Brainscape's Knowledge GenomeTM

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


See full index

1A Earth > Introduction to the Earth (Lectures 1-4) > Flashcards

Introduction to the Earth (Lectures 1-4) Flashcards

1
Q

What are the differences between P-waves and S-waves released in an earthquake?

A

P-waves are faster

P-waves longitudinal, S-waves transverse

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

What are the P and S wave velocity equations?

A 
Vₚ = sqrt((κ + 4μ/3)/ρ)
Vₛ = sqrt(μ/ρ)
κ is compressibility
μ is shear modulus
ρ is density
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why do S-waves not travel through liquids?

A

μ = 0 in a liquid

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

What are excited by big earthquakes?

What are they useful for?

A

Normal modes of the Earth

Interior density and velocity structure of the Earth

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

What are the shadow zones for P and S waves?

A

Direct P and S shadow zone from 103° to 142°

Direct S shadow zone 142° to 180°

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

What do the shadow zones for P and S waves reveal?

A

The outer core is liquid

The inner core is solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which law do P and S waves obey?

A

Snell’s Law

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How was the Moho found?

A

Beyond 250 km the first P wave arrival was earlier than if it travelled purely in the crust
Must be a jump from 6 km/s to 8 km/s at crust/mantle boundary

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

What did the jump in velocity at the Moho indicate?

A

A change in composition or mineral structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the Low Velocity Zone (LVZ)?

A

A drop in velocity for S and P waves at 100-150 km depth from partial melting of mostly solid mantle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why are carbonaceous chondrites significant when discussing the Earth?

A

Close in composition to the original nebula the solar system was formed from
Richer in iron than rocks in the mantle and crust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What evidence is there that the chondritic model of the Earth is applicable?

A

Comparing abundances of elements in carbonaceous chondrites and the Sun matches up with most elements bar volatile ones

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

What does the chondritic model imply?

How is this consistent with seismological data?

A

The mantle is mostly silicates
The core is >90% iron and some nickel
The core-mantle boundary at 2800km gives correct bulk composition and average density for Earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where does the Earth’s magnetic field originate from?

A

Interior is too hot (4000°C at the core-mantle boundary) for a permanent magnet
Sustained by a self-exciting dynamo: core conducts electricity (made of iron), motions maintained by a heat source (crystallisation of the inner core) driving convection currents (outer core as viscous as water)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Outline the Geological Cycle

A

Sedimentation -> burial deep in crust -> folding, faulting, mountain-building and igneous intrusion -> erosion and flattening of mountains ->

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is an effect that arises from the Geological cycle?

A

An unconformity

Bottom layers are vertical, top layers are horizontal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are facies?

A

An environment of deposition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are ooids?

A

Sand size, white ellipsoids of concentric layers of the mineral calcite deposited on a nucleus

19
Q

How do ooids form?

A

Shallow turbulent water (waves) by precipitation

20
Q

What are glacial sediments comprised of?

A

Boulder clay and gravels

21
Q

What are the two climate states the Earth has gone between over the last 2 Ma?

A

Interglacials: a little ice, like today
Glacials: lots of ice, lower sea levels

22
Q

What are foraminifera? What are they used for?

A

Small marine micro-organisms, typically <1 mm

Paleoenvironment indicators: in glacial periods sea water is very enriched in Oxygen-18 and ice enriched in Oxygen-16

23
Q

What orbital effects are there for global temperature?

A

Eccentricity
Tilt
Precession

24
Q

What features are there that suggest an ice age?

A 
Glacial striations
Varves
Drop-stones
Boulder clays
Tills
25
Q

Rocks behaving elastically means what?

A

The deformation is recovered if the forces are removed

26
Q

What do brittle substances do?

A

Fracture without appreciable permanent deformation away from the cracked surface
Like slip on faults

27
Q

What do ductile substances do?

A

Deform appreciably by flow

28
Q

What is cataclastic flow?

A

Repeated fractures which progressively reduce the grain size and allow the fragments to slide over each other

29
Q

Where is cataclastic flow common?

A

Fault zones

30
Q

Crystalline solids flow by what?

A

Creep

31
Q

What is creep?

A

Very slow flow under a constant load

32
Q

What are the three ways creep can happen at the crystal level?

A

Movement of dislocations, which are imperfections in the atomic arrangement within crystals
Sliding of crystals on grain boundaries
Recrystallisation

33
Q

What are creep mechanisms sensitive to and how?

A

Temperature

Rocks creep more easily when hotter

34
Q

What is homologous temperature?

A

Ratio of actual temperature to melting temperature

T/Tm

35
Q

When does creep appear?

A

Homologous temperature above 0.6

36
Q

What is power law creep?

When does it occur?

A

Motion on polygonal cellular patterns of dislocations within grains, with grain boundary sliding and some recrystallisation
Happens above homologous temperature of 0.55

37
Q

What is diffusion creep?

When does it occur?

A

Migration of atoms within crystals or along grain boundaries

Homologous temperature above 0.85

38
Q

When is power-law creep dominant?

A

Relatively low homologous temperature and relatively high stress

39
Q

When is diffusion creep dominant?

A

Relatively high homologous temperature and relatively low stress

40
Q

What is the asthenosphere?

A

Homologous temperature is about 0.85 at these depths

Most creep by diffusion

41
Q

What is the lithosphere? (5 points)

A 
Top 100-125 km of the Earth
Relative strong and cold
Rigid spherical caps of plates
Top part is brittle
Lower part is warm and has dislocation creep
42
Q

What is the mantle made of?

A

Peridotite

43
Q

Why are crust and mantle not the same as lithosphere and asthenosphere?

A

Crust and mantle refer to compositional structure
Sharp boundary
Lithosphere and asthenosphere refer to mechanical layering
Gradational boundary

44
Q

What is viscosity?

A

The ratio of shear stress to strain rate

How well something flows (low = runny)

1A Earth (15 decks)

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