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Earth and Ocean Systems > Development of the solid Earth and Plate Tectonics > Flashcards

Development of the solid Earth and Plate Tectonics Flashcards

Lectures 2.1-2.5

1
Q

What is the solar nebular model?

A
  • Giant swirling cloud of gas and dust (mainly H2, He, and dust created by stellar nucleosynthesis) many light years across
  • Very cold, not much rotation
  • Inherently unstable
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2
Q

What causes the nebula to collapse?

A

A shockwave that causes it to collapse under its own gravity.

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3
Q

What energy changes occur as it collapses?

A

Gravitational potential energy
into
kinetic energy
into
heat

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4
Q

How does the decreasing size effect rotation? What is this rule called?

A

As size decreases it rotates faster. Known as Conservation of Angular Momentum.

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5
Q

How does the collapse of a Nebula trigger formation of a star?

A
  • Material falls into a disk onto a protostar (very young star till increasing in mass)
  • Bipolar outflow is generated (two outflows of gas from either side of the star)
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6
Q

How does this lead to the formation of a Solar System?

A
  • The sun forms in the centre of this disk with the planets around it, orbiting in one direction
  • Leads to distinct planet formation zones with decreasing temperature
  • Rocky and gaseous planets accrete in certain areas (Gaseous accretes in ace zones around frost lines/ice zones)
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7
Q

How do rocky planets form?

A
  • Electrostatic attraction from a proto solar disk causing dust particles to slowly aggregate, forming pebbles etc etc
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8
Q

What are the two theories on the speed in which rocky planets form? Which has been supported by NASA?

A
  • Gravitational collapse (A few m/s, low velocity. Driven by gravity. Slow accumulation and then gravitational collapse forms planetesimals.)
  • High velocity capture (100s+ m/s, hierarchal accretion)
  • NASA has supported gravitational collapse model .
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9
Q

What were the 3 main steps to the formation of the Earth?

A
  • Accretion of planetesimals over 30-40 my
  • Iron rich core formation between silicate
  • Metallic cores of planetesimals break up, pool over silicates and metal descends to core.
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10
Q

What was the moon forming collision?

A
  • Planet impacts earth (about the size of mars)
  • Vaporises planet on impact, as well as some of earth
  • Moon forms from silicate vapour
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11
Q

Describe how this impact led to the creation of the first ocean.

A
  • Atmosphere was silica rock vapour, condensed and rain on earth. Magma ocean at this point due to CO2 atmosphere.
  • Cooling forms first water after moon moves away.
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12
Q

What caused the solidification of the mantle?

A

Tidal heating dissipated after the moon moves further away.

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13
Q

What is the habitable zone and has it always been in the same spot?

A

It is where water can exist on as a liquid on a surface. It has moved but the earth has always been in it.

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14
Q

What are the oldest known materials and why are none older than that?

A

Oldest material - zircon crystal. 4,4 Ga.
Oldest rock - 4.03 Ga
None earlier due to Late Heavy Bombardment 4 Ga that destroyed most of earths surface.

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15
Q

Why did the Late Heavy Bombardment happen?

A
  • Jupiter and Saturn disturbed the asteroid belt
  • During orbital resonance
  • Caused sudden instability of Solar System
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16
Q

What are the radioactive isotopes often used for dating?

A
  • U²³⁸ U²³⁵
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17
Q

Describe α radiation.

A

Two protons and two neutrons leaving the nucleus of an atom.

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18
Q

Describe β radiation.

A

A high energy electron leaving the nucleus of an atom.

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19
Q

Describe Y radiation.

A

A high energy electromagnetic photon leaving the nucleus of an atom.

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20
Q

What is a half life?

A

The time taken for half of the 14C atoms to decay.

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21
Q

What is radiometric dating?

A

The change in parent/daughter abundances through time. This depends on decay as it is an exponential process.

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22
Q

What are blocking temperatures?

A
  • Blocking: below this temperature daughters are locked into crystal and not lost over time. Above it they are lost a they can escape.
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23
Q
A
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24
Q

What are meteorites? How can we use them?

A
  • They are rocks that originated as planetesimals but were shattered due to collisions caused by Jupiter’s brutal gravitation.
  • We can use samples of them to date the earth and material on it
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25
Q

What are differentiated meteorites?

A
  • Irons and stony irons
  • 6% of earth falls
  • Fr Ni metal (with sulphide inclusions) that prove proto planet cores were already differentiated when smashed into pieces in the asteroid belt.
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26
Q

What are undifferentiated meteorites? How can we use them?

A
  • 86% of earth falls
  • Chondrites, meaning they contain chondrules (once molten spherical particles)
  • Stony silicate composition as well as elemental ratios close to sun indicate early formation from solar nebula and hence can be used to date our solar system.
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27
Q

What are the origins of chondrites?

A

Formed in protoplanetary disk of early solar system.

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28
Q

When did the earth and moon have a differentiated crust and when was this mostly destroyed?

A

Formed - 4.51 Ga
Late Heavy Bombardment - 4 Ga

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29
Q

How does pressure under the earth change with depth?

A
  • Increases with depth as weight of overlying rock increases.
30
Q

How does temperature increase with depth in the earth?

A
  • Heat is generated by radioactivity and this increases with depth.
31
Q

What is the geothermal gradient? What are the high and lows of it?

A
  • The rate at which temperature change varies with depth.
    High: 50℃ per km
    Low: 15℃ per km
32
Q

How do we use seismic waves to investigate the structure of deep earth?

A
  • The velocities of seismic waves change with density, so we can use them to determine the depth of where densities change in the earths interior.
33
Q

What are the two types of earthquake?

A

P and S waves.

34
Q

Describe P and S waves.

A

P waves: Compressional, travel through solid and liquid.
S waves: Shear, travel through solid but not liquid.

35
Q

What is the evidence for a liquid outer core of the earth?

A
  • P and S waves are refracted (bent) throughout the earth
  • S waves suddenly stop and this point is at which the core becomes solid.
36
Q

Describe the characteristics of the outer core of the earth.

A
  • 2,500km thick
  • Liquid
  • Iron, nickel, sulfur
  • Density of 10-12g/cm³
37
Q

Describe the characteristics of the inner core of the earth.

A
  • Radius of 1,200 km
  • Solid
  • Iron nickel alloy
  • Density of 13 g/cm³
  • Similar to iron meteorites
38
Q

What drives our magnetic field?

A
  • 2000km thick outer core
  • Molten iron aligns field in north south direction, generating electrical currents.
  • Acts like a big dipole bar magnet (with N at the south pole etc)
39
Q

What are the two functions of our magnetic field?

A
  • Forms a shield around Earth known as a magnetosphere that protects it from solar winds.
  • Concentrates charged particles from solar winds in Van Allen belts.
40
Q

What causes aurora borealis and australis?

A
  • When charged particles make it past Van Allen belts, they are channelled along lines of the magnetic field
  • They ionise atmospheric gases in polar regions
41
Q

Describe the characteristics of Continental Crust.

A
  • 35-40km thick on average
  • 2.7g/cm³ on average
  • Felsic
42
Q

What is the meaning of felsic?

A
  • Granitic
  • High silica composition, meaning thick
43
Q

Describe the characteristics of the Oceanic Crusts.

A
  • 7-10km thick on average, so much les dense than continental.
  • 3 g/cm³ on average, so more dense than continental.
  • Mafic
44
Q

What does mafic mean?

A
  • Basaltic
  • Gabbroic
45
Q

What is the boundary between the crust and mantle known as?

A

Mohorovičić discontinuity. Shortened to Moho.

46
Q

What is the most abundant element in the crust? Why?

A

Oxygen, due to high amounts of silicate (SiO⁴) and the fact it is a large molecule.

47
Q

Describe the lithosphere.

A
  • Outer 100-150km of earth (crust and upper mantle)
  • Rigid
  • Makes up tectonic plates and ocean ridges
48
Q

Describe the asthenosphere.

A
  • Upper mantle below lithosphere
  • Shallower under oceanic lithosphere
  • Soft solid
49
Q

What were Alfred Wegeners pieces of evidence for plate tectonics?

A
  • Fit of the continents like a puzzle
  • Distribution of fossils being found on continents fitting to each other
  • Glacial deposits far from the poles
50
Q

Are the geographic and magnetic poles parallel? Why?

A
  • No, and they are constantly varying. This difference is called declination.
  • Magnetic needle tilts due to curved field line of magnetic field. This is called inclination.
51
Q

What is paleomagnetism?

A
  • Magnetic signals archived by Fe minerals
  • If magma is hot enough there is no magnetisation and the dipole is randomly oriented.
52
Q

What is the Curie temperature?

A

The temperature in which a material loses its permanent magnetic archive. Therefore when it cools to below this temperature the magnetic dipoles are frozen into the rock.

53
Q

What is polar wondering?

A

It is the wonder of a continent on a fixed pole. It is recorded via layers of basalt under the ground.

54
Q

What were early sea floor Bathymetry experiments?

A

To ‘take soundings’ aka see how deep a lead weight went below your boat.

55
Q

What did echo sounding find and why was it developed?

A
  • Developed to detect submarines.
  • Found mid ocean mountains, deep ocean trenches near island chains, submarine volcanoes
56
Q

Describe the mechanism of sea floor spreading.

A
  1. Upwelling mantle erupts at mid ocean ridge
  2. New crust moves away from ridges, gathering sediment
  3. At trenches the sea floor subducts back into mantle.
57
Q

How did lava flows show sea floor spreading?

A
  • Stripes of positive and negative magnetic intensity in the sea floor made of lava flows. Allows us to determine rates of sea flow.
58
Q

What are the terms used for long and short term magnetic reversals?

A

Less than 200 Ka = Subchrons
500-700+ = Chrons

59
Q

What are the principles of Buoyancy and Isostacy?

A
  • Floating solid displaces water equal to their mass
  • An iceberg sinks until the mass of water it displaces is equal to the mass of the iceberg
60
Q

How is Isostatic equilibrium maintained after erosion?

A
  • Flow in the asthenosphere
  • Erosion of mountains and transport destroys equilibrium, so asthenosphere flows in to compensate and restore it.
61
Q

How is Isostatic equilibrium maintained after glaciation?

A
  • Loading my new ice sheets destroys equilibrium
  • Mantle moves out to restore equilibrium. When this moves back in as ice melts, it is called Glacial Isostatic Readjustment.
61
Q

What is a passive margin continental crust?

A
  • Crust thins toward the sea
  • Transitions into oceanic crust and traps eroded sediment
62
Q

What is a divergent plate boundary?

A

Where plates are moving apart to create new crust and mantle.

63
Q

What is the first phase of divergent plate boundary?

A
  • Lithosphere stretched as crust thins
  • Mantle upwells
  • Pressure release causes melting and volcanism develops
64
Q

What is phase 2 of divergent boundaries?

A
  • Ocean crust formation and initiation of sea floor spreading
  • Development of new continental margin
  • These create Black Smokers, metal sulphide rich plumes become unstable in the sea. They precipitate metal ores.
65
Q

What is a convergent boundary?

A
  • Where continental plate meets ocean
  • Continental is too buoyant to subduct so the oceanic one does instead.
  • Also causes continental collision when subduction ceases and creates mountains
66
Q

What is a transform boundary?

A
  • Lithosphere slides past one another, nothing is created or destroyed so no volcanism.
  • Lotta earthquakes though. None deeper than 660km but plate descent continues past this.
67
Q

What is a triple junction?

A

Where three plate boundaries meet.

68
Q

What is a hot spot?

A
  • Plumes of deep mantle material that are particularly hot
  • Burn through lithosphere add lines of volcanoes (such as Hawaii)
  • Hot spot stays in the same place but the plate moves, so a chain of islands is created.
69
Q

What are the two things that drive plate movement?

A

Ridge push: Gravity acting on young lithosphere, pushing it apart
Slab pull: Gravity pulls down a subducting plate downward

70
Q

What are two ways in which plate tectonics are essential for life?

A
  • Drives the rock cycle (recycling chemicals crucial to keeping Co2 uniform)
  • Fostered development for life (creates variety in a lot of different biome, maintaining biodiversity which is the best defence against mass extinction)

Earth and Ocean Systems (5 decks)

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