Earth and the crust

Question 1

define lithosphere

Answer 1

the solid layer of crust in which plates are formed

Question 2

define asthenosphere

Answer 2

soft, plastic like rock in the upper mantle, just below the lithosphere

Question 3

what is the thickness of continental crust?

Answer 3

25-70km

Question 4

what is the thickness of oceanic crust?

Answer 4

7-10km

Question 5

what age is continental crust?

Answer 5

2 billion years +

Question 6

what age is oceanic crust?

Answer 6

180-200 million years

Question 7

what is the density of continental crust?

Answer 7

2.7g cm3

Question 8

what is the density of oceanic crust?

Answer 8

2.9g cm3

Question 9

what rock type is continental crust?

Answer 9

granite

Question 10

what rock type is oceanic crust?

Answer 10

basalt

Question 11

what is the mineral content of continental crust?

Answer 11

aluminium, silicon, oxygen

Question 12

what is the mineral content of oceanic crust?

Answer 12

silicon, magnesium and oxygen

Question 13

what is the theory of ‘Paleomagnetism’?

Answer 13

• new material is constantly being produced
• earths magnetism flips back and forth everynow and again which results in a striped rock pattern
• all possible due to ocean floor spreading (mid ocean ridge)
• it is symmetrical on both sides of the ridge
• process called ridge push

Question 14

what is the process in subduction zones called?

Answer 14

• gravity pulls the oceanic plate down in the mantle
• this destroys crust material and keeps the Earth in shape
• this process is called slab pull

Question 15

for a stable earth, what must be equal to what?

Answer 15

ridge push = slab pull

Question 16

what is earth thought to have arisen from?

Answer 16

‘planetesimals’ out of ash cloud, stuck together which produces heat from decay of uranium in core

Question 17

what is the process of movement in the mantle?

Answer 17

• radioactive decay in the core heats material
• heated rock rises as it is less dense
• at the top semi molten rock spreads out, moving plates above with it
• cools and sinks back down to be reheated
• process repeats

Question 18

what is jigsaw fit?

Answer 18

similarities in coastlines (east coast of S. American and west coast of Africa) seem to fit like a jigsaw, suggesting they were once connected.
any gaps in the fit are likely due to erosion

Question 19

what is tectonic evidence?

Answer 19

fragments of old fold mountain belts (400-450 million years old) found spread
pieces of Calodien belt found Greenland, Canada, England, Ireland, Scotland and Scandinavia

Question 20

what is geological fit?

Answer 20

geology of S. America and W. Africa reveal ancient rock outcrop over 200 mill years both consistent on both continents

Question 21

how was the east African ridge produced?

Answer 21

(1) elevated heat flow creates bulges in Kenya and Ethiopia
(2) the brittle crust cracks into faults
(3) convection currents in asthenosphere causes the extension of crust
(3) rift continues to extend, crust becomes thinner and erupts
(4) eventually African plate splits in 2 : Nubian and Somalian

Question 22

what is the benioff zone?

Answer 22

• the further the rock descends, the hotter the surroundings get
• this, along with frictions heat, melts the plate into magma

Question 23

what are the types of destructive boundaries?

Answer 23

oceanic - continental
oceanic - oceanic
continental - continental

Question 24

how do fold mountains?

Answer 24

• oceanic plate is subducted as it is more dense

- material is scraped off the subducting plates and folds up into fold mountains

Question 25

how do mid ocean ridges form?

Answer 25

(1) convection currents in the mantle move plates (2) balsatic lava rises up (3) lava turns into rock (4) layers build up to form ridges

Question 26

what is the process at a constructive plate?

Answer 26

- 2 plates move apart - magma rises up - volcanoes form - rift valleys form

Question 27

what is the process at a destrucive plate?

Answer 27

- oceanic plate goes below less dense continental plate - plate sinks and melts - magma rises through cracks - volcanoes form

Question 28

what is the process at a collisional plate?

Answer 28

- 2 plates of similar density move together - material buckles up - fold mountains form

Question 29

what is the process at a conservative plate?

Answer 29

- 2 plates slide past each other | - where friction builds and slips, major earthquakes occur

Question 30

what is are the three types of hazard?

Answer 30

geophysical (driven by earths own internal energy: volcanoes, seismic activity) atmospheric (driven by processes in the atmosphere: tropical storms) hydrological (driven by water bodies: floods, tsunamis)

Question 31

what are the issues with perceptions of hazards?

Answer 31

- if people are used to the threat of natural hazards, then they perceive the hazard as less of a threat - if people are richer, then they can flee from a hazard, and so the hazard is not as bad to them

Question 32

what is 'fatalism'?

Answer 32

doing nothing can be seen as fatalist, as there is a

Question 33

what is the hazard management cycle?

Answer 33

preparedness response recovery mitigation

Question 34

define prepardness

Answer 34

large scale events can rarely be prevented

Question 35

define reponse

Answer 35

speed of response depends on the effectiveness of plan

Question 36

define recovery

Answer 36

restoring the affected area to something like normality

Question 37

define mitigation

Answer 37

actions aimed at reducing the severity of an event

Question 38

what are the 4 steps on the park model?

Answer 38

pre-disaster relief rehabilitation reconstruction

Question 39

what is the aim of the park model?

Answer 39

to improve quality of life, better than it was before

Question 40

define relief as on the park model

Answer 40

immediate local and possibly global response in form of aid, expertise and search/rescue

Question 41

define rehabilitation as on the park model

Answer 41

a longer phase lasting weeks/months when infrastructure & services are restored

Question 42

define reconstruction as on the park model

Answer 42

restoring to the same, or better, quality of life as before the event. likely to mitigate against a similar level of disruption