Plate Boundaries And Continental Drift

Question 1

Who proposed the theory of continental drift and when?

Answer 1

Alfred Wegener in 1912, worked on his idea until 1930 when he died

Question 2

What is Pangaea and when did Wegener proposed it to exist?

Answer 2

Pangaea is the super continent of all the continents being together. He proposed it to exist in the Carboniferous period 250 million years ago

Question 3

What is palaeomagnetism?

Answer 3

Changes in the polarity. The magnetism of the Earth experiences magnetic reversals every 400,000 to 500,000 years. These are recorded in the solid solidified rocks at constructive margins

Question 4

How is the earths magnetic field shown in the rocks?

Answer 4

The lava holds iron particles and depending on the polarity at the time of formation, it can get locked in the rocks and examined to show the striped pattern.

Question 5

How does sea floor spreading prove continental drift?

Answer 5

Fresh molten rock reaches ocean bed and older rock gets pushed away from the ridge in a ‘conveyor belt’ way. Sea floor spreading moves material across ocean floors, widening it. Plates moved by sea floor spreading from mid-ocean ridges to ocean trench where material gets subducted into the asthenosphere.

Question 6

What did the 1960s ocean drilling programme prove?

Answer 6

Thickest and oldest sediment was found nearest to continents, and no rocks were older than 200 million years, confirming the constant recycling of the crust. Also found a spatial pattern of sediments, supporting sea floor spreading

Question 7

What is the lithosphere?

Answer 7

Rigid outer layer of the earths rocks consisting of the crust and upper mantle. It is the coolest and most rigid part.

Question 8

What is Mohorovičić discontinuity?

Answer 8

The boundary between mantle and crust where there are sudden changes in seismic wave velocities. Indicates transition between rock compositions.

Question 9

Asthenopshere

Answer 9

Located below the crust, portion of the earths mantle that flows like molten plastic. It is involved in plate tectonic movement as convection currents happen here. Semi-molten, hot plastic.

Question 10

What are convection currents?

Answer 10

Occurring within the molten rock, they act as a push force for the tectonic plates. The direction of movement and type of plate margin is determined by which way they flow. Heat rising and falling inside the mantle creates these currents generated by radioactive decay in the core.

Question 11

Explain ridge-push and slab-pull.

Answer 11

Slab pull - subduction zone, force of the dense oceanic plate subducting under the continental plate and pulled by gravity into the mantle. Ridge push - pushing force plates experience when plates move apart.

Question 12

How does palaeomagnetism prove evidence for continental drift?

Answer 12

There is a striped pattern on the ocean floor that begins with lava erupting. This lava contains iron particles and once erupted, they lock into the igneous rocks so the magnetic orientation is locked in depending on the polarity at that time. this shows continental drift because symmetrical patterns are created which pushes older rock away by sea floor spreading

Question 13

How do the ages of sea floor rocks prove continental drift?

Answer 13

The oldest rocks in the ocean are only 200 million years old. The magma that erupts at a divergent plate boundary creates new rock that is destroyed after continuous formations as it reaches subduction at ocean trenches/convergent plate boundary. These rock movements on the ocean floor can explain continental drift.

Question 14

What are the processes on a divergent plate boundary?

Answer 14

The two lithospheric plates move apart by convection currents which form in the asthenosphere, driven by heat from radioactive decay in the core. Two plates move apart forming new land.

Question 15

What are transform faults?

Answer 15

Where the mid-ocean ridges are displaced, fault lines are created which transmit earthquakes as seismic waves travel along it as the blocks split.

Question 16

What are undersea mountains known as?

Answer 16

Mid-ocean ridges

Question 17

What is a rift valley? Give an example.

Answer 17

A narrow zone that is a developing divergent plate boundary where the plate is splitting into two tectonic plates. As it continues, a new ocean basin will form. Am example is the Red Sea that is filled with water. There is also one forming in east Africa where the Somali plate and Nubian plate are formed by the breaking of the African plate.

Question 18

Describe what happens at an oceanic-continental convergent plate boundary.

Answer 18

The denser oceanic plate is submerged beneath the continental plate and breaks off into the asthenosphere to be recycled in magma. This forms a deep trench and volcanoes and fold mountains on the continental plate. The sub ducting plate creates large collections of magma called plutons that rises to be erupted from volcanoes.

Question 19

Describe what happens at an oceanic-oceanic convergent plate boundary.

Answer 19

Two oceanic plates collide and the older one with higher density is likely to subduct. As a result, it is forced deeper into the mantle and begins to melt. Magma chambers are produced that break the surface as a volcanic eruption. A feature is a volcanic island arc and many of these in a chain next to a trench creates an island arc.
Plutons are formed that are pockets of magma deep underground that intrude into igneous rock as they didn’t make it to the surface.

Question 20

What happens at a continental-continental divergent plate boundary?

Answer 20

Two continental plates converge to form landforms such as fold mountains, fault lines, high plateaus. Neither plate can subduct because they are both very thick. This means magma cannot get through so there are no volcanoes. Fold mountains are formed as the rocks are folded upwards.

Question 21

Conservative plate boundary

Answer 21

Two tectonic plates sliding past each other. If they get stuck, pressure builds up and releases as earthquakes. The features are narrow ridges which are long pieces of highland, sag ponds and strike slip faults.

Question 22

What was the first piece of evidence on continental drift that failed to provide a significant explanation on the movement of continents?

Answer 22

The apparent bit of the continents where the coastline is appeared to fit together like a puzzle.

Question 23

What is the theory of continental drift?

Answer 23

The continents are mobile and have moved through time. the supercontinent Pangaea has been broken up.

Question 24

What are fossils?

Answer 24

Preserved traces of plants and animals that are found in rock

Question 25

Describe seafloor spreading

Answer 25

The symmetrical pattern of magnetic orientation either side of mid ocean ridges indicate that fresh molten rock from the asthenosphere reaches the ocean bed, pushing older rock away. This moves material across ocean floor as a ‘conveyor belt’ and eventually the rock reaches an ocean trench where subduction occurs.

Question 26

What is subduction?

Answer 26

Material is pushed down with force into the asthenosphere and becomes semi-molten.

Question 27

Give examples of fossil correlations

Answer 27

•similar fossil reptiles found in S. America and S.Africa
•similar brachiopods (marine shellfish) found in Australia and Indian limestones
•fossils from younger rocks than the Carboniferous period in Australia and India show fewer similarities suggesting they followed different evolutionary pathways.

Question 28

Explain rock and mountain correlation for supporting the theory of continental drift

Answer 28

Identical mountain structures, rock and age, found on either sides of the ocean. For example eastern North America and Northern Europe
Theory of continental drift is that continents on mobile and have moved through time

Question 29

Explain how cold and glacial evidence can prove continental drift

Answer 29

Coal has been found in current colder regions suggesting they were once in tropical regions. Glacial striations, ice marks on rock, have been found in now tropical regions on the equator meaning they were once near the poles in colder environments before continental drift moved them to the opposite climate.

Question 30

What is sea floor spreading?

Answer 30

The process that oceanic plates split apart and new crust is formed through the rising of balsatic magma

Question 31

What is the difference between a convergent and divergent plate boundary?

Answer 31

Convergent = two plates collide, destroying land. The denser oceanic plate is subducted below the lighter plate and melted in the asthenosphere.
Divergent = two plates pull apart, creating new land.

Question 32

Compare the outer core and inner core

Answer 32

Outer core is around 4000 degrees Celsius where is inner core is hotter at 6000°C. The outer core is liquid iron and nickel but the inner core is solid nickel and iron because of the pressure from the other layers.

Question 33

What are the features on a divergent plate boundary? (Plates move apart)

Answer 33

Ocean ridges - the upwelling of magma forms a ridge e.g mid Atlantic ridge (ocean)
Transform faults - ocean ridges are broken into segments. Where the ridges are displaced for lines are created with transmit earthquakes as the blocks slip. (Ocean)
Pillow lavas - eruption of lava underwater cools quickly into rounded mountains on the sea bed. (Ocean)
Rift valleys - divergent plate boundaries on land create a valley at the surface as plates crack and rock blocks fall downwards. (Land)