1a+b- Evidence For Continental Drift + Tectonics

Question 1

What are the 3 main components of earth

Answer 1

Crust
Mantle
Core

Question 2

Describe properties of lithosphere + asthenosphere

Answer 2

Lithosphere = crust + upper solid mantle ( crust - 100km)
- rigid layer
Asthenosphere = below lithosphere (100-300km)
- semi molten

Question 3

Name of super continent and geographer who came up with idea of Continental Drift

Answer 3

• Pangea
• Alfred Wegner
• idea of continents moving apart from super continent 250 million years ago

Question 4

What Previous Geological Evidence was there for Plate tectonics

Answer 4

• Shape pf continents together - evidence for Pangea eg: S America and Africa
• Striations of glaciers evident in Africa and S America ect = shows that continents must’ve been at polar regions once

Question 5

How does palaeomagnetism prove plate tectonics - Recent Evidence

Answer 5

Oceanographers towed magnetometers behind boats
- As plates move apart New land forms
- earths polarity changes every 300,000 years = recorded in new rock formed
- Lava erupting from Constructive margins recorded earths polarity at that time
- strips of rock with same magnetic orientation occur symmetrically either side of ridge = evidence of sea floor spreading

Question 6

How does Sea Floor spreading give evidence for plate tectonics - Recent Evidence

Answer 6

Older Rock found further inland while newer rock found out to sea = Discovered that Rock in Ocean was no more than 200 million years old which is young compared to the continents

Additionally Discovery of large scale Ocean trenches suggesting that Crust was being subducted and destroyed = provided evidence for why earth was not growing despite new land being formed

Question 7

What was Hugo benioffs theory

Answer 7

• the reason the world was not growing despite new land being formed (constructive margins)
• oceanic crust was being destroyed/ melted

-“Benioff zone”

Question 8

Differences between oceanic + continental crust including km of thickness

Answer 8

Oceanic= denser- due to ocean pushing down + compressing
- 6km thick

Continental= less dense= due to high silica content (60%)
-70km thick

Question 9

3 ways plates move

Answer 9

• convection current
• Slab pull
• ridge push

Question 10

Why is the core hot

Answer 10

• heat from collisions with rock when formed
• radioactive decay

Question 11

Mechanism of convection currents

Answer 11

• magma heated by core = particles have more energy + expand= less dense
• less dense mantle rises
• cool down at lithosphere + spread out = move plates
• sinks as cools due to more dense

Question 12

What is the split mantle theory

Answer 12

• 2x sets of convection currents ( 1 in upper 1 in lower mantle)
• reflects the characteristics

Question 13

Ridge push theory

Answer 13

• high land at ridge created as magma cools
• heavy land “pushes” land apart

Question 14

Slab pull theory

Answer 14

• plate subducts
• as plate is “pulled under” next bit is pulled down
• plates are very heavy = drags rest of plate down

Question 15

What is the biggest component of structure of earth

Answer 15

• mantle
  -68%

Question 16

What happens at destructive boundary
(Convergent)

Answer 16

• subduction occurs due to difference in densities
• oceanic plate subducted= deep ocean trench
• earthquakes on Benioff zone= release of seismic energy from friction
• melting of plate = volcanos

Question 17

Why are mantle + inner core solid despite high temp

Answer 17

High pressure stops melting

Question 18

What is required for a volcano

Answer 18

• molten rock

Constructive = magma from mantle
Destructive = magma from melted plate

Question 19

Why does Rock melt at constructive + destructive boundary’s

Answer 19

Constructive= low pressure in gap between plates = rock can melt

Destructive= plate subduction drags down volatiles with it (CO2 + H2O) to asthenosphere

• volatiles lower melting point of rock

Question 20

Properties of basic lava

Answer 20

• divergent/ constructive p boundary
• decompression melting
• asthenosphere melts
• low silica content = low viscosity
• gasses vented easily/ no pressure
• balsatic rock
• very high temp = from mantle
• gentle/ effusive + frequent eruptions
• gently sloping shield volcano

Question 21

Properties of acidic lava

Answer 21

• destructive/ convergent P boundary
• volatiles for melting
• U mantle + crust (asthenosphere, lithosphere, oceanic crust) melt
• high silica content= high viscosity
• gasses trapped until eruption
• Andesitic + Rhyolitic rock
• lower temp for melting
• violent + explosive eruptions
• steep sided + composite volcano

Question 22

What factors effect explosivity of eruptions

Answer 22

• high viscosity of lava = sticky
• cooler temp of magma
• lots of gas bubbles = high pressure

Question 23

What is VEI

Answer 23

Volcanic explovity index
- measures magnitude + speed
Magnitude= how much material
Speed of eruption= intensity

Question 24

Why is there a build up of pressure at destructive boundary’s

Answer 24

• magma must force its way though Lithosphere + crust above = high pressure

Question 25

Why does acidic lava produce composite volcanoes

Answer 25

- sticky lava moves slowly + does not Travel far from volcano - build up of material = composite volcano

Question 26

What happens at a collision boundary

Answer 26

- little difference in density results in no subduction - plates compressed and folded = fold mountains - plates can “grind” together causing earthquakes

Question 27

Why do convection currents move plates

Answer 27

- magma rising up pushes plates apart as convection currents circulate

Question 28

What happens at conservative plate boundary

Answer 28

- plates slide past each other - no subduction = no volcanic activity -friction between rocks = build up of pressure - can leave “tear” in landscape where plates have moved - can affect river course or drainage patterns

Question 29

Why does Thickness of Ocean Layer increase as you move further from constructive plate margin and Why does Oil/Coal in Antarctica show that plates have moved

Answer 29

Cooling of the magma that comes out of the mid-ocean ridge = As it cools, it becomes denser and thicker also accumulation of more sediment on plate showing evidence its been there longer Oil/Coal requires tropical climates and dense vegetation to form = shows its moved

Question 30

Asthenosphere vs Lithosphere

Answer 30

Both part of Upper Mantle Asthenosphere is below lithosphere and is more fluid whereas Lithosphere is above and is made of Crust and Upper most mantle - Rigid

Question 31

Describe a Divergent/Constructive boundary

Answer 31

Magma rising from Lithosphere Forces Plates to move apart as Convection Currents Gap created has lower pressure due to No rock above = Mantle can melt and act as Liquid rising through Gap Mantle rises and is instantly Cooled by Ocean = New land

Question 32

Why can you get earthquakes at Divergent/Constructive margins

Answer 32

Rising magma puts pressure on Dome created by rising magma at C-C , Rocks fracture producing rift valleys = frequent and low energy Es Transform faults formed from moving plates = conservative margins +Es

Question 33

Activity at Hotspots

Answer 33

Hot spot is a particularly Hot section of Mantle = Can Melt through crust causing Volcanic activity Movement of plates transport Volcano and Land form away from Hotspot eg: Hawaii

Question 34

Previous Biological evidence for Plate Tectonics

Answer 34

Similar Fossils of Marine Shellfish/Brachiopods in Australia and Indian Rock = Brachiopods are small shellfish , Unlikely that they would cross large stretch of ocean = Suggests continents were once much closer together - Similar Reptiles/Mesosaurus fossils in S America and S Africa = reptile are freshwater so could not have crossed ocean = Continents must've once been together

Question 35

How Long and tall is the Mid-Atlantic Ridge

Answer 35

1000 miles long and 2500km high

Question 36

How deep is the Mariana Trench

Answer 36

12km

Question 37

Describe how Oceanographers discovered Sea Floor spreading and Palaeomagnetism

Answer 37

Paleomagnetism = Towed Magnometers behind boats Sea Floor spreading = Probed the crust in oceans to discover that it was thicker and Older away from Ridge