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BSc Environmental Science > LEC.171 The Earth's Interior > Flashcards

LEC.171 The Earth's Interior Flashcards

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1
Q

What are the 4 eons from earliest to latest and which are part of the Precambrian period?

A

Hadean –> Archean –> Proterozoic –> Phanerozoic, Precambrian = first 3

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2
Q

What is the Earth’s core composed of?

A

Fe and Ni

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3
Q

Which planet collided into Earth to create the Moon 4.51Ga ago?

A

Theia

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4
Q

What was the Earth’s early atmosphere composed of?

A

O3, N2, and O2

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5
Q

How many Ga ago was the universe formed?

A

13-15 Ga

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6
Q

What can S waves not travel through and why not?

A

Liquids (the outer core) and gases, shear modulus is zero

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7
Q

What is seismic discontinuity?

A

A boundary between 2 layers with different seismic velocities

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8
Q

What 3 things can happen to S and P waves at seismic discontinuities?

A
  1. Reflection
  2. Refraction into a different layer (diving waves)
  3. Transformation
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9
Q

What is reflection/refraction dependant on?

A

The angle of incidence between incoming seismic wave and boundary, and the density/velocity contrast between 2 layers

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10
Q

Why does seismic velocity change between layers?

A

Differing rock density/elasticity

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11
Q

What triggered the dramatic increase in atmospheric O2 levels 580 Ma ago?

A

Continental collisions that increased rates of carbon burial by seafloor sediment

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12
Q

What is the Moho the boundary between?

A

Crust and upper mantle

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13
Q

What is S-wave velocity inversely proportional to the square root of?

A

Density

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14
Q

What is bulk modulus and shear modulus?

A

Bulk: Pressure change needed to give volume change
Shear: Pressure change needed to give SHAPE change

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15
Q

What 2 things does the water on Earth mainly originate from?

A
  1. Volcanic outgassing
  2. Comets that bombarded early Earth
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16
Q

What is the area on the Earth’s surface 105-142° away from an earthquake where no DIRECT P-waves are recorded called?

A

The shadow zone

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17
Q

What do shadow zones show the presence of at 2900 km?

A

Core-Mantle Boundary

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18
Q

What is the mantle and asthenosphere made of?

A

Mantle: Peridotite
Asthenosphere: Peridotite and melt (lower elasticity so lower seismic velocity)

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19
Q

What are the meanings of P, S, K, I, J, c, and i in terms of P and S-wave movement e.g. PKIKP?

A

P: P-wave in mantle
S: S-wave in mantle
K: P-wave in outer core
I: P-wave in inner core
J: S-wave in inner core (solid)
c: Reflection off outer core
i: Reflection off inner core

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20
Q

What was discovered using identification of the PKIKP phase and why?

A

Inner core, S-waves reappear so inner core must be SOLID

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21
Q

What type of movement do P and S-waves have and which wave type is faster?

A

P: Push-pull
S: Side-to-side
P-waves are faster

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22
Q

What type of rock do seismic waves travel faster through?

A

Igneous

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23
Q

What type of boundary is the Lithosphere-Asthenosphere Boundary?

A

Thermal boundary layer (mantle becomes partly molten)

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24
Q

What do mantle transition zones reflect with examples?

A

Changing mineral structure as pressure increases
Olivine –> spinel –> perovskite (increase in density/elasticity/seismic velocity)

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25
Q

What are 3 ways we know the mantle’s composition?

A
  1. Ophiolite suites
  2. Xenoliths
  3. Meteorites (similiar appearance)
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26
Q

How do ophiolite suites allow us to know the mantle’s composition?

A

Mantle peridotite brought to the surface by tectonics = peridotite mantle

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27
Q

How do xenoliths allow us to know the mantle’s composition?

A

Mantle peridotite fragments carried to the surface in magma

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28
Q

What does the Earth’s magnetic field require the convection of and how is this affected?

A

Electrically conducting liquid in the outer core (self-exciting dynamo), fluid flow affected by solid inner core and rotation

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29
Q

What are magnetic field reversals caused by and when do they happen?

A

Caused by change in core convection pattern, happen at random time periods

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30
Q

Where is the Earth’s magnetic field currently weakening?

A

Bolivia

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31
Q

What are 5 oceanographic research methods?

A
  1. Echo sounding
  2. Seismic reflection profiling
  3. Dredging
  4. Drilling
  5. Submersibles
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32
Q

What features of ocean basins have been discovered using echo sounding and seismics?

A

Contain abyssal plains, trenches with max depth of 11km and networks of mid-ocean ridges (MORs)

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33
Q

What features of ocean basins have been discovered using dredging, drilling, and submersibles?

A

Seafloor is mostly sediment-covered with volcanic rocks beneath and recent volcanic activity at MORs

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34
Q

What do active and passive continental margins have?

A

Active: Steep continental shelf + ocean trenches (more EQs/tsunamis)
Passive: Sloped continental shelf

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35
Q

What are MORs offset by and what does this form?

A

Fracture zones, perpendicular steep scarps

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36
Q

What are transform faults?

A

Plate boundaries/fracture zones between offset ridges

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37
Q

What are the 3 main sources of deep sea sediment?

A
  1. Terrigenous sediment - transported from land to ocean by rivers
  2. Pelagic clays - fine particles that settle in deep, calm water
  3. Pelagic oozes - remains of microscopic organisms (calcareous/radiolarian)
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38
Q

What do calcareous and radiolarian mean?

A

Calcareous: CaCO3
Radiolarian: SiO2

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39
Q

What are basaltic pillow lavas?

A

Blobs of lava that rapidly cool on contact with seawater

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40
Q

What are sheeted dikes?

A

Vertical blades of cooled magma

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41
Q

What is gabbro?

A

Cooled, coarse-grained igneous rock with the same chemical composition as basalt (layered at bottom due to crystal settling)

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42
Q

Where do 95% of earthquakes happen and what types of faulting are present?

A

Ocean trenches, extensional (normal) and compressional (thrust) faulting

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43
Q

What do Wadati-Benioff zones show?

A

Lithosphere remains solid as subducted until below 700km where it is heated, softened, and flows instead of fracturing

44
Q

Why is it difficult to date seafloor basalt samples using radioactive isotopes and what technique is used instead?

A

Radioactive isotopes altered by seawater, drilling to retrieve sediment cores (sediment age/thickness increases away from MORs)

45
Q

Which magnetic mineral is present in basalts and gabbros?

A

Magnetite (Fe3O4)

46
Q

How is the magnetism of oceanic crust determined?

A

Lavas on land dated to establish global magnetic stratigraphy and applied to oceans

47
Q

What are chrons and subchrons?

A

Chrons: Long periods of mostly normal/reversed magnetism
Subchrons: Shorter reversals within chrons

48
Q

How can any ocean floor be dateable?

A

Counting stripes from ocean magnetic anomalies parallel to MORs

49
Q

What are 4 pieces of evidence of continental drift?

A
  1. Jigsaw fit of continental coastlines
  2. Similar geological histories
  3. Plant/animal fossil distribution
  4. Polar wander (looking at ancient lavas, magnetic poles appear to have wandered over time)
50
Q

What is an example of an oceanic divergent plate boundary?

A

Mid-Atlantic Ridge

51
Q

What is an example of a continental divergent plate boundary (thinning lithosphere, chains of volcanoes)?

A

East African Rift Zone

52
Q

What is an example of an oceanic convergent plate boundary (island arcs)?

A

Lesser Antilles

53
Q

What is an island arc?

A

Chain of volcanic islands parallel to an oceanic trench at an oceanic convergent plate boundary

54
Q

What feature do continental convergent plate boundaries have?

A

Continental collision zones - continental lithosphere too thick/buoyant to subduct)

55
Q

What feature do oceanic conservative plate boundaries have?

A

Transform faults (can offset ridges, trenches, or both)

56
Q

What feature do continental conservative plate boundaries have with an example?

A

Transform fault systems (complex band of almost parallel faults), San Andreas Fault

57
Q

What is a triple junction?

A

Point on Earth where 3 plates meet

58
Q

What are displacements on a sphere surface equal to?

A

Rotations about the Euler pole/pole of rotation (each plate has a different Euler pole

59
Q

What indicates relative plate motion?

A

Orientation of transform faults between plates

60
Q

What is the relative speed of plates to a neighbouring plate or MOR revealed by?

A

Magnetic anomalies/stripes on seafloor (but MORs/other plate boundaries aren’t stationary)

61
Q

Why does relative plate speed vary along the length of the plate boundary?

A

Greater distance from Euler pole

62
Q

What type of quantity is plate motion?

A

Vector

63
Q

How are absolute plate velocities measured?

A

Using radiometric dating of lavas from different Hawaiian islands plotted against distance (plate motions carry extinct volcanoes away from stationary hotspots)

64
Q

What are present-day plate motions measured with?

A

GPS - satellites emit radio signal with precise atomic clock and precise position independent of plates, repeated to detect movement over the years

65
Q

What caused the Early Earth lithosphere to form?

A

Cooling of the magma ocean

66
Q

What are 2 sources of heat in the Earth?

A
  1. Kinetic energy in Earth’s accretion
  2. Radioactive decay
67
Q

How is the Earth’s interior slowly cooling?

A

Via heat flow from interior to surface (varies across Earth’s surface)

68
Q

Where is there the most heat flow?

A

At O-O divergent plate boundaries

69
Q

Which heat flow mechanism is the main mechanism on Earth?

A

Convection

70
Q

Why is there less heat flow at the continental crust and what fraction of continental heat flow is produced in situ?

A

Thicker, more complex structure/composition, much older, 2/3

71
Q

Where is there more continental heat flow?

A

Where there has been recent rifting/volcanism

72
Q

What % of the planet’s total surface heat flow is hydrothermal circulation responsible for?

A

25%

73
Q

What is mantle convection driven by?

A

Density contrast (hotter material = less dense/more buoyant)

74
Q

Where is seismic velocity faster at (seismic tomography)?

A

Cool, thick continents

75
Q

What are 2 features of fast-moving plates?

A

Little continental area, long subduction zones at margin

76
Q

From slab pull and continental drag, which is the main driving force and which is the main retarding force?

A

Driving force: slab pull
Retarding force: continental drag

77
Q

What do subducting plates provide?

A

Main driving force for plate tectonics

78
Q

What is isostasy?

A

Lithosphere sticks down into asthenosphere much more than it sticks up above sea level

79
Q

What is a Wilson cycle?

A

Continents grouping into supercontinents, then rifting apart via the opening and closing of oceans

80
Q

What is the evidence for Wilson cycles?

A

Present day North Atlantic margin lies in close proximity to much older faunal divide

81
Q

What are the 8 steps to a Wilson cycle?

A
  1. Rift basin
  2. Young passive margins
  3. Mature passive margins
  4. Oceanic subduction
  5. Mature subduction/early collision
  6. Continental orogen
  7. Stable continent
  8. Cratonic sag basins
82
Q

How did continental crust form?

A

Early Earth magma pooled in mafic crust which increased silica content, making crust less dense –> crustal emersion

83
Q

Which 2 of the past supercontinents can be reconstructed and what was there an increase of for each supercontinent?

A

Pangea and Rodinia, zircon crystals

84
Q

How could supercontinents be considered self-destructive?

A

Continental collisions = unusually thick crust –> insulates mantle so heat builds up –> drives expansion –> uplift/rifting –> MOR

85
Q

What minerals is peridotite in the mantle made up of?

A

Olivine, pyroxenes, and plagioclase/spinel/garnet

86
Q

Which mineral has the higher melting point out of olivine and pyroxene, what is the gap between their melting points called, and what is melting temp. dependant on?

A

Olivine, melting range, pressure, composition and temp.

87
Q

What do solidus and liquidus mean and where does melting first take place?

A

Solidus: Entire mantle is solid
Liquidus: Entire mantle is liquid
Mineral boundary

88
Q

What does the partial melting of peridotite produce?

A

Basaltic magma

89
Q

What type of melting takes place at MORs and continental rift zones and how does this happen?

A

Decompression melting, plates diverge so mantle rises to fill gap so pressure decreases and melting point reached

90
Q

What type of melting takes place at hotspots and how does this happen?

A

Decompression, hot mantle plume rises so pressure decreases and melting point reached

91
Q

What type of melting takes place at subduction zones and how does this happen?

A

Fluid-induced, hydrothermal circulation at MORs chemically alters crust so rich in hydrated minerals –> H2O released, rises and percolates through lithosphere –> peridotite in NON-SUBDUCTING lithosphere melts

92
Q

Explain fractional crystallisation

A

Basaltic magma cools so dense mafic minerals (olivine/pyroxene) crystallise + settle so remaining melt more silica-rich and less dense

93
Q

What is the order of types of rock from least to most silica content?

A

Basalt –> andesite –> dacite –> rhyolite

94
Q

Are silicic or basaltic LIPs (Large Igneous Provinces) more common?

A

Basaltic

95
Q

Where are most flood basalts found?

A

Distant/extinct end of hotspot chain (aseismic ridges)

96
Q

What 2 features do the origins of magma plumes have?

A
  1. Very hot
  2. Much slower S-waves
97
Q

What is the plume model?

A

Buoyant rise of anonymously hot material through mantle –> head approaches surface + decompression melting produces high volumes of magma –> flood basalt eruptions

98
Q

What carries the LIP away from the tail of the magma plume?

A

Plate movements

99
Q

What is an example of a volcanic aerosol and does it cool the Earth?

A

H2SO4, scatter incoming solar radiation

100
Q

Which gases released from volcanic eruptions react with H2O to form acid rain?

A

CO2, HCl, SO2

101
Q

Which layer of the atmosphere has far higher wind velocities?

A

Stratosphere

102
Q

What do the atmospheric impacts of a volcanic eruption depend on?

A
  1. Explosivity (injection height)
  2. Magma SO2/CO2 content
  3. Eruption duration/latitude (equatorial = global impact)
103
Q

How do Wilson cycles affect climate?

A

Moist air rises over mountains formed from continental collisions so high ppt. –> enhanced chemical weathering removes atmospheric CO2 –> global cooling

104
Q

34 Ma ago, what did the abrupt climatic cooling coincide with?

A

India-Eurasia collision

105
Q

What % of marine species disappeared during the Permian-Triassic extinction, what was it caused by, and what could have been a trigger?

A

90%, acid rain/global warming/ocean anoxia, Siberian Traps LIP erupted around this time (increased CO2)

BSc Environmental Science (13 decks)

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