dynamic earth Flashcards
(220 cards)
1
Q
earths spherical shape shows…
A
Earths spherical shape means that earth is dominated by gravity due to gravity pulling everything together. It also shows that earth has a low strength as gravity can pull the plant into a sphere.
- You could say the asteroid has greater strength as it has an irregular shape.( the asteroid Ida has an irregular shape)
2
Q
what is the effect of the moon on earth?
A
it helps to stabalise the planet and effects the climate cycle
3
Q
what do moving clouds give evidence for?
A
evidence of atmosphere
4
Q
over large distances and long times, the earth behaves like..
A
a fluid with no strength
5
Q
around what is the earths average radius?
A
6400km
-Equatorial radius 6,378,137 m
– Polar radius 6,356,752 m
– mean radius ~ 6,371,000 m
~ 6400km
6
Q
- Though Everest is the highest peak (8,848m) and challenger deep is the deepest (10,898m) they are not the furthest away/ closest to the centre of the earth. why?
A
due to the earth not being completely sherical.
These records go to the summit of Kilimanjaro and the Aleutian trench.
7
Q
why is challenger deep so deep?
A
it does not fill up with sediment like holes that are close to continents
8
Q
what is the average height of land?
A
0-1 km
9
Q
what is the average depth of the sea?
A
4-5km
10
Q
the coastline does not represent …
A
the boundary between ocean and continent
the boundary between continent and ocean are normaly below water.
11
Q
what does this image show?
A
The hypsometric curve shows % of earth at certain heights.
+ From this curve you can see most of earth is just above or well below sea level. There is a large jump between the two heights.
+ The boundary at 2km depth is around about the boundary between continent and ocean.
12
Q
how can satellites tell the bathymetry of the sea?
A
A bulge in the sea floor will mean more mass, thus more gravity. This extra gravity means that the bulge can pull water towards it more than the flatter areas around it. This causes the overall sea level around it to also bulge. A satellite can then send microwaves to the sea level and then workout the distance. By doing this for several areas you can see changes in the sea level and thus workout the shape of the sea bed.
13
Q
describe and name the areas at a passive margin boundary between continent - ocean transition.
A
14
Q
The earth’s continents stick up out of the ocean because…
A
The earth’s continents stick up out of the ocean because the continental crust is made of thick, low density rock that floats high in the mantle
15
Q
The earth’s ocean basins lie deep below the ocean surface because
A
The earth’s ocean basins lie deep below the ocean surface because the oceanic crust is made of thin, high density rock that floats low in the mantle.
16
Q
state ocean
composition
Thickness
Age
height
structure
A
composition ~ basaltic
Thickness ~ 7 km
(7km gets you about 4-5 km below sea level)
Age < 200 My
depth ~ -5000 m
structure- simple
17
Q
state continent
composition
Thickness
Age
Surface
structure
A
composition ~granitic
Thickness ~ 35 km
(35 km gets you a few 100m above sea level)
Age up to 3.5Gy
Surface~+500m
structure - complicated
18
Q
what are the compositon of nitrigon, oxygen, argon and carbon dioxide in the atmosphere?
A
nitrogen - 71%
oxygen - 21%
argon - 1%
carbon dioxide - 0.035%
19
Q
there are few crators on earth, what does this show?
A
Because there are few craters on earth it shows us that the crust is active and young as the craters are quickly removed. Through:
- Erosion
- Deposition
- Volcanism
- tectonics
Otherwise we would look like other planets with many craters (moon, mars and Venus)
The atmosphere, ocean, surface and interior are all active.
Evidence for active processes include lava and ash covering the land, ice sheets carving out valleys in the land.
Ice sheets are also changing size and shape often as environment changes
20
Q
what do you normally find at tectonic plate boundaries?
A
volcanoes
earthquakes also follow the same pattern
21
Q
what type of fault is this?
A
normal fault
22
Q
what type of fault is this?
A
thrust fault
23
Q
what type of fault is this?
A
strike - slip fault
24
Q
what is the lithosphere, what does the lithosphere include and how deep is it?
A
the lithosphere is the material that the plate is made of.
the llithosphere runs from the top of the crust to a little bit down into the mantle.
it is about 100km thick
crust and lithosphere are not the same thing.
25
plates are made up of...
plates are made up of both the crust and the lithosphere
26
plates move laterally over a weaker interior, and carry the continents around.
there is little friction between ____________ and the \_\_\_\_\_\_\_\_\_, thus can move laterally without disruption.
• Plates move laterally over a weaker interior (the asthenosphere), and can carry the continents around
There is little friction between the lithosphere and the asthenosphere, thus can move laterally with disruption.
27
on average what is the plate movement each year?
plates move about **1-20cm per year**
28
how are there thin and fat regions of earthquakes on this map?
In subduction zones the oceanic plate that heads downwards causes earthquakes. The smaller the angle the fatter the region.
At divergent margins there are only the two plates moving away from each other so is a thin margin
29
new lithosphere and new oceanic crust is formed at...
new lithosphere and new oceanic crust is formed at divergent boundaries at mid-ocean ridges.
30
describe the bathymetry at a mid-ocean ridge.
Dotted line is not a fault.
Both sides are moving together.
They are scars from when transform fault was there.
31
old oceanic lithosphere and old ocean crust is destroyed and recycled at.... and is marked by....
• Old oceanic lithosphere and old ocean crust is destroyed and recycled at **convergent boundaries at subduction zones** marked by **ocean trenches, island arcs, and active continental margins.**
32
trenches at subduction zones are normally not very deep. why?
the trenches normally fill up with sediment so its about 1km deep
33
\_\_\_\_\_\_\_\_\_ and __________ faults preserve lithosphere.
\_\_\_\_\_\_\_\_\_ are normally in the ocean and link \_\_\_\_\_\_\_\_
if it doesnt do this then its called a ________ \_\_\_\_\_\_\_ fault.
Transform and strike-slip faults preserve lithosphere
Transform faults are normally in the ocean and link two ridges.
If it doesn’t do this then it’s called a strike-slip fault.
34
name three things that cause melt, put them in order of importance, and give an example of where you would find them.
Hot - least important (hot spots)
Low pressure - most important (mid-ocean ridge)
Wet - second most important (island arcs, subduction zones)
35
around where is the boundary between lithosphere and asthenosphere?
what heat transport dominates the two depths?
and give a brief description of the overall rock type. in terms of temperature, rigidness, and ductileness.
at around 100km, however the boundary change is not well defined.
in the **lithospere it is thermal conduction.**
(heat is transferred through thermal conduction into the sea water and then ultimately into space
in the **asthenosphere it is thermal convection**.
(it is close to melting point but is still a solid)
in the **lithosphere** it is:
colder
more rigid
less ductile
in the **asthenosphere** it is:
hotter
less rigid
more ductile
36
as pressure increases, melting point \_\_\_\_\_\_\_
describe a temperature vs pressure graph including the solidus and liquidus( give an explanation of both).
as pressure increases, melting point increases.
**solidus** is where it just melts
**liquidus** is when its about to freeze
37
what is produced when a geotherm and solidus line crosses on a temperature vs depth graph
To produce melt, the geotherm and solidus must cross.
38
explain the effect of increasing the temperature on a geotherm and thus the amount of melt produced
increasing temperature causes melting.
this happens in regions called hotspots.
they do not cross much thus very little melt.
39
explain the effect of adding water has to the geotherm and thus the amont of melt.
The solidus is dependent of the material.
If we have ~3% water it changes the composition of the material thus changes the line.
However as the melt raises to the surface, it takes the water with it thus the melting system returns to its original state.
Water is normally pulled down in subduction zones.
40
explain the effect of reducing the pressure on the geotherm and thus the amount of melt produced.
Reducing the pressure allows the lines to cross.
When we pull the plates apart we make a hole.
This lowers the pressure which causes the melt, the melt is buoyant thus floats to the top and fills the gap.
41
explain/ describe the prosesses happening at a mid-ocean ridge.
When we pull the plates apart we make a hole.
This lowers the pressure which causes the melt, the melt is buoyant thus floats to the top and fills the gap.
It causes stripes in the rocks.
When it freezes it has a different composition to the mantle as it forms the crust.
42
what can we do to lead to even more melt then using just the normal processes and then use this to explain why iceland is part of oceanic plate and not continental.
We can combine two melting processes together. Normally this would be hot and low pressure. This will lead to more melt.
This causes Iceland to be part of the ocean. It is anomaly very hot and low pressure thus it protrudes above the sea due to isostaty as crust is much thicker ~ 35km.
43
why is the average calculated density of the earth greater than the average density of rocks found in the crust.
what can we infer from this?
the density of rocks in the mantle and core is much greater than that found in the crust.
its has a very high density due to the increase in pressure thus a decrease in voloume.
44
where is the transition zone?
the transition zone is between the upper and lower mantle. this depth can vary around earth.
45
what is the deepest place to see earthquakes?
**the transition zone** is the deepest point that we can see earthquakes.
46
if p waves cant travel through liquids, how can we image the inner core?
When a p wave hits the boundary between the lower mantle and the liquid outer core it can change to s waves thus we can image the inner core.
47
what is the process for the changing of the magnetic field?
The magnetic field doesn’t flip. The field shrinks and then grows in the opposite direction, this happens relatively quickly compared to geology time scale ~100 year.
48
radioactivity causes heat. what other way in the core creates energy?
The outer core is slowly freezing. When it freezes it falls down to the inner core, the iron and nickel freeze but the oxygen and sulphur don’t as they freeze at a much lower temperature.
These iron and nickel crystals that fall also creates energy.
49
what are the proportions of the earth made up of in terms of mantle and core?
mantle ~2/3
core ~1/3
50
in proprtion to other space objects what are sizes of the outer and inner core?
outer core is about the size of mars
inner core in about the size of the moon
51
what happens to waves that hit a boundry between two materials with different boundaries?
the waves get refracted.
52
describe p-waves
Compressional (or primary) waves
Alternately compress and dilate
Travels through solids, liquids and gases
Fastest seismic wave
Longitudinal
53
describe s-waves
Shear (or secondary) waves
Change in shape (no change in volume)
Slower than p-waves
Transverse
Particles move up and down not side to side
54
how can we use s-waves to find the size of the core?
s-waves can not travel through the core thus leaves a shadow on the opposite side of the earth.
the primary observation is that the outer core, if not the whole core must be liquid.
55
describe the low-velocity core p-wave shadow.
partial shadow zone
lower velocity in the core so wave is refracted
56
most of the mantle is made up of...
solid magnesium silicate
57
most of the crust is made up of...
metal silicates
58
which element dominates most rocks on earth?
Oxygen dominates – most rocks have oxygen in them
Oxygen has a large volume due to electron repulsion while other elements have less electrons so are attracted towards the centre thus less volume.
59
what is silica composed of?
silica - oxygen and silicon
60
what is silicate composed of?
silicate - oxygen silicate and a metal
61
how is the inner core solid while the outer core is liquid?
the inner core has a higher temperature however it is solid due to its very high pressure.
62
what is the magnetosphere?
the region surrounding an astronomical object such as the Earth, in which charged particles are trapped and affected by the object's magnetic field
63
**inside** the magnetosphere it is dominated by \_\_\_\_\_\_\_\_\_
**Inside** the magnetosphere it is dominated by **the Earth’s magnetic field**
64
**Outside** the magnetosphere it is dominated by \_\_\_\_\_\_\_\_\_
**Outside** the magnetosphere it is dominated by **the solar wind/ sun**
65
how can a compass be used to find the latitude?
Inclination is related to (magnetic) latitude
Tan(inclination) = 2tan(latitude)
66
what is detrital remanent magnetization?
67
describe chemical remanent magnetization
68
describe termoremanent magnetization
69
describe the effect of the currie temperature on thermoremanent magnetization
above the currie temp. the rocks cant not hold a magnetic trace.
below it the rocks can hold a magneti trace.
if the temperature is raised again, close to the currie temp. but not above it, then the rock will hold a finger print of past magnetization which we can the observe. as soon as it raises above the currie temperature, all the fingerprints are lost.
70
describe the magnetic traces of mid ocean ridges. and what do these traces allow us to do?
* Magnetic anomalies measured at sea
* Magnetic stripes on the ocean floor
* Symmetric about mid-ocean ridges
* Allows identification of past plate boundaries
* Allows dating of sea floor
71
explain reasons for why the graph line is curved and not straight lines that you would expect for a quick change in poles.
* As the plates flow it smudges the rocks thus a more rounded graph
* Also the top crust will cool down quicker than the bottom of the plate so reaches below Currie temp. quicker and in this time difference the plates will have moved so again we would not have perfect straight lines on the graph
72
what is internal and external heating and about how large are their values?
internal heating is heating from inside the earth (0.06W/m2)
external heating is from out of space,
e.g. the sun (342 w/m2)
73
if the sun has more sun spots, what can we say?
the more sun spots on the sun the cooler it is.
74
what are the three major causes of changes in the environment?
change in plate tectonics
change in earths orbit
change in suns strength.
75
about 50% of electromagnetic radiation from the sun is?
infrared
76
about 41% of the electromagnetic radiation from the sun is?
visible
77
of the 342 Wm-2 incoming from the sun how much is absorbed and reflected?
30% is reflected
70% is absorbed
78
we can measure the heat radiated back to space using satellites.
if the heat in is equal to the heat out what can we say about the temperature of earth is?
the temperature is fixed.
79
if there was no green house effect there would be no\_\_\_\_\_\_\_\_
if there was no greenhouse effect there would be no biosphere
80
what are the two important green house gases?
water vapour (changes dynamically)
carbon dioxide
81
all bodies above absolute zero radiate heat.
peak wavelength is inversely proportional to \_\_\_\_\_\_\_\_\_\_
peak wavelength is inversely proportional to temperature.
82
what is most carbon on earth stored as?
stored as carbonates/ organics in sediments and rocks.
83
how does the deep ocean have large amounts of carbon?
its so deep that there is a slow equilibrium between atmosphere and deep ocean.
84
what is the relationship between carbon dioxide and the ocean mixed layer?
ocean mixed layer and atmosphere are in equilibrium.
when we add carbon dioxide to the atmosphere it goes into the ocean mixed layer.
85
what is the effect of latitude on radiation absorbtion?
at high latitude:
less radiation per square metre of surface
more scattering in atmosphere (further distance to travel through atmosphere)
more reflection at surface
86
a ball being thrown at the equator to the north pole. it has a vector in the east direction of 500m/s thus the ball will curve even though the ball looks like it has been thrown straight.
how?
it is actually the earth/person that has moved. the ball is still going in a straight line.
87
in a low pressure atmosphere, the \_\_\_\_\_\_\_\_force and _________ force are in equillibrium, so winds go round and round.
in a low pressure atmosphere, the coriolis force and pressure force are in equillibrium, so winds go round and round.
88
density of water vapour is less than gasses so rises.
warm air rises
thus
dry air \_\_\_\_\_\_
cold air \_\_\_\_\_\_\_
density of water vapour is less than gasses so rises.
warm air rises
thus
dry air drops
cold air sinks
89
describe how a hadley cell works.
**Hadley cell**
* solar heating in the tropics makes warm air - increases evaporation
* warm, wet air rises, cools, rains, move to higher latitudes
* sinks in subtropics, ~30º latitude, warms, dry, no rain
* low pressure where rising, high pressure where sinking
90
what are surface ocean currents based on?
they work by shifting heat from the equator to higher latitude.
91
how can ocean currents vary with depth?
due to there being different densities and salinities. thus it forms layers in the ocean.
warmer = smaller density so near the surface.
**salinity**
evaporation
ice
rivers (add freshwater)
92
what is the effect of the ice caps?
they insulates atmosphere from warmer ocean thus organisms can survive in the ocean.
93
due to jupiter the eccentricity of the earth and sun changes every 100,000 years. what effect does this have?
as we get closer to the sun the earth gets warmer.
94
at higher latitudes, ice is stable at lower\_\_\_\_\_\_\_\_
at high latitudes, ice is stable at lower altitude.
95
what are the three major causes for changes in temperatures, other than humans.
eccentricity (100,000 years)
tilt (41,000 years)
precession (23,000 years)
96
what does precession tell us?
precession tells us which hemisphere will have a warm summer/ cold winter (links tilt and eccentricity)
97
what does tilt show us?
the larger the tilt, the more dramatic the seasons.
98
what does eccentricity show us?
high eccentricity means greater extremes as the earth gets closer and then futher away from the sun.
99
what are milankovitch cycles?
gr0wth/shrinkage of ice sheets linked to summer insolation.
affects many other processes:
- monsoons
- ocean circulation
- greenhouse gasses
this causes layers in the rocks as changes in tilt etc causes changes in evnironments.
100
describe how weathering leads to a negative feedback in terms of temperature and carbon dioxide levels
the negative feedback means that a balance/equillibrium is kept.
101
what is the effect of weathering of silicate rocks have on carbon dioxide levels?
weathering of silicate rocks (limestone) leads to carbon dioxide being **removed** from the atmosphere.
102
what happens to land after the ice on top of it melts?
after the melt the land level rises as a isostatic response.
103
why does vostok have great icecores?
the ice is deep so large record
its away from the sea so there are no change to the ice
104
what can you measure in ice cores?
dust levels
- shows how dry/windy it was
carbon levels
105
how can we measure temperaure change with icecores?
seen by isoptope of H2 called deuterium. deuterium freezes at a lower temperature than water with hydrogen.
106
how does ice volume relate to temperature?
we can look at ratio of C-16 to C-18 which realates to volume and temperature
107
first ice rafting was 2.75Myr ago.
what is ice rafting?
glacia picks up rocks from valley
forms iceburgs and floats out to sea
melts and drops rocks
found in sediments
108
cycles in temperature are dependent on earth and its milankovitch cycles (tilt, eccentricity, precession)
which cycle dominates through time?
it isnt one cycle that has dominated. the dominant cycle has changed through time.
109
as ice sheets get larger sea level \_\_\_\_\_\_\_\_\_\_
as ice sheets get larger sea level drops
110
what are the three causes for sea level rise?
co2 levels
tectonics
more mid ocean ridges
111
explain how more mid ocean ridges lead to an increase in sea level
they displace water forcing it to go on land
most mid ocean ridges have been subducted thus sea level is low compared to history
112
as we go back in time our data gets less \_\_\_\_\_\_\_\_\_\_
as we go back in time our data gets less accurate
113
we are currently in an __________ interval within a longer term ________________ climate
we are currently in an interglacial interval within a longer-term ice-house climate
114
what do you need at the poles for it to be a glacial period.
for it to be a glacial period you need a large continent at the pole.
115
what is the faint young sun paradox?
billions of years ago the intensity of the sun was about 0.7 of what it is today. thus we would expect that the temperature in the past to be -20º (with greenhouse gases) to -35º (without greenhouse gases)
however it cant be these temperature as there is evidence of life and liquid water.
thus temperature must be above the expected.
116
explain how the faint young sun paradox is wrong.
though there was weaker solar radiation there is a much stronger greenhouse radiation.
then as life evolves co2 is removed from the atmosphere
eventually the solar radiation will be so great that it will boil the earth even without the greenhouse effect.
117
co2 levels are measured in hawaii, why?
hawaii is away from factories thus wont disturb the sensors/data
118
explain the waves in the picture.
the biosphere is shrinking and expanding anually
trees take in co2 then drop leaves thus putting co2 back into the atmosphere
these waves happen differently depending on which hemisphere due to diffences in seasons
119
what are some of the major green house gases?
CO2 (40%)
CH4 (8%)
NO
O3
CFCs
water vapour
120
what two greenhouse gases have increased massively in the last centuary?
carbon dioxide and methane (increase in wetlands, rice)
121
about 10cm from melted ice leads to a \_\_º change in temperature of the ocean. this leads to the ocean \_\_\_\_\_\_\_\_\_\_\_
about 10cm from melted ice leads to a **1º** change in temperature of the ocean. this leads to teh ocean **expanding.**
122
describe the ranges of global temperature change on earth.
climate change is not the same everywhere
larger change on land than on sea
effects are larger in north than the south
effects at high latitudes are greater than a small latitude
some parts are getting colder
123
compare the northern and southern hemisphere ice sheets shrinkage and expansion.
**nothern hemishere**
ice sheets shrinking at around -13% per decade
**southern hemisphere**
ice sheets are expanding at about 0.9% per decade (smaller magnitude than northern)
124
why is antartica not shrinkig like the notrhern hemisphere sheets?
antaritica is surrounded by an ocean current which protects it as little can get across.
125
what is the **qualitative** evidence for continental drift?
**continental margins** match (better than matching coastlines)
matching **fossils** (a particular fossil is found only in south africa and south america, thus they must have once been together)
matching **rock types**
matching **mountain belts** (direction, age of mountain belts are of similar ages)
matching **glaciations** (you can see the direction of glacial movement through tills, thus showing the movement and starting point of continents)
126
what is the **quantitative** evidence for continantal drift?
**long base interferometry** (with quasors - mentioned in past presentation usin radio telescopes)
**GPS** - trilateration technique shows small scale movement of plates
**palaeomagnetism** (rocks take magnetic pole, the plates move and thus the rocks are no longer facing the north pole) ( there is also the fact that certain things like reefs and evaporites have a magnetism and you would expect them to be at the equator. however where we find them is not. thus plate movement)
127
what is the quantitative evidence for sea floor spreading?
magnetic stripes (its known that each side of the ridge has a trace of magnetic stripes, we know how often the poles switch thus can work out the age of the rocks dependong on how far away from the ridge it is)
128
what is the only difference between asthenosphere and lithosphere?
the only difference between asthenosphere and lithosphere is temperature.
thus lithosphere thickens away from the ridge - cooling transforms asthenosphere in to lithosphere.
129
what are the changes in thickness of oceanic crust from the ridge?
oceanic crust is formed at the ridge, and maintains **constant** thickness.
130
interms of the mid ocean ridge what is the realtionship between subsidence and age and distance?
subsidence is proportional /age and /distance(if speed is constant)
thus you can work out a fossils age by how far away it is from the ridge and how deep in the water it is.
131
explain how eathquakes will form at the fracture zones. even though fracture zones are inactive?
one side will subside more than the older side due to being closer and hotter thus will subside quicker.
thus can cause earthquakes
132
how are lines of sea mounts evidence for plate movement?
hotspots create seamounts but they move very little unlike the seamount trail. thus we can say that the hotspot plume is moving very little but it is the overlying plate that is moving.
we can then calculate velocity and movemnt of plates
hawaii is a good example of this. (the bend in the hawaii chain shows a change in direction of the plate)
yellow stone is also a hotspot track (erupts every 500,000 years)
the hot spots on africa dont form much in the way of chains as africa is pretty stationary (thus makes a good reference point)
133
briefly descibe the stages of a hotspot
meltin only occurs within \<~200km of the surface
motion at greater depth is flow in the solid state.
134
describe the process at mid ocean ridges
lithosphere is pulled apart
asthenosphere upwells to fill the space (responses to the pulling apart not the cause)
decompression - partial melting (20-30%)
melt forms new low density oceanic crust
high temperatures near surfce thus:
high heat flow so greater volume, thus
reduced density so floats higher thus
shallow bathymetry
135
describe the process of an evolving ocean basin
shallow asthenosphere cools thus
new lithosphere is formed
sea water circulates through crust thus
shemistry and temperature modified
cooling continues away from ridge thus
- density increases
- lithosphere thickens
- subsidence
- heat flow reduces
136
describe the process of subduction
thick, dense, old, cold lithosphere subducts (continental crust is so thick 35km that its low density keeps the plate up)
down-going crust dewaters
wet melting in overlying mantle wedge
melts form island arcs or andean volcanics
low density crust --\> high density eclogite (high pressure --\> when crust is pulled down to 100km its chemistry changes (metamorphic changes)(like granite to diamond)
subduction continue to at least 660km depth
scraped off sediments form accretionary wedge
137
what is the effect of gravity and heat have on earth in terms of rocks?
gravity tries to attract and compress
heat tries to disperse and expand
thus
gravity tends to sort by density and to form layering (densest in the middle)
heating tends to disrupt layers
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
temperature disequilibrium produces density variations
gravity performs on these, generating motion (lets high density fall, low density rise)
138
name a place where you can find earthquakes other than plate boundaries
hot spots
139
why doesnt water boil in submarine eruptions?
the high pressure prevents it.
the hot water just rises taking particles with it.
140
how are black smokers produced?
water petrudes crust when pillow lavas are created
dissolves various chemistry
heats and rises
precipitates out dissolved chemistry as black smokers
some organisims thrive of this
141
describe life a a black smoker
some organisms thrive of the black smokers
they utilise chemical imbalances produced by the black smokers
life here is **independent** of photosynthesis as there is no life.
142
if an accretionary prism sticks out of the sea enough then land can be made.
how does the younging direction work on a accretionary prism?
slices get younger at the bottom
143
where does the phase change happen on a down going slab?
lots of water leaves causing melt (water raises to surface with a signature in the rock made)
this leads to a phase change in the down going slabs 'crust' this then has gabbro and basalt change to eclogite which has a higher density
144
what process leads to back arc extension?
slab "roll-back" can lead to back-arc extension
this happens when the asthenosphere moves out of the way of the plate as the slab falls down wards and then goes around the slab, making space for the falling slab
this is most active in shorter arcs since displaced asthenosphere must flow out of the way.
145
roll back causes what to the shape of the trench?
roll back causes curvature of the trench
146
what happens if back-arc extension is too fast?
can produce a back-arc basin with sea floor spreading.
if so fast it can rip the slab making the back-arc basin
147
what does a steep subduction indicate?
steep subduction means the plate is much older, colder, and denser.
148
what are the two types of deformation of crystalline solids?
**elastic** - reversible as long as strain is small
**an-elastic** - irreversible when strain is very big
149
what is brittle failure and what is it normally associated with?
its when individual grains are broken
earthquakes normally involve brittle failure
occurs with quick release of energy
150
what is ductile flow?
it gets energy to break bonds from thermal energy
individual grains recrystallise
flow involves the diffusion of crystal defects
the defect moves through crystal forming a new crystal and flowing at the same time (behaves like a fluid)
151
compare brittle and ductile failure
**brittle (near the surface)**
low temp
low pressure
high stress
rapid deformation
**ductile (deep in earth)**
high temp
high pressure
low stress
slow deformation
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earthquakes involve brittle failure so in cold conditions.
how can earthquakes be found deep in the mantle?
cold is normally shallow, with the exception of subduction zones where it can be cold at deep.
away from subducting slabs, earthquakes are almost all confined to the crust
153
where would you find large compressional (thrust) faults, extensional faults, and compressional faults in a subduction zone?
large compressional (thrust) faults where the plates meet (in the accretionary prism
extensional faults in (shallow) slab from "slab pull" (as the plate bends downwards)
compressional faults in slab from "slab resistance"
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where would you find the deepest earthquakes?
660Km
155
give a reason why a subducting slab would break in half?
thick crust is light so wants to flow high.
slab isnt enough to pull it down so the slab breaks
156
describe the processes of continental formation
by creation of island arcs
by creation of other exotic terrains (means not a simple continent e.g. iceland)
by addition at andean-type margins
by hot-spot magmatism (if sufficently large - hawaii)
157
explain how seamounts can add to the continental plate
as a plate with sea mounts is being subducted the sea mounts are too large to be subducted so are scrapped off on to the continental plate
158
explain how the continental lithosphere often does not behave as a strong rigid plate
mantle is stronger than crust
cold rocks are stronger than hot rocks
thus
the strongest part of the ocean lithosphere is the mantle immediately below the crust
in the continents, this strong cold mantle is replaced by weaker crust
therefore continental lithosphere often does not behave as a strong rigid plate.
159
describe process that lead to continental breakup
continental lithosphere is weak
continents surrounded by subduction zones can be pulled apart - further weakening
breakup can be triggered by sub-continental hotspot
new ocean is formed
wilson cycle
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describe the wilson cycle
large continent
breakup
sea-floor spreading
large ocean
subduction
ocean closure
continental collision
large continent
161
compare continent and ocean crust and lithosphere
continental crust
thicker
more radio active
typically older heterogenous highly tectonised
more felsic (silicon)
continental lithosphere
weaker
often thicker (thus older)
more buoyent (thick low-density crust prevents continental lithosphere from subducting)
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what is the difference in continental and oceanic lithosphere?
lithosphere is thinner below oceans
163
the solar system is made of 8 planets 4 _____________ and 4 \_\_\_\_\_\_\_\_\_\_\_
the solar sysystem is made of 4 small solid planets and 4 large gaseous planets
164
there are 80 billion galaxies in the observable universe.
what is meant by observable universe?
what we can technically see. not what we really see
165
around how old is the solar system?
4.6 Gy old
166
around how old is the universe?
13.7 Gy old
167
around what is the diameter of the galaxy?
~100,000 light lears in diameter
168
the observable universe is ~93 Gly in diameter. how can we then see this if earth is not as old as this?
we can see this as the universe is exoanding thus light was sent closer and the object then moves away.
169
the sun has 99.9% of _______ of the solar system
the sun has 99.9% of the mass of the universe
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what controls the shape of the sun?
the shape pf the sun is controlled by the magnetic field
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the sun looks granulated. why?
the sun looks granulated due to small convection currents
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what is weird about the suns spin?
the equator spins a different speed to the polar regions
173
around what is the ratio of hydrogen to helium in the sun. what does this tell us?
hydrogen ~ 3/4
helium ~ 1/4
this ratio is about the same as the primordialratio of the two gases. thus very little has been converted
174
the sun is white hot but we see it as yellow. how?
the atmosphere makes it look yellow
175
what is the densest object in the solar system?
earth
176
how long till the sun turns to a red giant?
~5 billion year
177
briefly describe mercury.
looks like the moon
inactive --\> solid core
lots of crators
no atmosphere
remenent magnetic field --\> thus dead now
178
what is the caloris basin?
its a large crator on mercury.
the collision was very close to destroying mercury
179
describe venus
similar to earth (dimensions, close to earth, atmosphere)
cant see through the atmosphere with visible light
rotates very slowly
surface temp ~460ºC
~ 90 atm
few impact crators --\> young, active planet
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which planet rotates the opposte way to all the other planets?
venus
181
how can we see through venus' atmosphere?
we use radar.
some minerals reflect it more than others.
more old reflect it more
however the old rocks have been covered by dust thus the dark bits are actually the old rocks
182
the wind on venus is always in the same direction.
how do te impact crators on venus give evidece for an atmosphere? how do we use this to find the direction and speed of the winds?
when the collision happens dust is blown up in the air. this dust is then blown in a certain direction. as it is in a certain direction we can say the wind can only be in one direction,
by how far the dust blows shows us we can work out a wind speed.
183
how is venus so hot?
water on venus dissociates giving O and H2. the H2 left the planet as it is very light and the oxygen oxidised the carbon giving CO2 thus a very large green house effect.
being close to the sun has very little effect.
184
what is venus' tallest volcano?
Maat mons
185
what are rilles?
these are scars that have cut down into the rock.
formed by the low melting point of some igneous rocks. (molten carbonates)
186
what are pancake domes?
lava - mafic --\> low proportion of silicon
high viscosity
187
venus acts alot loke earths ocean. the closest to acting lke the continents is the \_\_\_\_\_\_\_\_\_\_
venus acts alot loke earths ocean. the closest to acting like the continents is the Tesserae
188
what does the moons far side look like?
older, rougher, further from centre --\> moon is assymetric
lots more crators
189
what are the unique features of earth?
plate tectonics
liquid water
oxygen in atmosphere
moon --\> large compared to planet (other moons are small compared to its planet)
has life
190
describe mars
smaller than earth (thus cant hold atmosphere)
massive canyon system (likely caused by water)
surface is dominated by sedimentary processes
191
what is the largest volcano in the solar system?
Olympus mons (Mars)
192
describe the polar caps of mars.
south pole has small ice cap of frozen CO2
north ice cap also has frozen water aswell
193
what is the evidence for some form of weak wind system on mars?
there are martian dunes.
they have a particular shape
there are also dust devils
194
martian moons, phobos and deimos, spin around mars faster than mars rotates?
gravity is pulling it towards mars
there will be an impact in ~50million years
195
how does the asteroid belt keep its shape?
the asteroid belt is gravitationaly stable due to the size of juipiter.
jupiter, the trojans, and the sun make an equilateral triangle 60,60,60
196
between what planets is the asteriod belt?
mars and jupiter
197
describe juipiter
very large
acts like a fluid --\> moves at different speeds
theres a storm system thats been there for over 300 years
198
how can we see the coriollis effect on jupiter?
two winds running past each other at different speeds creates these curvatures in the atmosphere
199
describe Io.
has different colours due to differences in temperature and chemistry.
its active with plumes of volcanic material being ejected
200
what is the most active object in the solar system?
where does it get the energy from?
Io is the most active object in the solar system e.g. a volcono appears in just six years.
it gets its energy through tidal temperature.
201
what is tidal temperature?
Io gets closer and further away from jupiter. this causes expansion and ompression of Io due to gravity.
this causes Io to heat up.
--\> a soild will heat up if you compress and expand it due to friction
202
describe europa.
very smooth H2O ice
subterranean liquid ocean
things come to the surface and freeze the break up
also gets tidal heat like Io. (the heat escapes through convection of water, thus not as hot as Io)
203
describe saturn
large
rings and small moons
204
whats saturns major moon?
titan
205
whats special about titan?
its a moon with an atmosphere
(droplets of metane and ethane make up the atmosphere)
206
describe titans surface
blocks of frozen hydrocarbons (methane)
drainage routes. shows active weather system
dont know what the energy source that drives the weather system as sunlight is not enough)
207
whats special about uranus
all other planets spin axis is perpendicular to plane of orbit.
uranus' spin axis is in plane of orbit.
208
what is the outer most object of the solar system?
neptune
209
what it one of the reasons that pluto is no longer a planet?
the centre of mass between pluto and its moon, charon, is not insid pluto but rather between the two objects.
thus pluto is not a planet
210
what do short period comets tell us about it?
short period comets are trapped inside the solar system.
211
what direction does the tail of a comet point?
it points away from the sun
212
what is the Oort cloud?
its material from the big bang that just hangs around a star
213
describe briefly how life forms on a planet?
once the planet is stable, life appear rapidly.
advanced multi-cellular takes billions of years to evolve
intelligent life takes another half billion years
214
where else in the solar sstem could we find life?
mars, europa
215
how are most exo-planets found?
most discoveries through doppler shifts of spectral lines
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