Plate Tectonics 1

Question 1

Define MOHO (Mohoronicic Discontinuity)

Answer 1

Boundary between the crust and the mantle

Question 2

Define Sima

Answer 2

Oceanic crust - Silicona nd magnesium

Question 3

Define Sial -

Answer 3

Continental crust - Silicon and aluminium

Question 4

Define asthenosphere

Answer 4

Highly vicious, mechanically weak region of the upper mantle

Question 5

Define geoid

Answer 5

Imperfect sphere. Bulges around the centre and narrows at the poles

Question 6

Give the 4 layers of the Earth

Answer 6

Crust
Mantle
Outer core
Inner core

Question 7

Give the key characteristics of the crust

Answer 7

Thinnest - between 0-20km on avergae

Composed of continental and oceanic crust

Question 8

Give the key characteristics of the Mantle

Answer 8

Thickest section of the Earth at 2900km and makes up 84% of its volume

Made up of iron, silica and magnesium

Over 3000ºC on average

Question 9

Give the key characteristics of the Outer core

Answer 9

The inner core is so hot that it causes this lyer to melt and become liquid.

Made up of iron and nickle

Reaches tempatures of 4000-5000ºC

This layer moves around the inner core and creates the Eath’s magnetic field

Question 10

Give the key characteristics of the inner core

Answer 10

Tempatures can exceed 6000ºC

Mainly irona nd nickle - silid dense ball of metal

Engine and internal enegy source of the rocks

Question 11

Give the key characteristics of the continental crust

Answer 11

Made up of silicon and aluminium

20-30km thick on average

Located on contents and areas close to the shore (continental shelves)

Question 12

Give the key characteristics of the oceanic crust

Answer 12

Made up of silicon and magnesium

Thinner than continental (between 5-10km)

Much denser

Under oceans - formed via sea-floor spreading at mid-ocean ridges

Question 13

Why is oceanic crust newer than continental

Answer 13

O = constantly being created and destroyed whereas can’t happen so easily with continental

Oceanic can be subducted because its more dense tahn its sorounding area so can be subducted and destryed. Created where sea floor spreads. COntinetal is not dense enough

Question 14

Give 3 reasons why the inner core is so hot

Answer 14

Heat from when the planet formed and accreted, which has not yet been lost (Big Bang)

Frictional heating caused by denser core material sinking to the center of the planet

Heat from the decay of radioactive elements

Question 15

Give the 5 pioneers of plate tectoinics

Answer 15

Alfred Wenger

Harry Hess

Fredrick Vine and Drummond Mathews

John Tuzo-Wilson

Dan Mckenzie

Question 16

Who was Alfred Wenger

Answer 16

German metreologist

Published ‘The Origin of Continents and Oceans’ in 1915, which outlined his theory if cintinental drift

Continental drift theory met by sceptism by lots of scientists

Although he had lots of evidence to support his thoey, he lacked the mechanics on how the plates moved

Question 17

Give the 5 lines of evidence

Answer 17

Fossil

Jigsaw

Geological

Glacial

Tectonic

Question 18

Explain fossil evidence

Answer 18

Many examples of fossils found on seperate continents suggesting they were once joined together

If continental drift hadn’t occured then it woudl cntradct darwin’s theory of evolution

Fossils of Mesocrus and Lystceterous found on South Africa, India and Antarctica suggesting the continents were joined

Question 19

Explain tectonic evidence

Answer 19

Fragments of an old fold mountain belt 450 million yers ago are found on widely seperate continents

When these land masses are re-assembled, the mountain belt forms a continious linear feature

Question 20

Explain jigsaw evidence

Answer 20

Any areas where the coast may overlap or leave gaops can be exaplined by costal erosion/deposition and change in sea/land level

Question 21

Explain geological fi evidence

Answer 21

When the geology of eastern South America and West AFrica were mapped, it revealled that ancient outcrops over 200m years ago were continious from one continent to the other

Question 22

Explain glacial evidence

Answer 22

Today, glaciar deposits from the Permo-Carboniferous period are found in Antarctica, South America, India and Australia

If the continents hadn’t moved then it would suggest an ice sheet extending from the southpole to the equator which is unlikely seeing as the UK was near the equator at that point and showns no evidence of such galiac deposits

Question 23

Who was Harry Hammon Hess

Answer 23

Professor of geology at Princeton uni (USA)

Served in the navy in WWII - equiping him with usefull knowlwdge of sonar

Question 24

What book did Hammond Hess publish in 1962

Answer 24

The History of Ociean Basins - outlined how continental drift worked

Late rbecame known as “sea floor spreading”

Question 25

Explain the sea floor spreading theory

Answer 25

Oceans were shallower in the middle and identified the presence of Mid Ocean Ridges rising as a high as 1.5km

In addition found that the deepest parts of the ocean trenches were found very close to the continental margins in the pacific

Hess believed that oceans grew from their centres from molten material escaping the mantle along the ridges. This created new seafloor which then spread away form the ridge in both directions

The ocean ridge was thermally expanded and consequently higher than the ocean floor further away.
As spreading continued, the older ocean floor cooled, became more dense and eventually subjected at a deep ocean trench

Question 26

Give a limmitation to Hess

Answer 26

Hess believed that ocean trenches were the locations where ocean floor was destroyed and recycled - However didn’t have enough evidence to prove it

Couldn’t explain Hawii

Question 27

Describe the work of Vine and Mathews

Answer 27

British geologists - their work looked at the patterns of magnetic striopes in the sea floor.

Confirmed Hess’ theory

Question 28

How does magnetic stripes work

Answer 28

When the material from the mantle rises up through mid-ocean ridges and cools, it preserves a record of the Earth’s magnetic field.

This is because the magnetite in the basalts is strongly magnetic, and aligns with the field when it cools

Question 29

What was Frederick Vine’s and Drummond Mathew’s theory

Answer 29

Hess lacked the evidence to assert that oceanic plates were created at Mid Ocean Ridges

When basaltic lava cools on the sea floor, individual minerals separate - especially iron - and these minerals then align themselves on the sea floor in the direction of the magnetic pole

Earth’s magnetic field swaps direction at points throughout time

Noticed there was a symmetrical pattern of magnetic stripes on either side of the mid ocean ridges. In addition when the basalts of the sea floor were dated, they were found to be the same age at similar distances away from the ridge on each side.

This suggested that the ocean floor was created at the mid ocean ridges, then was split in half by later activity and pushed sideways.

Question 30

How did Vine and Mathews publish their theory

Answer 30

1963, in a paper called ‘magnetic anomomlies over oceanic ridges’.

Became the first scientiic test for sea floor spreading

But still didn’t explain Hawii

Question 31

Why is Hawii an anomolie

Answer 31

Most volcanic activity is found at locations of sea floor spreading (Hess) or subduction zones.

Some volcanic locations such as Hawaii are far away from any known sea floor spreading location or subduction zone.

Question 32

Who is John Tuzo-Wilson

Answer 32

Continental drift theories were accumulating without any explanation for land masses such as Hawii

In 1963, Tuzo-Wilson proposed that plates may move over fixed hotspots in the mantle to create a string of volcanic islands

Hawaii is composed of 19 volcanic islands.

Question 33

What are hotspots

Answer 33

Radioactive decay in the Earth’s core generates hot temperatures.
If the decay is concentrated, hotspots will form around the core

Heat the lower mantle creating localised thermal currents where magma plumes rise vertically

Burn through the lithosphere to create volcanic activity on the surface

Hotspot remains staionary, the movement of the overlying plate reults in formation of a chain of active volcanoes. Hawii

As oceanic lithosphere oves away, volcanic activity ceases, cools and becomes an island

Question 34

Other than hotspots, what did Wilson also discover

Answer 34

Conservative plate boundries

Plates move transversely – causes earthquakes but no volcanoes, without destroying or creating any oceanic crust

Question 35

Who was Dan Mckenzie

Answer 35

There was lots of evidence about continental drift but now evidence to prove why it was happening

Heard Fredrick Vine speak about sea florr spreading and magnetic anomolies

Question 36

What was Mckenzie’s theory - Mantle Convection Hypothesis

Answer 36

He suggested there are two layers in the mantle, each of which are in motion, controlling the movement and behaviour of the tectonic plates above.

Convection currents in the mantle occur when the hot + less dense magma in mantle rises, cools and sinks becuase it is more dense. This repeast in a cyclical motion forming convection currents

Destructive - convection currents force the continental and oceanic plate together. Oeceanic more dense so subducts

Constructive - two plates are forced apart by convection currents forning a gap between the plates

Question 37

Give a limmitation to Mckenzie’s theory

Answer 37

Mantle convection being resposnible for the movent of tectonic olates is now largely out of favour, with modern imagaing techniques unable to identify convection cells in the mantle sufficientley large to drive plate movement

Question 38

What is the most recent theory on plate movements

Answer 38

Gravitational sliding

Question 39

What is gravitational sliding

Answer 39

Combination of ridge push and slab pull

Question 40

What is ridge push (Gravitational sliding)

Answer 40

Takes place with plate movement driven because of the higher elevation of plates at ocean ridges.

As fresh magma wells up at mid-ocean ridges to form new young, oceanic lithosphere, a higher elevation is formed at spreading ridges.

The new oceanic crust gradually cools, gets denser and thickens with age and is pushed ‘downhill’ by gravity as new magma emerges from the active zone of divergence behind it (and thus adds distance from the ridge).

Question 41

What is slab pull

Answer 41

More significant gravitational force acting on the plates

Occurs at destructive plate margins where an oceanic plate subducts under a continental plate, working in tandem with convection currents and gravity

Due to the extreme density and mass, the subducting plate pulls with it the rock behind and forces it to move along as it subducts