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Geophysics > GEOPHYS FINAL > Flashcards

GEOPHYS FINAL Flashcards

1
Q

Alfred’s Evidence of Continental Drift

A
  1. Continents fit like a puzzle
  2. Fossil assemblages & migrations across continents
  3. Direction of past glacier movements
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2
Q

Three Types of Margins

A
  1. Constructive: Plates move apart (creates oceanic crust)
  2. Destructive: Continuous upwelling of molten material (creates volcanic arcs)
  3. Strike-Slip Faults: Two plates sliding past each other (nothing created or destroyed)
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3
Q

What are Earth’s heat sources? What do they control?

A
  1. Sun’s radiation –> controls surface water cycle, rainfall, erosion
  2. Interior heat –> controls tectonics, metamorphism, evolution of core
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4
Q

4 Modes of Heat Transfer

A
  1. Conduction: Vibrating of neighboring molecules (strongest in solids- closest together)
  2. Convection: Movement of fluid particles
  3. Radiation: Propagation of waves or photons (no medium required)
  4. Advection: Movement of heated “bulk mass” (mostly in liquids or gas
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5
Q

What modes of heat transfer are found in different portions of the Earth?

A

Solid Lithosphere: CONDUCTION
Solid Mantle: CONVECTION
Fluid Outer Core: CONVECTION
Solid Inner Core: CONDUCTION

RADIATION: Induced by hot lava and radioactive minerals.
ADVECTION: Through erosion, faulting, isostatic rebound, and tectonic movement.

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6
Q

Geotherm & Geothermal Gradient

A

Geotherm: A line or surface within or on the Earth connecting points of equal temperature.

Geothermal Gradient: The rate of change of temperature with respect to increasing depth.

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7
Q

Why was Kelvin’s calculated age of the Earth so wrong?

A

He didn’t consider temperatures at different depths– Earth is not homogeneous. In addition, convection and radioactive heat generation was unknown at the time.

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8
Q

Rayleigh-Bénard Convection

A

A buoyancy-driven flow in a container with a temperature gradient. As the fluid at the bottom heats up, its density decreases, so buoyant forces push the less-dense fluid up towards the cooler end of the container.

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9
Q

Does mantle convection also produce the geomagnetic field? Explain.

A

No. It’s not electrically conductive like the core.

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10
Q

Types of Induced Magnetization

A
  1. Diamagnetic: Weak magnetitsm in opposite direction (ie halite, quartz, calcite).
  2. Paramagnetic: Weak magnetism in the same direction as the field (ie pyrite, biotite, hematite).
  3. Ferromagnetic: Strong magnetism in the same direction (magnetite, ilmenite, pyrrhotite).
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11
Q

Curie Temperature & Curie Point Depth

A

Curie Temperature: The temperatures above which magnetic materials lose their magnetic properties.

Curie Point Depth: The depth at which rocks reach the Curie Temperature.

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12
Q

What causes geomagnetic storms (weakening field)?

A

Solar activity like sunspots and flares interacting with our magnetic field when its differential spin “unravels”.

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13
Q

What are sunspots?

A

Areas if intense magnetic field localization– formed by the tangling of magnetic field lines (differential rotation).

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14
Q

Apparent Polar Wander vs True Polar Wander

A

Apparent: The perceived movement of Earth’s paleomagnetic poles relative to a continent assuming it’s FIXED IN PLACE.

True: ACTUAL movement of the poles due to whole-Earth rotation to its spin axis. The pole shift is due to variations in movement spin inertia (mass redistribution).

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15
Q

Acceleration due to gravity is maximum where in Earth?

A

The Core-Mantle Boundary!! This is where gravitational acceleration reaches a maximum.

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16
Q

What is the Geoid & Geoid Height?

A

Geoid: The “equipotential” surface that defines the SEA LEVEL. Everywhere on the sea surface, gravitational potential is equal.

Geoid Height: The distance between the geoid and reference ellipsoid of the Earth. If there is no “gravity anomaly”, the geoid IS the reference ellipsoid!

17
Q

What can cause a geoid anomaly?

A
  • Continental collisions
  • Postglacial rebounds
  • Subduction and more plate tectonic consequences.
18
Q

How do mountains affect the geoid?

A

Excess mass, above or below the reference ellipsoid, ELEVATES the geoid, while deficient mass depresses it.

19
Q

Types of Gravity Corrections

A
  1. Latitude Correction: At any given latitude. (Subtracted)
  2. Elevation Correction: If the measurement is made above the reference geoid. (Added)
  3. Bouguer (Topography) Correction: For extra mass above the reference geoid. (Subtracted)
  4. Terrain & Tidal Corrections: For steep topography or gravitational effects from the Sun/Moon.
20
Q

Describe the Wilson Cycle

A
  1. Rift → breaking up rocks like a zipper. Once there’s a gap, oceanic crust can form.
  2. Drift (outwards) → mid ocean ridge spreads stuff outwards
  3. Initiate Subduction → the spread stuff reaches continental crust and subducts
  4. Drift (inwards) → this pushes things together
  5. Collisions & Mountain Building → makes mountains
  6. Supercontinent.
21
Q

Explain the Geodynamo Theory (Steps)

A
  1. Internal heat source from the inner core drives outer core convection
  2. Convection causes flow of molten iron; electrically conductive
  3. Earth’s rotation induces “helical” patterns of convective flow
  4. Magnetic field!
22
Q

Why is the Geodynamo Self-Sustaining?

A

A current moving along a helical path produces a magnetic field, and helical flows twist magnetic field lines to produce a current.

23
Q

1 km = ?m
1 mu m = ?m

A

1km = 1000 m
1 mu m = 1.0x10^-6 m

24
Q

What’s a Concordia diagram?

A

Describes the U-Pb parent and daughter ages in a closed system if there were no initial Pb isotopes. DISCORDIA is the real line of parent/daughter ratios, caused by a disturbance and the system to lose Pb. The intersection of conc and disc is the AGE OF FORMATION (time the disturbance occurred).

25
Q

______________________ dating is widespread. It can be used on most rocks.

A

Potassium-Argon (K-Ar)

26
Q

What is postglacial rebound/glacial isostatic adjustment?

A

The rise of land masses that were depressed by the huge weight of ice sheets. This makes the “water level decrease” (in some areas like the Hudson Bay).

27
Q

What is a half-life and what does it tell us?

A

The time required to disintegrate half of the original parent atoms.

It tells us which isotope dating is suitable for a certain age range!

28
Q

Which radioactive dating should we use when?

A

The expected age range should be about the same order as the dating half-life. For old rocks, short half-life isotopes may have already vanished!

U-Pb = 10^6 (OLD)
C-N = 1000 (YOUNG)

29
Q

Curie vs Closure Temperature

A

Curie: The temp at which rocks begin holding a magnetic signature.

Closure: The temp at which a rock isotopically stars recording an age (it has cooled enough so there is no diffusion of the parent/daughter out of the system).

30
Q

Why are meteorites good for dating the Earth?

A
  • Closed system
  • Pb to Pb isochrones
31
Q

Types of Seismic Waves

A

Body Waves:
1. P Waves
2. S Waves

Surface Waves:
3. Love Waves
4. Rayleigh Waves

32
Q

P Wave

A
  • Move along the direction of propagation
  • Fastest; travels through all media
  • Early warning
33
Q

S Wave

A
  • Move perpendicular to the direction of propagation
  • Slower than P waves; travels only through solids
  • Stronger than P waves
  • Vertical and horizontal components (SV & SH)
34
Q

Love Wave

A
  • Interaction of SH waves on the surface
  • Move along the horizontal
  • Slower than body waves but faster than rayleigh
  • Powerful and damaging
35
Q

Rayleigh

A
  • Interaction of P & SV waves on the surface
  • Move along horizontal and perpendicular (rolling motion)
  • Slower than love waves
  • Powerful and damaging
36
Q

Why are surface waves so destructive?

A

The amplitude of surface waves lasts longer over a longer distance than body waves.

Geophysics (2 decks)

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