Plate Movement

Question 1

Describe the core of the earth

Answer 1

Size of Mars 
Densest part of the planet 
Rocks rich in nickel and iron 
Two parts : semi molten outer core and a solid inner core 
Temperature 5000c

Question 2

Describe the mantle of the earth

Answer 2

Surrounds core 
Mainly silicate rocks rich in iron and magnesium
Most is semi molten 
Up to 3800c 
Densities increase as you go down mantle

Question 3

Describe the crust of the earth

Answer 3

Thinnest layer, coolest, less dense rock

Rich in silicon, oxygen, aliminium, potassium and sodium

Question 4

What are the two types of crust

Answer 4

Oceanic crust

Continental crust

Question 5

What’s oceanic crust

Answer 5

Thin layer, younger basalt rock known as sima ( Silica and magnesium)
Thickness - 5-10km

Question 6

What’s continental crust

Answer 6

Thicker layer of older, lighter granite rocks (sial ( silica and aluminium) crust up to 70km thick

Question 7

What’s Alfred wegeners theory (1912)

Answer 7

All continents were once joined in ancient supercontinent Pangea. At some point the land masses had drifted apart until they occupied their current position

Question 8

Evidence for wegeners theory of continental drift

Answer 8

• continental or jigsaw fit
• geological evidence
  -climatological evidence
  Biological evidence

Question 9

What is the continental or jigsaw fit evidence

Answer 9

Some continents seem to fit together if placed beside each other eg Africa and South America

Question 10

What’s the geological evidence for wegeners theory

Answer 10

Rocks of the same age and type and formation found in SE Brazil and South Africa
Similar glacial deposits found in Antarctica and South America and India ( thousands of km apart )

Question 11

What’s the climatological evidence for wegeners theory

Answer 11

Places as far apart as Antarctica,North America and the U.K. contain coal deposits of a similar age that were formed in tropical conditions. They are no longer in tropical conditions so must have drifted apart

Question 12

What’s the biological evidence for wegeners theory

Answer 12

Similar fossil formations are found either side of the Atlantic.
Plant remains from humid swamps that later formed coal deposits have been found in India and Antarctica

Question 13

What did Harry Hess do ( sea floor spreading)

Answer 13

Updated wegeners ideas. Examined crust either side of mid Atlantic ridge
Studied age of rocks on Atlantic Ocean floor he found the youngest in the middle and oldest nearest USA. New rocks still been formed in Iceland

Question 14

Evidence for sea floor spreading

Answer 14

Look at crust either side of mid Atlantic ridge

Palaeomagnatism

Question 15

What is palaeomagnatism - evidence of sea floor spreading

Answer 15

Study of changes in earths magnetic field (polarity. Earths magnetic field switches polarity.iron records record magnetic field. Rocks in ocean crust show alternating polarity.,magnetic stripes are mirrored across ridge suggest ocean crust spreading

Question 16

What are convection currents

Answer 16

Slow moving thermal currents Hotspots heat lower mantle creating thermal currents rise and sink. This circulation of magma allows plates to move.

Question 17

Sea floor spreading means more crust is created so earth would get bigger? But it didn’t, why??

Answer 17

Parts of earths crust were being destroyed. On Pacific coast submarines found deep ocean trenches which were destroying crust as new crust was created. It did this by subduction and provided mechanism for drifting of continents

Question 18

Why are oceanic plates younger than continental

Answer 18

They are denser so can sink therefore are destroyed at ocean trenches and are continuously being formed at ocean ridges.
Continental plates won’t sink due to low density

Question 19

What is a constructive plate margin

Answer 19

Where two sections of crust move apart
Can be two sections of oceanic crust
Or oceanic and continental crust

Question 20

Process that happens at constructive margin with two oceanic plates

Answer 20

Crust weakens and cracks and magma pushed through gaps it cools and solidifies and forms submarine volcanoes. The pulling apart can form faults

Question 21

Process that occurs at constructive margin between oceanic and continental crust

Answer 21

Only occurs where there’s a convection cell . Continental crust heated by cell.over time crust cracks (vertical faults) and moves apart

Question 22

Landforms that happen in oceanic areas where plates move apart

Answer 22

Mid Oceanic ridges eg mid Atlantic ridge overall they have a total length of 60,000km on planet.
Transform faults cut along ridge,Middle of ridge forms deep valley
Underwater volcanoes erupt along mid ocean ridges.

Question 23

Landforms that can happen at constructive plate margins when oceanic and continental plates drift

Answer 23

Rift Valleys. Formed when lithosphere stretches causing it to fracture into sets of parallel faults.land between faults then collapses into deep wide value eg great African Rift Valley extends 4000km from Mozambique to Red Sea. Magma rise though gaps-volcano

Question 24

What happens at a destructive margin,what types are there

Answer 24

Two sections of crust move towards each other, can be:

• oceanic -continental
• continental -continental
• oceanic -oceanic

Question 25

What happens at a destructive oceanic/continental margin

Answer 25

Deep sea trenches eg Peru-chile trench +8km deep
fold mountains ,
volcanoes,
earthquakes

Question 26

Landforms at destructive continental /continental margin

Answer 26

No volcanoes
Earthquakes can happen
Fold mountains eg the Himalayas

Question 27

Landforms at destructive oceanic / oceanic margin

Answer 27

Deep sea trenches - denser of two plates subducts
Earthquakes can be triggered and volcanic eruptions can take place underwater and create island arcs when submarine volcanoes emerge above water eg Mariana islands.

Question 28

How do island arcs form

Answer 28

Two oceanic plates converge ocean trench forms.volcano forms and lava piles up on ocean floor until a submarine volcano rises above sea level to form island volcano. Typically strung out in curved chains - island arcs

Question 29

How does magma that forms island arcs form

Answer 29

Produced by partial melting of defending plate in subduction and or overlying lithosphere

Question 30

What is a conservative plate margin eg San Andreas fault system

Answer 30

Where two plates slide past each other. Pressure builds up as they rub and jolts. Can cause faults and earthquakes. One plate can move faster than the other
Eg Christchurch earthquake 2011

Question 31

How do fold mountains form at destructive continental/continental margins eg the ALPS

Answer 31

Continental plates crust is Lower density so not much subduction. As plates move towards each other edges and sediment between them forced up into fold mountains. Movement of plates trigger shallow focus earthquakes. Material can also be forced downwards

Question 32

What are hotspots

Answer 32

Localised area of concentrated radioactive elements inside the mantle they occur at Hawaiian islands
Don’t occur at plate boundaries

Question 33

What happens at a hotspot

Answer 33

A plume of magma can rise and eat into plate above.where lava breaks through surface it cools and solidifies over time and active volcanoes can occur above hotspots

Question 34

Landforms that occur at hotspots

Answer 34

Hotspots are stationary and as Pacific plates move over it a line of volcanoes is created called and island chain.volcano above hotspot is active and others extinct. Seeing the age of volcanoes in a line supports Alfred wegners plate movement theory .

Question 35

What will happen over a very long period of time to old Volcanoes in island chains et Hawaiian islands

Answer 35

Pressure on crust and marine erosion extinct volcanoes will eventually sink below sea level