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A-level Physical Yr1 > 3.1 Plate tectonics > Flashcards

3.1 Plate tectonics Flashcards

1
Q

What are the different layers of the Earth?

A

Inner Core
Outer Core
Mantle
Asthenosphere
Lithosphere
Crust (oceanic and continental)

In Our Minds Are Little Characters

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2
Q

What is the inner core?

A
  • solid
  • iron/nickel
  • very hot due to pressure/radioactive decay
  • this heat responsible for Earth’s internal energy
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3
Q

What is the outer core?

A
  • semi-molten
  • iron/nickel
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4
Q

What is the mantle?

A
  • mainly solid rock, high in silicon
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5
Q

What is the asthenosphere?

A
  • semi-molten layer
    -allows convection currents to occur
  • this layer is responsible for the movement of tectonic plates
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6
Q

What is the lithosphere?

A
  • broken up into plates
  • madeup of brittle crust and top part of the upper mantle
  • coolest/most rigid part of the Earth
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7
Q

What is continental crust?

A
  • solid rock (granite)
  • older, thicker rocks
  • LESS DENSE
  • CANNOT sink/be destroyed
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8
Q

What is oceanic crust?

A
  • solid rock (basalt)
  • younger/created at constructive plate margins
  • denser but thinner
  • can sink and be destroyed at subduction zone
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9
Q

How do tectonic plates move?

A
  • Alfred Wegner first to suggest continents drifted but could not account for how
  • lots of evidence to prove they shifted location but wasn’t until discovery of ocean rides that people believed him
  • in 1930s able to explain how plates were moving: CONVECTION
  • core’s temp around 6000C**, causes **magma to rise in the mantle, as it reaches the top of the mantle it cools to around 1000C
  • this cooler magma is denser, so sinks back towards the core and is reheated and begins to rise again (convection current)
  • this constant movement of magma causes the tectonic plates, which are floating on top, to be moved along
  • this movement very slow - few cm a year
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10
Q

What is ridge push?

A
  • constructive plate margin (plates moving apart)
  • magma rises as the plates move apart.
    -The magma cools to form new plate material.
  • As it cools It becomes denser and slides down away from the ridge.
  • This causes other plates to move away from each other.
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11
Q

What is slab pull?

A
  • at subduction boundary, one plate is denser and heavier than the other plate
  • the denser, heavier plate begins to subduct beneath the plate that is less dense
  • the edge of the subducting plate is much colder and heavier than the mantle, so it continues to sink, pulling the rest of the plate along with it
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12
Q

What happens at destructive/convergent plate boundaries?
continental and oceanic

A
  • denser oceanic plate subducts below the continental
  • friction in the subduction zone causes major earthquakes (area known as the BENIOFF ZONE
  • plate subducting leaves a deep ocean trench
  • rocks are scraped off the descending plate and the continental crust folds to create young fold mountains
  • oceanic crust is melted as it subducts into the asthenosphere
  • extra magma created causes pressure to build up
  • pressurised magma forces through weak areas in the continental plate
  • composite volcanoes form
  • example of ocean trench:
  • Mariana Trench
  • 10,994 metres deep
  • located east of the phillipines
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13
Q

What happens at destructive/convergent plate boundaries?
oceanic and oceanic

A
  • heavier plate subducts leaving an ocean trench
  • fold mountains will also occur
  • heavier, melting subducting oceanic plate rises through the thinner, lighter oceanic plate above it, upwelling magma and forming island arcs
  • e.g Caribbean islands
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14
Q

What happens at destructive/convergent plate boundaries?
continental and continental

A
  • subduction of oceanic crust draws continental masses together
  • as the two continental masses meet, neither will be subducted
  • instead they collide forming fold mountains
  • as neither plate can sink into denser rocks below
  • instead they are crushed, crumpled and forced upwards, usually folding in the process
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15
Q

What happens at constructive/divergent plate boundaries?
Oceanic and oceanic

A

-tectonic plates moving apart
- creates a gap between the plates where magma from the mantle rises to fill it
- as the magma cools and solidifies, it forms new oceanic crust
- sea floor spreading
- over time, the continuous spreading of the oceanic crust widens the gap between the plates and contributes to the formation of mid-ocean ridges
- mid Atlantic ridge

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16
Q

What is the evidence for sea floor spreading?

A

Paleomagnetism: study of rocks that show the magnetic fields of the Earth
- as new rock is formed and cools the magnetic grains within the rock align with the magnetic poles
- our poles switch periodically
- each time these switch the new rocks being formed at plate boundaries align in the opposite direction to the older rock
- on the ocean floor either side of constructive plate boundaries, geologists observed that there are symmetrical bands of rock with alternating bands of magnetic polarity
- evidence of sea floor spreading

17
Q

What happens at constructive/divergent plate boundaries?
continental and continental

A
  • any land in the middle of the separation is forced apart, causing a rift valley
  • volcanoes form where the magma rises, as instead of forming new oceanic crust magma rises through instead
  • eventually the gap will most likely fill with water and separate completely from the main island
  • the lifted areas of rocks are known as horsts whereas the valley itself is known as a graben
  • transform faults connect the end of one plate boundary to the end of another plate boundary
18
Q

What happens at conservative plate boundaries?

A
  • between any crust
  • parallel plates move in different directions and at different speeds
  • no plates destroyed so no landforms created
  • when these plates move, a lot of pressure is built up

e.g SAN ANDREAS FAULT:
- 10,000 earthquakes per year
- marks boundary between North American and Pacific plate

19
Q

What are hotspots?

A
  • areas of volcanic activity that are not related to plate boundaries
  • hot magma plumes from the mantle rise and burn through weaker parts of the crust
  • this can create volcanoes and islands
  • the plume stays in the same place but the plate continues to move, which sometimes causes chain of islands (such as Hawaii)
20
Q

What is the evidence for Continental drift theory?

A

MISMATCH OF CLIMATE AND SEDIMENTARY DEPOSITS:
-e.g coal derived from plants that grew/decayed in hot climates yet found in UK

FOSSIL EVIDENCE:
- similar fossils reserved in rocks of same age in different countries

GEOMETRIC FIT OF CONTINENTS:
coastline Western Africa and South America fit together

GEOLOGICAL MATCH AND CONTINUITY:
- similar rock types found on other sides of the world

21
Q

What is sea floor spreading?

A
  • process that occurs at divergent plate boundaries
  • as plates separate, magma rises from the mantle and fills the gap, creating new oceanic crust.
  • the magma cools and solidifies forming a new sea floor
  • over time, this process continues, pushing the older crust away from the plate boundary
  • this results in formation of mid-ocean ridge
22
Q

How do ocean trenches form (8)?

A
  • they are deep, elongated depressions in the ocean floor
  • they are formed through subduction
  • when two tectonic plates collide, one plate is forced beneath the other into the Earth’s mantle
  • as subducting plate sinks into the mantle, it creates a trench on the ocean floor above it
  • the downward force causes the overlying crust to bend and form a steep sided trench

A-level Physical Yr1 (14 decks)

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