckled up to form fold mountains Andes

As heavier layer sinks, parts if it are scraped off by other plate. Scraped off crust is called terranes and they pile up at the end of fold mountains

Question 22

What is the name for colliding plates

Answer 22

Covering

Question 23

What is the name for separating plates

Answer 23

Divergent

Question 24

What’s the name for passive plates

Answer 24

Transform

Question 25

Example of an oceanic and continual convergent plate

Answer 25

Nazca plate and South American plate form oceanic trench

Question 26

Example of oceanic and oceanic plate converging

Answer 26

Pacific plate and Philippine plate forming Mariana Trench

Question 27

Example of continental and continental plate converging

Answer 27

Indo- Australian and Eurasian plate forming Himalayas

Question 28

Constructive plate boundaries

Answer 28

Divergent (separating)

Constructive as new crust is formed

Question 29

Destructive plate boundaries

Answer 29

Convergent (colliding)

Question 30

Length of mid Atlantic ridge

Answer 30

1500km

Question 31

Example of volcanic mountain on mid Atlantic ridge

Answer 31

Mount Helka

Iceland

Question 32

Length of San Andreas fault

Answer 32

1300km

Question 33

Earthquake example on San Andreas fault

Answer 33

San Francisco 1906

Question 34

Depth of Mariana Trench , worlds largest ocean trench

Answer 34

1100km

Question 35

Plates diverging at East African Rift Valley

Answer 35

African
Arabian
Forming Red Sea

Question 36

Rate East African Rift Valley is widening by

Answer 36

4mm a year