Module 1 - Earths Structure Flashcards
1
Q
Which planets make up the Terrestrial planets?
A
Mercury, Venus, Earth and Mars
2
Q
What are the characteristics of the Terrestrial planets?
A
- Few moons
- Bigger densities
- Closer to the sun
- Similar compositions
3
Q
Which planets make up the Gas Giants?
A
Jupiter, Saturn, Uranus and Neptune
4
Q
What separates the Terrestrial planets from the Gas Giants?
A
The Asteroid Belt
5
Q
What is the Asteroid Belt?
A
Fragments of carbonaceous, silicate and metallic material.
6
Q
How long ago was the universe created?
A
14 billion years ago
7
Q
What is the Big Bang?
A
The Big Bang led to the formation of the universe. It was the point in time when all matter and energy was created. At that moment, all matter was compressed into a space billions of times smaller than a proton.
8
Q
When and how did the solar system form?
A
- 4500 million years ago
- formed when a giant molecular cloud of gas and dust collapsed (the nebula hypothesis)
- the material eventually formed a rotating disc and as material was draw towards the center, nuclear reactions were triggered resulting in the formation of the sun
9
Q
Facts about the exploration of Earth’s Moon
A
•first landing mission - 1969
•apollo missions bought back 20kg of rock and soil dating to 4400 Ma
•the moon has a solid crust, mantle and core
•surface is made up of…
-the Maria - dark areas made from basalt lava flows (caused by impacts from meteorites)
-the highlands - light colored areas composed of plagioclase-rich rock anorthosite
10
Q
Exploration of Mars
A
- 1960 space probe Mariners 3-7 flew by taking many pictures
- identified Olympus Mons - the largest volcanic structure in the solar system
- 1970 and 2005 put space craft in orbit for longer
- 2007 space craft landed on the surface to move around and explore
11
Q
Exploration of Venus
A
- similar in size, mass, composition and distance from the sun to earth
- Venus has no oceans and covered by thick, rapidly spinning clouds that trap surface heat, creating a greenhouse like world with temperatures hot enough to melt lead
- the clouds reflect sunlight, making it the brightest planet in our sky
12
Q
Define the Solar System
A
The solar system is the Sun, planets, their moons, comets and asteroids
13
Q
What is the Sun?
A
The sun is a star composed of hydrogen and helium. It is the largest object in the solar system and contains more than 99.8% of the total mass
14
Q
What is a planet?
A
A planet is a sizable object orbiting a star
15
Q
What is a moon?
A
A moon is a natural satellite orbiting a planet
16
Q
What are asteroids?
A
Asteroids are rocky objects which failed to form a planet.
•ceres is the largest Asteroid with a diameter of 914km
17
Q
What are meteorites?
A
They are fragments of rock, which fall to earth from space.
18
Q
What is a comet?
A
A comet is composed of ice and dust. The outer layer melts into water vapour as it gets closer to the sun
19
Q
Where do most meteorites come from?
A
The Asteroid Belt
20
Q
What are the main types of meteorites found?
A
Iron and stony meteorites
21
Q
What are Iron Meteorites?
A
- composed of an alloy of Iron and Nickel
- makes up 6% of known meteorites
- thought to represent the core of a small planet
22
Q
What are Stony Meteorites?
A
- composed of silicate minerals (olivine/pyroxene/plagioclase feldspar)
- 93% of known meteorites
- thought to represent the mantle of a small planet
23
Q
What are Carbonaceous Chondrites?
A
A type of stony meteorite which contains water and organic compounds (similar in composition to the sun)
24
Q
What is the evidence for impact craters?
A
- you can see craters
* the moon has lots of impact craters and so would the earth if not for weathering and erosion of the earths surface
25
How do craters form?
1. Material is ejected and quartz grains are violently shocked and even melted
2. Rock strata is tilted
3. Material at depth to be brecciated (broken up)
4. The ejected material falls back to earth inverted. The sequence of rock changes
26
Name one of Jupiter's Moons
Lo
(Causes Jupiters enormous gravity field)
(Lots of active volcanism)
27
What is the oldest rock found on Earth so far?
3800-3900 Ma
28
What is the method used to date rocks?
Radiometric dating - uses decay of radioactive isotopes
| •mostly use rubidium-87
29
Which two spheres make up over 99% of the Earth?
The central core and surrounding mantle
30
What is the crust?
A very thin skin of cold, solid and the least dense rock which cooled against the atmosphere
31
What are boundaries?
Layers that show the distinct changes in composition and or physical properties
32
What is the inner cores properties and depth?
* 6371~5100km
* Made from solid material due to the extreme pressure
* Both P and S waves pass through the inner core
* the composition is a mixture of Iron and Nickel
* density of over 12g/cm^3
33
What is the estimated pressure of the inner core?
3600000 atmospheres compared to the 1 atmosphere at the surface
34
Where and what is the Lehmann Discontinuity?
* 5100km
* changes from the solid inner core to the liquid outer core
* a zone of about 100km
35
The outer core?
* 5100~2900km
* liquid Iron and Nickel
* S waves can't pass through the outer core
* p waves slow down due to the reduction in rigidity
* lower pressure than the inner core allowing a liquid to exist
36
Where at what is the Gutenberg Discontinuity?
* 2900km
* change of metallic material in the core to a stony silicate material
* changes state from liquid to solid mantle
* p wave velocity decreases and S waves stop
37
The Lower Mantle?
* 2900~700km
* the lower mantle is solid because S waves can travel through it
* P waves increase in velocity at the increasing pressure because the rocks become more rigid (less compressible)
38
The Upper Mantle?
* 700~35km
* consist of solid silicates but they are less dense than the lower Mantle
* the main rock is Peridotite
* partly lies in the asthenosphere and partly in the lithosphere
39
What two areas is the crust split into?
The oceanic crust and the continental crust
40
What's the difference between the oceanic crust and continental crust?
```
Oceanic Crust
•Rich in Fe and Mg
•Basalt-Pillow Lavas
•Dolerite-Dykes
•Gabbro in layers
•2.9g/cm^3 denisty
•oldest 200Ma
•average depth 7km
```
```
Continental Crust
•Rich in Al and Si
•Granitic rocks
•Igneous, Metamorphic and Sedimentary rocks
•2.7g/cm^3 density
•oldest 4000Ma
•average depth 35km
```
41
What is a Rheid layer?
A solid material with the ability to flow very slowly over millions of years
42
What depth do you find the temperature >1300 degrees?
75-670km but more specifically 75-250km
43
What is the Asthenosphere?
* The part of the Mantle with the ability to flow (where 5% of the crystals in peridotite are partially melted)
* shows plastic properties even though it is still a solid
* sometimes called the low velocity layer because P and S waves slow down
44
What is Peridotite?
An ultramafic igneous rock composed of the minerals olivine and pyroxene with a Coarse crystal size
45
What is Olivine?
A dense, ferrimagnesian silicate material
46
What is the Lithosphere?
The Crust and brittle rigid part of the upper Mantle
•where material is cool enough to prevent partial melting
•always rigid and brittle
•can't flow but is carried by the asthenosphere
•brittle so has broken into plates
47
What is Partial Melting?
Where a proportion of the minerals have a lower melting point, allowing them to melt while the rest remains solid
48
How deep does first hand observation of rocks allow you to see?
We can only reach rocks at about 2.5km which in total is the top 3.9% of the Earth. We can study the rock samples as they are actual physical evidence.
49
What can we find out from the analysis of surface geology maps?
What lies directly below the surface especially in areas where older crustal rocks are exposed from either earths movement or erosion
50
What do we mine for?
Coal, metal ores and Diamonds
51
What problems prevent us from being able to go very deep in mines
We can only reach about 4km in mines due to drainage problems, ventilation, high working temperatures and lifting the ore to the surface
52
How deep can we reach via boreholes?
* A depth of about 13km
* samples of rocks and microfossils can be bought up from boreholes and remote sensing
* Our deepest borehole is 23km
53
What is the Geothermal gradient?
It is the rate of increase in temperature per unit depth in the Earth.
54
What is the average geothermal gradient?
25 degrees/km
| However in volcanoes it can increase to about 30-50 degrees/km
55
What would happen if the rate of temperature change was constant?
All known rocks would end up melting
56
Why is the temperature gradient lower in the Mantle?
* Radioactive heat production is concentrated within the crust of the earth where elements such as uranium are found
* the mechanism of thermal transport changes from conduction to convection
57
How is Magma fesses to volcanoes?
Through vents that originate in the lower crust / upper Mantle
58
What is formed by partial melting of the upper Mantle at the MOR?
```
Basalt Lavas
(We can estimate the composition of the upper Mantle by analyzing these basalts and their volatiles)
```
59
What igneous materials can be occasionally found in volcanic pipes?
Diamonds and other minerals that have a compact crystal structure
60
What is the enclosing igneous rocks in volcanic pipes called?
Kimberlite after the Kimberley Diamond mine in South Africa
61
What are kimberlites?
Fine grained, ultramafic igneous rocks
62
What is an xenolith?
A fragment of 'foreign' rock included in an igneous rock which has come from a different source
63
What is an ophiolite?
A section of oceanic crust and upper Mantle broken off and attached to the edge of a continent during plate movement. Caused by the collisions of plates. This process is known as obduction
64
What is an ophiolite made from?
```
•sediment
•basalt pillow lava
•dolerite
•gabbro
•peridotite
(A complete cross section of the oceanic crust up to 7km thick)
```
65
What do we rely on to predict the structure of the earth?
Seismic waves, density data and meteorite evidence
66
What are seismic waves and how are they detected?
Vibrations caused by the movements of the plates and faults. They are what cause earthquakes and they are detected by seismographs all around the world.
67
What are P and S waves?
P and S waves are waves that travel through the layers of the Earth and so are called body waves.
•travel faster if the rock becomes more rigid and more incompressible
•slower if the rock becomes more dense
68
When do P and S waves change speed?
* asthenosphere they both slow down due to the reduction in rigidity
* both speed up in the Mantle as the pressure is increased and rocks become more incompressible
* P waves slow down at the Gutenberg Discontinuity as they enter the liquid and S waves stop
* P waves speed up at the Lehmann Discontinuity as they enter the solid (S waves are propagated at 90 degrees to the P waves)
69
What is the shadow zone?
The zone in which no waves were recorded
70
What are the angles that you get no waves?
P waves 103-142 degrees
| S waves 103-103 degrees
71
What is the average density of the Earth?
5.5g/cm^3
72
What is the density for each layer of the Earth?
Measured in g/cm^3
* continental crust- 2.7
* oceanic crust - 2.9
* upper Mantle - 3.4
* lower Mantle - 4.4
* outer core - 9.9
* inner core - 12.8
73
What are the densities of Iron Meteorites and Stony Meteorites?
Iron - 7.0-8.0 g/cm^3
| Stony - 3.0-3.7 g/cm^3
74
What is the origin of Earths Magnetic field?
* convection current occur in the outer core due to the high temperature
* a convecting mass of molten iron will generate electricity
* this in turn causes magnetism
* the balance between generation and destruction allows the Earth to show a weak yet continuous magnetic field (the dynamo effect)
75
The circulation of the convection currents is affected by the rotation of the Earth, what does this cause?
That the position of the magnetic poles are close to the geographic poles.
76
What does remanent magnetism provide evidence for?
That the convection in the core changes and this means that the magnetic field gradually fades over a period of several thousand years and then increases with the poles the other way round.
77
What are frozen compasses?
Iron rich minerals that have aligned to the Earths magnetic field and cooled through the curie point retain the magnetisation showing the direction of the Earths magnetic field at the time.
78
What do Aerial surveys show?
They show the reversals of the poles of the ocean floor basalts. Sensitive magnetometers show normal field strength over the zones of normal polarity.
79
What is Palaeomagnetism?
Ancient magnetism preserved in the rocks
80
What is a magnetic anomaly?
A value for the Earths magnetic field that is different from the expected value
81
What is magnetic inclination?
The angle of dip of the lines of a magnetic field. It is the angle with the horizontal made by a compass needle
82
What is Remanent magnetism?
Magnetism shown by rocks due to the alignment of their magnetic minerals according to the Earths magnetic field at the time of their formation
83
What is apparent polar wandering?
The evidence to suggest that the magnetic poles wandered all over the globe. The continents have moved creating a sense that the poles were in two places at once.
84
What six observations can we make to study the Earths structure?
* seismic activity
* rocks on the earths surface
* density of the earth
* study past and present volcanoes
* Meteorites
* magnetic field
85
What is the elastic rebound theory?
1. Undeformed rocks
2. Rocks deform due to the build up of stress
3. Rocks fracture and stress is released as seismic waves
An example is the San Andreas fault - a dextral tear
86
What is the composition of each of the Earths layers?
* oceanic crust - basalt and magnesium silicate
* continental crust - granite
* upper Mantle - silicon dioxide, olivine and peridotite
* lower Mantle - iron + magnesium silicate
* outer core - Nickel + Iron + Potassium + Sulfur + Silicon + oxygen
* inner core - Nickel, Iron alloy and Uranium
