All lectures Flashcards
(262 cards)
1
Q
Define homogeneous.
A
All the same/of the same kind.
2
Q
Is the chemistry of the cosmos homogeneous?
A
No, it is non-homogeneous.
3
Q
How deep does the abundant layer of the earth go?
A
25-30km.
4
Q
What % does the earths surface make up?
A
1%
5
Q
What are the two most abundant elements?
A
Hydrogen and Helium.
6
Q
What is most abundant, even or odd atomic numbers?
A
Even.
7
Q
What is the most logical starting element for the other elements to be formed from?
A
Hydrogen, it is the most abundant.
8
Q
How do stars form, what temperature does it reach during formation?
A
A cloud of interstellar dust and gas (90% Hydrogen) begins to collapse under gravity and heats up.
Nuclear fusion begins I(hydrogen burning)
This creates thermonuclear reactions at 5-10 million kelvin.
9
Q
How much hydrogen does the sun consume in a second?
A
600 million tonnes.
10
Q
What does the sun convert hydrogen into?
A
Helium.
11
Q
How much helium does the sun create every second?
A
595.5 million tonnes.
12
Q
4.5 million tonnes of energy is converted into what by the sun?
A
Energy.
13
Q
What happens once 90% of hydrogen has been consumed by by a star?
A
It will become a red giant then collapse to a white dwarf.
14
Q
How old is the sun?
A
Five thousand million years old, middle aged.
15
Q
What elements does helium burning/nuclear fusion produce?
A
Elements with a mass number that is a multiple of 4, which are increasingly higher atomic mass than the start material. E.g. 12C and 16O.
16
Q
What is the end of a stars evolution?
A
Supernova, a violent explosions.
17
Q
What do supernovae do?
A
Send the products of nuclear reactions into space, which are then incorporated into new stars.
18
Q
Is our star brand new material?
A
No, it is a second generation star at least, it contains chemicals that our sun is not yet producing.
19
Q
What is at the center of our solar system?
A
The sun.
20
Q
Do all the planets revolve in the same direction?
A
Yes.
21
Q
What direction do the planets rotate in?
A
The same direction as they revolve around the sun.
22
Q
How many planes do the planets revolve on?
A
A single plane almost.
23
Q
How far away are the planets from each other?
A
Each one is twice as far away as the last from the sun.
24
Q
What % mass is the sun of the atmosphere?
A
99.9%
25
What is the general density of planets in the solar system?
Denser in the center of the solar system and the large gas giants in the outer solar system.
26
Mars and Jupiter do not follow the same distance pattern as the rest of the planets in the solar system, why is this?
There should theoretically be another planet between them, there is the asteroid belt there instead.
27
What is a meteorite?
A solid extra-terrestrial material that survives passage through the atmosphere and reaches the surface of the earth as a recoverable object.
28
What are the three main classifications of meteorites? And sub-divisions.
Irons, stoney-irons and stones. Stones are divided into chondrites and Achondrites.
29
What does an iron meteorite contains?
90% metals (Fe + Ni)
30
What do stoney-iron meteorites contain?
50% metals.
31
What do the chondrite meteorites contain?
10% metals.
32
What do the achondrite meteorites contain?
1% metals.
33
Where do meteorites come from?
The asteroid belt mainly (some from the moon and mars)
34
What do asteroids represent?
Either a broken up planet or raw material for an unformed planet.
35
What are 3 facts about Fe meteorites?
They are dense and previously molten.
They are made of either Fe or Ni alloys.
Unlikely from a single parent body.
36
What is a better meteorite, fall or find?
Falls, finds have bias.
37
What is the most abundant meteorite? And what is the %?
Chondrites, 85.7%
38
Why are chondrites important?
They are very similar to the bulk earth chemistry so can be used as a comparison.
39
What are the three historical models for the earths formation?
Homogeneous hot, homogeneous cold and heterogeneous.
40
What are the 4 steps for the modern planet formation model?
1) Settling of the circumstellar dust to the disk.
2) Growth of planetismals (1km)
3) Runaway growth of planetary embryos (1000km)
4) Growth of large objects by late stage collisions.
41
What is radioactive decay?
Radioactive elements decay at a known rate, uneffected by temperature and pressure.
They all have a half life.
Radioactive parents decay into stable daughters.
42
On what sort of rate did the Earth form?
More than half formed in the first 10 million years, then the rate declined.
43
Have radioactive elements increased?
No, there was previously a higher abundance of radioactive elements. The short lived isotopes are now all gone.
44
How much hotter was the earth when radioactive elements were more abundant?
x 10 more heat.
45
What effect did early heating have on the Earths formation?
Iron melted, due to its density it sank to the middle.
| This iron releases its heat and creates the sea of molten rock around it.
46
What element being present may have lowered the melting point of iron in the earth?
Sulfer.
47
What was the iron catastrophe?
A mars sized object collided with the earth and may have caused the whole planet to remelt. This was called Thea.
48
What did the melting cause from the iron catastrophe?
The earth to no longer be homogeneous.
| Fe-rich hot core with a hot solid topped with a thin crust.
49
Is the bulk earth and the crust chemically the same?
No.
50
What elements make up 99% of the earths surface?
O, Si, Al, Fe, Mg, Ca, Na and K.
51
What is the most abundant element at the earths surface?
Quartz, SiO2.
52
Define mineral (4 things)
Naturally occurring,
homogeneous solid,
definite chemical composition
and ordered arrangement of atoms.
53
What is the chemical composition of feldspars?
O, Si + Al, Ca, Na and K.
54
What are the main mineral groups? (6)
Olivines, Pyroxenes, Garnets, Plagioclase feldspar, alkali feldspar and quartz.
55
What are felsic minerals?
Feldspar and quartz.
56
What is ferro-magnesian?
Fe and Mg.
57
What is the Gibbs phase rule?
F = C - P + 2
58
Explain all the elements of the Gibbs phase rule?
```
F = Degrees of freedom.
C = Number of components.
P = Number of phases.
```
59
What does degrees of freedom mean?
How many variables can you change while staying in the same phase.
60
Explain the number of phases part of the Gibbs phase rule.
For example the number of phases would be 2 at the boundary.
61
What is the Eutectic?
The lowest temperature a liquid can exist in a system, a lower temperature than either of the pure components.
62
What does divarient mean?
You can change one variable and it'll still be within the same phase.
63
What does univarient mean?
You can't change one variable without the other, or it will be within another phase.
64
What does invarient mean?
You can't change any variable without changing phase.
65
What is a unary phase diagram?
Shows changes of 2 variables, so only one component can be displayed.
66
What is a binary phase diagram?
Only one variable can be shown on this graph as two components are being shown.
67
What is the condensed Gibbs phase rule?
F = C - P + 1.
68
What is the condensed Gibbs phase rule used for?
Binary phase diagrams with two components.
69
Explain eutectic melting?
Partial melting occurs if the mixture is not 50/50 with the eutectic being at 50/50.
When it melts it leaves behind rocks of a different composition.
70
What is the unit for gravity?
Gal. Named after Galileo.
71
What is 1 Gal in m s^-2
10^-2 m s^-1.
72
Why is acceleration due to gravity not the same all over the earth?
Due to the earth rotating and not being a perfect sphere.
73
What is the shape of the earth?
Flattened at the poles with a bulge around the lower hemisphere.
Pear shapes oblate spheroid.
74
What is the geoid?
Mean sea level of the oceans. A reference surface.
75
What doe milligals measure?
Small gravitational variations due to rock type change.
76
What effects do large mountains have on the plumb line?
They deflect it, its attracted to the mountains.
77
What did Pierre Bouguer do?
Led an expedition in France to the Andes to measure the shape of the earth.
78
Mass below mountains is less than it was thought, what two people had what theories on this?
Airy's theory - There is a root under mountains.
| Pratts theory - Mountains have lower density rocks beneath them.
79
What is the free air correction?
It assumes there is nothing but air between the measurement height and sea level.
80
What is a free air anomaly?
If the gravity measurement isn't zero after the corrections, then there is a free air anomaly.
81
What is the Bouguer correction?
This allows for the gravitational attraction of rocks. If the result still isn't zero then there is a Bouguer anomaly.
82
What is a Terrain attraction?
This allows for the variation in surface shape unlike the Bouguer correction.
83
Give an example of an inverse square law.
Gravity follows this law.
84
What is isostatic equilibrium?
When there is no excess of mass above the compensation level. Corrected gravity has a reading of close to zero.
85
Doe Hawaii have a free air anomaly?
Yes, a strong one. This means it is not in isostatic equilibrium.
86
What do Bouguer anomaly maps show?
Where rocks are more or less dense than the average.
87
Where does isostatic rebound occur?
In eroding mountains, where the root is rising to the surface or in previously glaciated areas.
88
Examples of an area where fast isostatic rebound is occurring is?
Scotland is rising due to previously being glaciated, the north is sinking.
89
What is seismology?
The study of earthquakes.
90
What are elastic waves?
They are produced by earthquakes and called elastic as the rocks stretch and change shape but then return to the original shape.
91
What are the two different types of waves?
Body waves - through the solid earth.
| Surface waves - on the earths surface only.
92
What are three other names for p waves?
Primary, pressure or push-pull waves.
93
What are three other names for s waves?
Secondary, shear or shake waves.
94
What kind of wave is a P wave?
Compression.
95
What kind of wave is a S wave?
Twist.
96
Velocity of P waves is controlled by?
Rigidity, density and how compressible the rock is.
97
Velocity of S waves is controlled by?
Rigidity and density.
98
Which is faster, P or S waves.
P waves.
99
Can S waves move through liquids?
No.
100
Higher density has what effect on velocity?
Higher seismic velocity.
101
What type of wave does more damage, body or surface waves?
Surface waves.
102
What are the two types of surface waves?
Rayleigh and love waves.
103
What is the difference between Rayleigh waves and Love waves?
Rayleigh waves - up and down (ground roll)
| Love waves - side to side (shaking)
104
What is another word for the focus?
Hypocentre.
105
What is the focus?
The point within the earths surface the earthquake nucleated.
106
What is the epicentre?
The point on the earths surface the is vertically above the focus.
107
How are earthquakes located?
With at least 3 different seismic stations.
108
How do seismic stations work?
They measure in degrees, the time difference between P and S waves give the estimated angle of arc/distance.
109
How is the earthquake focus depth worked out?
By the time difference between direct P waves and reflected P-waves.
110
What is the Richter scale and what does it measure?
A logarithmic scale that measures the first arriving P wave.
111
When was the Richter scale first made?
1935.
112
What is a famous high measuring earthquake?
The great Chilean earthquake. 1960 and measured 9.5 on the Richter scale.
113
What measurement is used for energy?
Joules (J)
114
What effect other than velocity change does a change in density have on seismic waves?
Waves can be deflected.
115
At what degrees away is the S wave shadow zone?
103 degrees either side of the earth.
116
Why is there an S wave shadow zone?
There is a liquid layer reached which S waves cannot travel through. This is the core,
117
What is seismic reflection and what is it used for?
Reflected seismic waves used to detect changes below the surface. This is used in oil and mineral exploration.
118
At what degrees is the P wave shadow zone?
103 to 143 degrees. One shadow zone on either side of the earth.
119
What is a discontinuity?
A boundary between layers in the earth.
120
What is the name and depth of the core-mantle boundary?
Gutenburg discontinuity - 2900km.
121
What is the depth to the inner core?
5200km.
122
What is the depth to the outer core?
2900km.
123
Is the inner core solid or liquid?
Solid.
124
In the outer core solid or liquid?
Liquid.
125
What does the Moho discontinuity divide?
The crust and the mantle.
126
How deep is the Moho discontinuity below continents and below oceans?
Continents - 35km
| Oceans - 5-10km.
127
What changes as you pass the Moho boundary?
Rock mineralogy, state remains the same.
128
What are the mantle discontinuities named after?
Their depth.
129
What changes as you pass mantle discontinuities?
Mineralogy.
130
At what depths are the two mantle discontinuities?
390-410km.
| 670km.
131
What is the most abundant mineral in the mantle?
Olivine.
132
What happens to olivine as the depth of mantle increases?
The structure becomes unstable and the atoms become denser. This is called a phase change.
133
At what depth is the upper mantle?
Below the moho (which differs) and above 670km.
134
At what depth is the lower mantle?
Below 670km and above the core.
135
At what depth is the low velocity zone/layer?
Between 60-220km.
136
What is the lithosphere?
Crust and upper most part of the mantle.
Grouped due to their similar seismic activity.
NOT THE SAME AS THE UPPER MANTLE.
137
What is the asthenosphere and where is it?
This is the same as the low velocity layer 60 - 220 km. Below the lithosphere.
138
What does olivine turn into at the 390-410 mantle discontinuity?
Spinel.
139
What does spinel turn into at the 670 mantle discontinuity?
Perovskite.
140
What kind of change does olivine undergo as it gets deeper into the mantle?
Structural change.
141
What does the earths magnetic field protect us from?
Solar wind, this would strip away the atmosphere.
142
What is the name for the earths magnetic field?
The magnetosphere.
143
What is the curie temperature?
The temperature which magnetism can not exist above.
144
What is inclination?
The angle the magnetic field emerges from the surface of the earth, this changes with latitude.
145
What is declination?
The difference between magnetic north and true north.
146
Are the inclination and declination always the same?
No, they both change over time.
147
What do basalt lavas typically form?
Magnetite, a member of the spinel group and an oxide.
148
What use does magnetite have to geology?
When it falls below the curie temperature the crystals align with the earths magnetic field, this is then preserved when the rocks solidify. Basalts can be aged so the magnetism can also be aged.
149
What is normal polarity?
Present day polarity.
150
What is reversed polarity?
The reverse of present day polarity.
151
What are chrons?
Intervals of predominantly normal or reverse polarity.
152
How often does the earths polarity flip?
Generally over millions of years.
153
What are the last four chrons in order of most recent to least recent?
Brunches
Matuyama
Gauss
Gilbert.
154
When was the Brunches chron?
present to 780,000a.
155
When was the Matuyama chron?
2.6Ma - 780,000a.
156
When was the Gauss chron?
3.6Ma - 2.6Ma.
157
When was the Gilbert chron?
Pre 3.6Ma.
158
What is a superchron?
Long periods with no reversals.
159
Example of superchron?
Cretaceous 120-83Ma normal polarity.
160
Are polarity reversals random?
Yes.
161
What is the geomagnetic dynamo?
Electric current loops in the liquid outer core generated by movement of the molten material. This is a self exciting dynamo.
162
How do reversals occur?
If the current in the geomagnetic dynamo changes direction then the polarity will follow.
163
What would happen if the geomagnetic dynamo stopped?
It would take 60,000 years for the magnetism to go.
164
What is the % weakening of the magnetic field when polarity reversals occur?
10%
165
What is the minimum energy required for the magnetic field to be maintained?
5,000 megawatts.
166
Define convection.
Transfer of heat by transfer of mass.
167
Define advection.
Got materials physically moving, e.g. isostatic rebound.
168
What are the 3 possible sources of energy for thr magnetic field?
1) Thermal convection.
2) Compositional convection.
3) Primordial heat.
169
How thick is the inner/outer core boundary?
Only a few km thick.
170
Is there a large difference in the composition of the inner core and the outer core?
No, they are similar.
171
Why is K40 not the heat source for thermal convection?
There is only 1/3 left from the earths formation, so it is unlikely. A lighter element like sulfer may be possible.
172
What may be causing compositional convection in the core?
The crystallisation of the inner core makes the outer core materials more buoyant, this may cause the compositional convection. Latent heat from the crystallisation may also drive the convection.
173
What is primordial heat?
Heat left over from the earths formation.
174
Why is internal heat so important?
It is the driver of internal processes like volcanic activity.
175
Define conduction.
Movement of heat from high temperature to low temperature, no material is moved.
176
Define radiation of heat.
Heat moving as waves, no contact is needed.
177
Where within the earth does conduction occur most?
The lithosphere and the solid inner core.
178
How does convection occur within the earth when it is mostly solid?
Because over geological time it acts more as a liquid.
179
Where within the earth does convection occur most?
The mantle and outer core.
180
How important is radiation within the earth?
Not very important.
181
When was the first theory of continental drift?
1596.
182
Who first theorised continental drift and how was it explained?
Abraham Ortelius - Saw the match of South Americas coastline and Africas, torn apart by earthquakes and floods. 1596.
183
What was Wegeners contribution to the continental drift theory?
Linking geological features, fossils and mountain chains on both continents coastlines.
184
What was the first super continent called?
Pangea.
185
What was the name of the sea that surrounded Pangea?
Panthalassa.
186
What did Pangea first split into?
Laurasia and Gonwana land.
187
When was the first model of convection theorised?
1928.
188
Who first theorised convection and how was it received?
Arthur Holmes, suggested the plates moved but had little evidence and some faults in the theory. 1928.
189
When was the Challenger expedition?
1872-1876.
190
What was the challenger expedition?
Deep sea soundings and bottom dredges with led to the first systematic description of the oceans. 1872-1876.
191
Who came up with the first mappings of the topography of the oceans and depths?
John Francon Williams.
192
What was H H Hess' contribution to mapping the oceans?
During WW2 he kept the sonar running as he sailed a transport ship. This created profiles, discovering flat top volcanoes (Guyots). This was the discovery of sea floor spreading. 1906-1969.
193
Who and when was the North Atlantic Ridge discovered by?
Lamont-Doherty Earth Observatory of Columbia University. 1953.
194
Where else are ocean ridges other than the Atlantic?
In all oceans, but not all in the middle.
195
Who was magnetic polarity discovered by and when?
Manson, 1952.
196
Who first suggested that basalt recorded the flipping of polarity and when?
Vine and Matthews, 1963.
197
What was Wine and Matthews description of flipping polarity?
The new material at spreading ridges acts like a conveyor belt, this is proven by the symmetry on either side.
198
Why are the magnetic stripes sometimes offset?
Likely to be due to faulting, specifically transform faults.
199
What is an example of magnetic stripe offsetting?
Romanche Trench in the Atlantic.
200
Are the oceans relatively old or young?
Relatively young?
201
Where is the youngest ocean floor?
At the ridges, then progressively getting older as you move away from the trench.
202
What does the width of the magnetic stripes tell us?
Thicker stripes mean faster spreading.
203
Where does seismic activity occur? At what depth?
Ocean ridges - shallow.
The pacific ring of fire - up to 750km
Mountain regions.
204
Where are ocean trenches relative to seismic activity?
Some distance away.
205
Ocean trenches are some of the deepest parts of the ocean, which trench is the deepest?
Marinas trench.
206
How can we see oceanic material at the surface?
By studying Ophiolites,
207
What is a typical Ophiolite structure?
```
Deep sea sediment.
Pillow basalt/lavas.
Sheeted dykes.
Gabbros .
Layered peridotites.
Peridotites/dunites.
Un-layered mantle.
```
208
Give an example of an Ophiolite.
The Semail Ophiolite in Oman.
209
Early formed crystals in magma chambers settle to the bottom, what does this form?
Layered Peridotites and Gabbros.
210
What is the fastest spreading ridge?
The East Pacific Rise.
211
How much does the East Pacific Ridge spread in a year?
18.3cm.
212
What shape magma chamber feeds the East Pacific Ridge?
Onion shaped.
213
How do the plates move?
The asthenosphere/LVZ is soft so van creep. 60-220km.
214
What are the three types of plate boundary (Both names for each)
1) Constructive/divergent.
2) Destructive/convergent.
3) Conservative/transform.
215
Does convection drive tectonics?
No, this is more likely a drag.
216
Does ridge push drive tectonics?
The raised ridges may cause gravity to move the plates.
217
Does slab pull drive tectonics?
This is thought to be the major driver.
218
What is thermoremnent magnetism?
The stripes formed by iron minerals in basalt. This cannot be re-orientated.
219
What other ways is magnetism displayed?
Detrital remnant magnetism.
| Chemical remnant magnetism.
220
What is detrital remnant magnetism?
Fine-grained magnetic sediments settle in alignment with the earths magnetic field.
221
What is chemical remnant magnetism?
Magnetic minerals growing within a sediment align with the earths magnetic fields.
222
Why are dyke chilled margins at a ocean ridge different?
The dyke is split in the middle by a new dyke, so there is only a chilled margin on one side of each half of the original dyke.
223
Where may a plate be in the process of breaking up?
East African Rift Valley, there are volcanoes which may be the beginning of a ridge.
224
Where is the only place an ocean ridge rises above the surface?
Iceland.
225
What is continental crust made up of?
Granite.
226
Does continental crust ever get destroyed at a plate boundary?
No, there are much less dense so never submerge. The do erode however.
227
What are the two types of destructive plate boundary?
1) Oceanic lithosphere submerging under oceanic lithosphere.
| 2) Oceanic lithosphere submerging under continental lithosphere.
228
As you move away from trenches, the earthquakes get deeper. What is this called?
The Wadati-Benioff zone.
229
What is the typical angle of the Wadati-Benioff zone?
45 degrees.
230
Where do earthquakes occur in thrust faults?
60-100km.
| Within the slab due to dehydration reactions or phase changes at more than 300km.
231
What is an accretionary prism?
A build up of sediment along the destructive boundary, scraped off the oceanic plate and eroded off the overriding plate. Formed at thrust faults.
232
What is often trapped in accretionary prisms?
Resources like gas.
233
What is a passive margin?
Where there is no destruction, these show extensional faults as the plate submerges.
234
Name a famous transform fault.
San Andreas fault, California.
235
What is Peridotite?
Made from Olivine and pyroxenes, can be within the mantle.
236
What happens when mantle moves from high pressure to low?
It decompresses, but due to it being surrounded by equally hot magma it cannot lose its heat. This is called adiabatic decompression.
237
What melting occurs with adiabatic decompression?
Partial melting, it only occurs at the Eutectic. Once 10-20% melt of some magma occurs it splits from the solid and rises quicker.
238
What magma is formed from adiabatic decompression?
Basalt. A basic magma.
239
What is the composition of Basalt?
SiO2 - 50%
FeO - 10%
MgO - 7.5%
CaO - 11.5%
240
What is MORB?
Mid Ocean Ridge Basalt.
241
What causes the LVZ?
A small % of water in the mantle which lowers the rigidity.
242
What is obduction?
Ophiolite's coming to the surface.
243
How can we observe MORB layers?
From studying ophiolites.
244
Explain the creation of black smokers.
Water is drawn down into the hot oceanic lithosphere, this removes heat and dissolves metallic minerals.
This changes the rock with low grade metamorphism and the rocks are hydrated.
245
What are subduction zones marked by?
Arcuate chains of island arcs.
246
What happens to cold lithosphere as it subducts?
A steady increase in temperature and pressure.
Prograde metamorphism.
Dehydration reactions occur at 100km - this water rises and promotes melting.
247
What magma and rock is formed at subduction zones?
Calc alkaline magma.
| Andesite.
248
What is a back arc basin?
A small sea opening behind the island arc.
249
Where is thought to be a fixed point in the earth?
Hotspots.
250
Example of a hotspot is?
Hawaii.
251
What is a hotspot?
An area where deep hot mantle rises up, sometimes in the middle of a plate.
252
Explain how hotspots may move? How does this effect the age of islands?
The hotspot is thought to stay in place, but as the plate moves over it the island is youngest where the hotspot currently is and gets older as you move along the chain of islands.
253
What happens when a plate is being destroyed quicker than its being created?
The island arc will collide with the continent and the back arc basin will close.
254
What happens at continent to continent collision?
The crust crumples and thickens creating mountain chains, neither subduct.
255
What kind of fault occurs at continent to continent collision?
Thrust faults, they are compressional unlike normal faults.
256
Does decompression melting occur at continent to continent collision?
Yes, not always though.
257
What will happen when the mountains erode away?
The crust will rebound.
258
What kind of rock is formed at continent to continent collision?
Granite.
259
How thick is continental crust?
25-70km.
260
How thick is oceanic crust?
7-10km.
261
How thick is the lithosphere under the ocean?
50-140km.
262
How thick is the lithosphere under the continents?
40-280km.
