Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Earth Sciences > Lectures 21-24 > Flashcards

Lectures 21-24 Flashcards

1
Q

On average, how old are continents?

A

2.4 Billion years old

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Basic features of Asia

A
  1. Shallow earthquakes (<30km)
    - virtually no deep ones so no longer subducting (India under Asia)
    - slowed and eventually stopped
  2. Earthquakes mainly at reverse (aka at low angles = thrust) and strike-slip faults
  3. The Mountains are a U shape as the rock ‘flows’ out
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is India in the position it is?

A

Fragment of Gondwanaland
- broke away from Africa and Antarctica at 150-125 Ma

  • Collision with Asia through Mesozoic
  • roughly 150mm yr-1
  • convergence slowed to 50mm at 40Ma
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Distribution of faults in Asia

A
  1. Thrust faults bound the high mountains (Tibet and Himalaya)
  2. Strike-slip important throughout
  3. Conjugate pattern
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two main thrust faults and which is active?

A

Main central thrust
- inactive

Main Boundary Fault
- active

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is most of the energy in stars released?

A

by fusion of
H1 and H2 into helium and a high energy photon

  • EXOTHERMIC
  • then helium added to get more elements
  • why more abundant at even atomic numbers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What element can fusion go upto

A

Iron 56
- most stable nuclide

  • higher then the reactions is endothermic so no fusion - instead = neutron capture
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Beta decay

A
  • neutron into proton and electron - electron ejected

- same atomic mass but increases atomic number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Neutron capture 2 processes

A
  1. s-process (slow)
    - some fusion reactions produce flux of neutrons
    - neutron flux from this relatively low
    - lots of time to undergo beta decay after capture
    - highest = Bi 209
  2. r-process (rapid)
    - some situations have very high flux of neutrons
    - so add neutrons a lot on after the other
    - some nuclides only made by this process
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How did the solar system form?

A

nebula containing hydrogen and helium
- exploded

  1. Gravitational contraction of rotating gas cloud leads to dense central region and more diffuse flattened region
  2. Dust particles into a disc
  3. numerous planetesimals - collisions
  4. Eventually larger capture smaller
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When did the Earth’s atmosphere form?

A

129 I r-process into 129Xe by β decay

  • 17Myr half life
  • atmosphere contains less 129 Xe, relative to other Xe isotopes, than the mantle
  • Some iodine stayed behind in the mantle and the atmosphere had to form while 129 I was still active
  • very early development
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Isotope geochemistry that can estimate universe age

A

Re and Os
- in iron meteorites
- 187 Os in s-process but some from decay of 187Re only in R
- Re very long half-life = 4 x 10^10 years
Due to this ratio and also the Re decay indicate 8.65 Ga age minimum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When did the Earth’s core form?

A

182 Hf formed by r procoess and decays into 182W
- half life of 9Myr

  • Hafnium fits preferentially into silicates minerals = mantle and crust
  • Tungsten for Iron and Nickel and so core
  • look for 182W in relation to other tungsten isotopes
  • Mantle higher W than carbonaceous chondrites

iron meteorites have smaller than cc as well

OBSERVATIONS INDICATE

  • core of planetesimals and mantle formed within parent bodies while 182Hf still active
  • so within 3 Myrs of solar system start
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Continent formation

A

147Sm into 143Nd

  • 1.06 x 10^11 half life by α decay
  • continental crust separated from mantle by some melting process
  • during melting Nd prefer liquid and Sm for solid
  • so 143 to 144Nd
  • Model age - assumes single melt event
  • 1.8-2 Ga
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How much sediment is subducted back into mantle?

A

86Sr much greater in continents and continent-derived sediment than in mantle

  • so this signature like a dye for continent sediment
  • show very little sediment returned to mantle - usually incorporated back into mountain belts
  • CONTINENTS VIRTUALLY INDESTRUCTIBLE
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Africa- where is continent separating

A

rift valleys of East Africa

  • 3-4mm per year
  • many sub-parallel fault scarps - bound basins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a graben?

A

A basin formed by separating continent

  • rarely symmetrical (usually faults in one direction) and the asymmetrical ones are half-graben
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Faults around Greece

A

Arc of earthquakes following southern and western border of Greece and Aegean
- subduction zone where med floor under crete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Evolution of a normal fault

A

GRAPH

20
Q

What limits the height of mountains?

A
  • isostatic equilibrium is not stress balance
  • after height reached then not supported by isostasy
  • spread out from mountain
  • flat plateaux made
21
Q

Why are continents different?

A
  1. continental crust is more silica-rich than mantle
  2. so less dense than mantle - this inhibits its subduction
  3. Also weaker than oceanic crust and mantle - more susceptible to deformation by creep
  4. Continents can be very old - unlike oceanic
  5. So continents have many old faults - these can be reactivated
22
Q

Energy sources on the Earth

A
  1. Plate motions = earthquakes, mountain building, deformation, volcanism, metamorphism
    - account for about 2 x 10^11 W
  2. Heat loss about 4 x 10^13 W
    - most lost through spreading ridges
    - Others are radioactive decay
    - residual heat from formation of earth
  3. Sun
    - 1.73 x 10^17
  4. Humans
    - 1.2 x 10^13
23
Q

Conduction in the Earth

A
  1. rocks poor conductors
  2. thermal time contant = l^2/π^2k

k= thermal diffusivity = thermal conductivity/density x specific heat capacity

24
Q

Rayleigh number

A

Ra = ratio to show if system transfers heat by convection or conduction

=(ρgαΔT(l^3))/κμ)

25
Q

Diagrams for temperature versus depth distribution

- in earth

A

GRAPHS

26
Q

Pattern of mantle convection

A
  • hard to observe - cant see through plates
  • correlate gravity and topography
  • where surface raised due to uplift from rising - mantle plume
  • reduce gravity as hot is less dense
  • diagram
27
Q

Scales of convection

A
  1. large-scale convection
    - plates move from ridges to trenches
  2. small-scale convection pattern
    - indicated by age-depth relationship in the oceans
    - flattening of root t

BOTH = partially decoupled by low velocity zone - most likely also the low viscosity zone
- so probably no close correlation between the two

28
Q

Do we know how deep the convection currents go into the asthenosphere?

A

no- some believe entire mantle

  • others think upper mantle - shallower than 650km
  • essentially independent from that in the lower mantle
29
Q

What are hot spots?

A

Sites of volcanism

  • above rising convecting plumes in asthenosphere
  • known to move relative to each other but slowly compared to the relative motion between plates
  • provide an ‘absolute’ reference frame to look at motion of plates relative to the asthenosphere
30
Q

Little correlation between plate area and absolute velocity

- what does this suggest?

A

Shear forces on the base of the plates are not important

31
Q

What is slab pull

A
  • indicated to be significant by the length of the subduction zones on the plate boundary which correlate with plate velocity
  • arises from the density differences between the cold dense plate and relatively hot, light surrounding lithosphere
  • phase change of basalt rocks of the ocean floor to dense eclogite - significant additional force
  • oceanic part of plates are the cold dense, strong conductive boundary layers of convecting system.
  • They fall back into the asthenosphere under their own weight
  • back in asthenosphere slowly warm up and incorporated into general asthenosphere circulation
32
Q

Surface of the moon

A
  • rugged and cratered highland regions = mainly igneous rocks 4-4.6Ga - plagioclase feldspar
  • darker parts are smoother mare/seas made of younger basalts - 3.8Ga

CRATERS

  • meteorite impact structures
  • suggest heavy bombardment from formation to 3.8Ga
33
Q

When did most of the tectonic and volcanic activity stop on the moon

A
  1. 5-3Ga

- very different earth which is still active

34
Q

Contrast moon to earth

A

1/100th mass of Earth

cooled more quickly due to SA:V

35
Q

How was the Moon formed

A

Dont know
- could be 2 different

  1. Condensation of silicate atmosphere from impact to Earth
  2. CHECK
36
Q

Composition/surface of Mars

A

radius roughly half of earth

  • g only a third of Earths
  • this could be because
    1. onset melting by adiabatic decompression of mantles
    2. Lithosphere maybe twice as thick as on earth

-60 degrees
water in ice on polar caps (or in near surface rocks)

  • surface - looks like a network of drainage channels - maybe from rivers
37
Q

Rock magnetism on mars

A

Southern - stripes but in a different pattern from the one seen from Earth plate tectonics

38
Q

Mars Atmosphere

A

thin

  • gravity also weak
  • so bits knocked off by meteorites
  • These then to Earth as Martian Meteorites
  • from bubbles
  • isotopic composition must be from fractionation of the isotopes
  • this needs:
    1. Mean free path of nitrogen molecules in upper atmosphere
    2. Velocity - depends on temperature
39
Q

Marian Meteorites

A

1300Ma

- basaltic breccias with glass that traps bubbles of atmosphere

40
Q

Composition of Venus

A
  • same size as Earth
  • surface temp of 450 degrees as closer to sun by 40 million kilometres
  • Atmosphere of CO2 and sulphuric acid
  • surface pressure 90x that of Earth
  • NO WATER ON SURFACE
41
Q

Surface of Venus

A

Impact craters

  • only the bigger meteorites survive through dense atmosphere
  • use to estimate age of surface
  • 500 million years
  • lots of evidence for faulting and volcanic
  • maybe some plate boundaries
  • dont know
  • also then how does it renew surface?
42
Q

Is there mantle convection on venus

A

Evidence for it

- residual topography shows that some areas must be held up by mantle convection

43
Q

Io

A
  • density and size between the Moon and Mars
  • Orbital resonance with Europa keeps interior hot enough to cause melting
  • Voyager 2 observed eruption plumes
  • probably both silicate and sulfur

Lack of craters suggest surface is active

44
Q

Europa

A

cracked surface- mostly ice, with few craters suggests tectonic activity

  • density half of moon
  • some liquid maybe from tidal heating
45
Q

Enceladus

A

Saturn

  • small and icy
  • old cratered terrain overlain by smoother areas (no impact craters so young)
  • very reflective
  • icy eruptions which indicates
  • oceans of liquid water under ice crust
46
Q

Triton

A

Largest satellite of Neptune

  • bright solar cap of frozen nitrogen from plumes
  • mostly water-ice with frozen methane and maybe ammonia
  • Smooth areas are probably icy lavas

Earth Sciences (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions