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A-Level Geology (1st Year) > Physical Structure Of The Earth > Flashcards

Physical Structure Of The Earth Flashcards

1
Q

What depth does the Crust layer reach?

A

0-35km

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2
Q

What are the properties of oceanic crust?

A

Basaltic, mafic, denser

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3
Q

What are the properties of continental crust?

A

Granitic, silicic, thicker, solid

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4
Q

What is the moho discontinuity, and where is it found?

A

35km depth
Boundary between Crust and Mantle
Solid
Silicic —> ultramafic
Distinct boundary

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5
Q

What are the properties of the upper mantle?

A

Solid, ultramafic peridotite

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6
Q

What is the depth of the upper mantle?

A

35-700km

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7
Q

What depth is the lower mantle?

A

700-2900km

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8
Q

What are the properties of the Gutenberg discontinuity, and where is it found?

A

2900km
Ultramafic peridotite —> iron & nickel
Phase boundary
Found between Mantle and Outer core

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9
Q

What is the depth of the outer core?

A

2900-5100km

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10
Q

What are the properties of the Lehmann discontinuity?

A

5100km
80% Iron, 20% nickel
Gradual phase boundary
Found between Outer core and Inner core

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11
Q

What is the depth of the inner core?

A

5100-6371km

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12
Q

What are the properties of the inner core?

A

80% Iron, 20% nickel
Solid

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13
Q

What is the deepest hole we have dug? (Depth)

A

12.2km

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14
Q

How does the existence of the magnetosphere supply evidence for the structure of the earth?

A

Helps us know there must be a liquid layer and there’s lots of iron (outer core)

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15
Q

How do we know the state of the mantle?

A

Isostacy

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16
Q

How do we know the composition of the core?

A

Meteorites share a similar composition

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17
Q

How does the study of seismic activity give us evidence of the earth’s structure?

A

P and S waves pass through the interior of the earth and are affected by state. (S can’t go through liquid)

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18
Q

How do we know the rock type of the mantle?

A

Ophiolites and Volcanic eruptions

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19
Q

What is a seismometer?

A

The equipment used to measure seismic activity

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20
Q

What is a seismogram?

A

The graph produced when measuring seismic activity

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21
Q

What is a seismograph?

A

Both the equipment and the graph produced when studying seismic activity

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22
Q

What are P waves? (Type of wave, amplitude, arrival time, travel ability)

A

‘Primary waves’
Travel through the body of the earth (body waves)
Longitudinal waves (compressional)
Travel fastest - arrive first at seismometer
Can travel through solids and liquids - faster in solids
Smallest amplitude

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23
Q

What are S waves? (Type of wave, amplitude, arrival time, travel ability)

A

‘Secondary waves’
60% speed of P waves - arrive second to seismometer
Middle amplitude
Transverse waves
Only travel through solids, no liquids
Travel through body of the earth (body waves)

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24
Q

What are L waves? (Type of wave, amplitude, arrival time, travel ability)

A

‘Love waves’
Only travel on the surface - surface waves
Most destructive
Last to arrive at seismometer
Largest amplitude
Transverse wave
Lose energy quickly
Oscillate in circular fashion

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25
Q

What are shadow zones, and why do they occur?

A

Areas where a certain seismic wave cannot be detected by seismometer.
P wave shadow zones happen due to the refraction of wave direction once it hits the liquid outer core.
S wave shadow zones happen because they cannot pass through the liquid outer core

26
Q

Why do some seismograms only show P and L waves?

A

Because they are positioned in an S wave shadow zone

27
Q

What is the velocity of p and s waves measured in?

A

Kms-¹ or km/s

28
Q

What letter is given to represent density in the equation to calculate wave velocity, and what units are used for density?

A

p
Kgm-³ or kg/m³

29
Q

Why is density relevant in calculating the velocity of waves?

A

The denser it is, the faster they travel

30
Q

What is incompressibililty measured in, and what letter is used to represent it when calculating wave velocity?

A

Pa (pascals)
The letter k

31
Q

What does Incompressibility mean when calculating wave velocity?

A

How much it can squash

32
Q

What is rigidity measured in, and what letter is used to represent it when calculating wave velocity?

A

Pa (pascals)
The letter is μ

33
Q

What is rigidity when measuring wave velocity?

A

How easily does it move

34
Q

What is the equation for calculating the velocity of a P wave?

A

√( (k+(4/3)μ) ÷ p)

35
Q

What is the equation for calculating the velocity of S waves?

A

√(μ÷p)

36
Q

What is the equation for measuring density?

A

P= m/v
Density= mass/volume

37
Q

What should you multiply by to get from 1km³ to 1cm³

A

Km³ –> m³ = x1,000,000,000
m³ –> cm³ = x1,000,000

Km³ –> cm³ = x1,000,000,000,000,000
(1 trillion)

38
Q

What is the density of the earth in gcm-³

A

5.53gcm-³

39
Q

If the density of rock at oceanic crust is 2.9gcm-³ and continental is 2.7gcm-³, what does this tell us about the density of the unmeasurable parts of the earth?

A

They must be much larger than the average (5.53gcm-³) to average it out

40
Q

What is gravity?

A

The force that attracts a body towards the centre of the earth

41
Q

What unit of measurement is used to measure gravity?

A

Gals (miligals mgals)
1gal = 1 travel at at ms-²

42
Q

How can we use a pendulum to measure gravity?

A

How quickly it travels towards the centre
It moves to the centre as it is closest to the earth’s core
Without gravity, the mass wouldn’t return to centre
The stronger the gravitational pull, the faster it travels back to the centre

43
Q

Why do gravity measurements change at different places on the earth’s surface?

A

9.81 is an average reading.
It is effected by altitude, equator distance and subduction.
Equator - the earth is slightly squashed so equator is further from core
Subduction means there are less dense zones where gravity can travel faster

44
Q

What is a gravity anomaly?

A

When measurements are more or less than the average or that we expected

45
Q

What is a positive gravity anomaly?

A

Indicates something of greater mass and/or density below the surface than we expected

46
Q

What is a negative gravity anomaly?

A

Indicates something of lower mass and/or density below the surface than we expected

47
Q

What is isostacy?

A

The rising or settling of a portion of the earth’s lithosphere that occurs when weight is removed or added in order to maintain equilibrium between buoyancy forces that push the lithosphere upward, and gravity that pull the lithosphere downwards

48
Q

What is an example of a mass that results in isostacy?

A

Glaciers/glaciation

49
Q

What does isostacy tell us about the mantle?

A

That the mantle must be plastic-y and the asthenosphere is more plastic than the rest

50
Q

What evidence do we have for the composition of the upper 250km of the earth?

A

Ophiolites, volcanoes, boreholes, mines, visible crust (look down)

51
Q

What does rigid mean?

A

Old, cold, brittle

52
Q

What does rheid mean?

A

Plastic solid, solid rock that can flow

53
Q

What is an electromagnetic survey? (A.k.a. ground conductivity survey)

A

How well the ground conducts electricity. Pass a current through the ground. Useful for detecting fluid

54
Q

What is seismic tomography?

A

Imaging technology that uses seismic waves generates by earthquakes and explosions to create computer-generated 3D images of the earth. Particularly p and s waves

55
Q

How can seismic tomography help us identify subduction zones?

A

Subducting plate is colder and more rigid than mantle
Seismic waves travel faster through colder, rigid material
In subduction zones, we get high-velocity zones

56
Q

How can seismic tomography help us identify hot spots and mantle plumes?

A

Mantle plumes produce hot spots. Shows where they are because waves slow down when travelling through rheid mantle.
Low velocity zones

57
Q

What do the earth’s magnetic fields do?

A

Earth has a magnetic field that creates a magnetosphere
Protects us from solar winds and solar radiation
Important to geologists because it contributes to evidence of earth’s core and that there is moving iron present

58
Q

Where does the earth’s magnetism come from?

A

Opposing rotation of inner and outer core. It creates a geomagnetic dynamo, sometimes called a self exciting dynamo

59
Q

What is magnetic reversal?

A

When the magnetic North and south Pole reverse. Earth’s magnetic field weakens and begins to move and eventually it flips

60
Q

How do iron rich minerals indicate paleomagnetism?

A

Igneous rocks that contain Iron rich minerals behave like frozen compasses.
When forming, when molten, iron minerals align to North, then the it solidifying. Then there’s a permanent record of the direction of north at the time of formation.
If we can date the rock, we can determine North and South over geological time.

61
Q

What is magnetic inclination?

A

An incline means “at an angle” - a.k.a rocks have dip or are dipped.
The dip of iron rich minerals in relation to how close it is to the poles
For example, no inclination (horizontal) at the equator.
The greater the dip, the closer to pole

A-Level Geology (1st Year) (11 decks)

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