1. Plate Tectonics & 2. Plate Boundaries

Question 1

Inner Core

Answer 1

• Solid
• 90% iron, some nickel and sulphur
• 1220km thick
• 5,500 degrees

Question 2

The outer core

Answer 2

• Fluid, molten
• Iron and nickel
• 2,400 km thick
• 3,000-4,000 degrees

Question 3

The upper mantle

Answer 3

• Just beneath crust
• 410km deep
• Mostly solid rock, but some areas are molten
• Divided into the lithosphere and asthenosphere

Question 4

Lithosphere

Answer 4

• The lithosphere included the crust and the brittle upper portion of the mantle
• Rigid
• 5-2000km in depth
• Consists of the plates

Question 5

Asthenosphere

Answer 5

• Denser and weaker layer below the lithosphere
• 100-200km deep
• Temperature and pressure is so high that the rocks are semi-molten and more ductile

Question 6

Ductile

Answer 6

The ability to bend or deform without fracturing

Question 7

The lower mantle

Answer 7

• 600-2700km in depth
• Hotter and denser than upper mantle
• Less ductile
• Solid rock

Question 8

Moho line

Answer 8

The division between the crust and mantle

Question 9

The crust

Answer 9

• Outermost layer of Earth’s structure
• 1% of Earth’s mass
• Solid rocks and minerals
• Oceanic and continental crust

Question 10

Oceanic crust

Answer 10

• Thin (5-10km)
• Denser/ heavier
• Basalt rock
• Sima (silica and magnesium)

Question 11

Continental crust

Answer 11

• Thick (up to 70km)
• Less dense/ lighter
• Granite
• Sial (silica and aluminium)

Question 12

Who discovered continental drift?

Answer 12

Alfred Wegner 1912

Question 13

Who discovered continental drift?

Answer 13

Alfred Wegner 1912

Question 14

Who discovered convection currents?

Answer 14

Arthur Holmes 1928

Question 15

Who discovered mid-ocean ridges?

Answer 15

Maurice Ewing 1947

Question 16

Who discovered sea-floor spreading?

Answer 16

Harry Hess 1962

Question 17

What is the theory of continental drift?

Answer 17

• Suggests the plates were constantly moving by convection currents
• Wegner proposed there was once a supercontinent, known as Pangaea
• Approx. 200 million years ago Pangaea began to break apart

Question 18

What evidence exists in favour of continental drift?

Answer 18

• Continental fit
• Matching Plant fossils
• Matching Animal Fossils
• Matching rock folds and mountains (Appalachians and Caledonians)
• Glacial Deposits (in Africa and Australia are too hot)

Question 19

What is the theory of convection currents?

Answer 19

• Wegner died before being able to prove continental drift
• Holmes suggests that magma deep in the mantle becomes superheated by the 6000 degree core.
• As the magma becomes hotter, it rises towards the crust
• Upon reaching the mantle it becomes semi-molten, then moves laterally before sinking again.
• As it moves sideways it rubs off the lithosphere which leads to the plates separating, colliding and sliding past each other.

Question 20

What is the theory of mid ocean ridges?

Answer 20

• Maurice Ewing discovered a chain of underwater volcanoes and mountains in the Atlantic
• He also discovered that the ocean floor is made of basalt and is thinner closer to the ridge

Question 21

What is the theory of sea-floor spreading?

Answer 21

• Harry Hess added to discoveries made by Ewing, by discovering mid-ocean ridges is where new sea floor was made
• Magma pushed up through the separating plates hardens and creates new ocean floor
• The Atlantic began to open 130 mya and still is

Question 22

What evidence exists supporting sea-floor spreading?

Answer 22

Age of the sea floor- Progressively older the further from the ridge. 10 mya beside ridge, 130 mya near continents

Ocean Sediments- Ocean floor further away from ridge has thicker sediment

Question 23

What are the evolving theories of plate tectonics?

Answer 23

Slab pull, Ridge push, Mantle Plumes

Question 24

What is slab pull?

Answer 24

• Negative buoyancy of a plate causes subduction
• As a plate becomes negatively buoyant, the plate cools and begins to subduct under the less dense plate
• The stress is moved up through the lithosphere, pulling it along the surface by slab pull

Question 25

What is ridge push?

Answer 25

• Mid-ocean ridges form as tension forces at divergent plate boundaries
• Tension forces are caused by plates separating, as plates become thin, cracks or fissures can form. Hot mantle rock will flow up to fill the space.
• As the mantle Rick rises, it reduces in pressure. The melting of the mantle turns it into magma. This magma injects into the plate, cools and becomes new crust
• This pushes the ridge apart by ridge push.

Question 26

What are mantle plumes?

Answer 26

• A mantle plume is a large column of hot rock that rises through the mantle
• The heat from the plume causes rock in the lithosphere to melt, this results in magma chambers
• When these plumes reach the crust, they form diapirs (also known as hot spots) e.g. volcanic islands like the Canary Islands and Hawaii.

Question 27

What are convergent/ destructive plate boundaries?

Answer 27

Two plates colliding

Question 28

What are divergent/ constructive plate boundaries?

Answer 28

Two plates separating

Question 29

What are transform/ passive plate boundaries?

Answer 29

Two plates sliding past each other

Question 30

What are endogenic forces?

Answer 30

Endogenic forces are internal forces within the earth that effect landscape on earth’s surface