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LEC172 Lecture 12 & Understanding Earth Ch 7 notes
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Summary notes for Lecture 7 and UE Ch 4 - Volcanism & Plutonism – 2
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CH 1 – The earth systemA coherent set of hypotheses that explains some aspect of nature constitutes a theory. Yet a theory
can never be considered completely proved.
The geologic record is the information preserved in the rocks that have been formed at various times
throughout earth’s history
James Hutton set up the concept of the principle of uniformitarianism (the present is the key to the
past): the same natural laws and processes have always been the same throughout history.
Nowadays it is a bit too confining for geologic science as it is practiced.
Geodesy is a very old branch of earth science that studies earths shape and surface
Seismic wave causes earthquake
Highest point of earth (mt. Everest) 8850m and lowest point (challenger deep) 11.030m deep
Earth layers:
Crust 040km
Mantle 402890km (solid)
Outer core 28905150km (liquid)
Inner core 51506370km (solid)
Seismic waves can be used to study earths characteristics (2 types):
1. Compressional waves expand and compress when traveling through solid, liquid or gas
2. Shear waves which can only go through solids
Mantel boundary is put at 2890 because from this point an iron-nickel alloy can be melt but silicate
rock can not
The crust contain more aluminium an potassium (this boundary is called the Moho). The moho can
sometimes be about 7km in oceans but 40km beneath continents
Because of its density continent are buoyant on top of the denser mantle
The reason of the inner core being solid, while the temperature is higher is because of the higher
pressure
In the mantle there is also a density drop at 410 and 660 but are smaller than the main boundaries
Inner core is almost entirely an iron-nickel alloy
8 elements (out of up to a hundred) make up for 99% of earths composition: 90% iron, oxygen,
silicon and magnesium
Oxygen is more apparent at the mantle and not in the core, which is the other way around for iron
Earth has two heat engines:
1. Internal heat engine powered by the heat energy trapped in its deep interior during its
violent origin and released inside the planet by radioactivity
2. External heat engine solar energy
Open system exchanges energy and mass with its surroundings
,Earths climate system is energized by solar radiation, the plate tectonic system and the geodynamo
system is energized by the internal heat engine
The climate system consists of:
1. Atmosphere
2. Cryosphere
3. Hydrosphere
4. Biosphere
5. Lithosphere
Lithosphere is the top part of the mantle, which is on top of the asthenosphere, which is weaker,
flows and is moldable.
Convection is a processes that makes hotter materials rise and cooler materials sink. The plate
tectonic system works by convecting mantle prosses.
The geodynamo is the magnetic energy originating from the outer core. It is not a permanent magnet
because these are disabled at a temperature of 500degrees. It is theorized that it is constantly
generated. Why in the outer core?
1. It consist of iron which is a great electrical conductor
2. The flow is more rapid than the inner core or mantle, which stirs up electrical current
Earth formed 4.56 billion years ago by rapid condensation of dust (oldest rock found 4by old)
CH 16 – Weathering, erosion and mass wasting: interactions
between the climate and plate tectonic systems
Weathering is the general process by which rocks are broken down at earths surface. It produces all
clays and soils and are carried by streams
Chemical weathering occurs when the minerals in a rock are chemically altered or dissolved and
physical weathering occurs when a solid rock is fragmented by mechanical processes that do not
change its chemical composition. These two types do reinforce each other (the smaller the pieces the
better a chemical process has its effect on the bigger surface area)
Erosion is when particles that are produced by weathering are removed from their source
Mass wasting is when weathered and non-weathered particles move downslope in large amounts
and single events
Major factors that make weathering go at fast rate:
High solubility
Fractured rock
High rainfall
Hot temperatures
Thick soil layer
High organic content
Long exposure
Feldspar:
, Can be chemically altered to become clay minerals
It is the most abundant mineral in earths crust
It is one of the components of granite
Granite is made up from different minerals which decay at different levels of speed
The clay formed from feldspar is called kaolinite (because of the hydrolysis weathering)
The surface area is increasing when the size is decreasing
CO2 is used for weathering of calcium-rich rocks, weathering slows down when there is less CO2 in
the atmosphere, making the concentrations rise again, holding it in balance
Water breaks down granite at a very slow rate, however when an acid is added, it speeds up the
process a lot. Therefore when CO2 is desolved in H2O H2CO3 carbonic acid (sour rain)
Weathering on silicates:
Leaching ( dissolves cations and silicas)
Hydrates ( adds water to minerals)
Making solution less acidic
Reduced rate of weathering increase of CO2 climate warming, which increase weathering
reduces CO2 climate cooling reduce weathering …
Feldspar weathers continuous in moist soil and there is more acid in soil because of bacterial activity.
These two characteristics of soil make it have a higher weathering rate for rocks
There is more physical weathering in cold temperatures
Physical weathering:
Organisms (bacteria and algae, but also roots of plats and animals)
Frost
Exfoliation (flat or curved sheets break off)
More erosion when:
Longer duration
Rainfall
Increase slope steepness
Soil are layers of material created by fragmentation of rock during weathering, that experience
addition of new materials, losing of original materials and modification due through physical mixing
and chemical reactions.
Humus is organic matter and an important component of soil (decomposed plants and other
organisms)
Water can selectively remove some materials as it percolates down through the soil after rainfall in a
process called leaching (can also go the other way around when water is evaporating through the
soil)
5 factors important for formation and development of soils:
1. Parent material
, 2. Climate
3. Topography
4. Organisms
5. Time
Soil profiles:
O-horizon (loose leaves)
A-horizon (dark, highest concentration of humus)
E- Horizon (clay, insoluble minerals
B-horizon (accumulation of minerals and iron oxides)
C-horizon (slightly altered bedrock)
R-horizon (bedrock)
Downslope movements of masses of soil, rock, mud under the force of gravity, collectively known as
mass movements
Mass wasting is promoted by:
The nature of the slope materials
The amount of water in the materials
The steepness of the slope
Slopes of unconsolidated materials are the least stable of all
Water binds the particles with surface tension, however to much can separate the particles
Unconsolidated mixtures are loose in comparison to consolidated materials
Heavy rainfall or an earthquake can initiate a mass movement if the conditions are right
Three characteristics of mass movements (classification):
1. The nature of the moving material
2. The velocity of the movement (cm to km / year)
3. Sliding or flowing
Rockfall has the most velocity and has the shortest travel distance
Rockslides are slower than rockfalls
Rock avalanches differ from rockslides because their much greater velocities and travel distances,
the rocks are breaking into smaller parts when going down the slope (one of the most destructive)
Most mass movements of unconsolidated materials are slower than most rock movements
The slowest type of unconsolidated mass movement is creep (1-10mm/y)
Solifluction is the movement of soil downhill when frozen soil thaws to become more fluid
Earthflow and debris flow are faster than creep and are saturated with water
Mudflows are flowing masses made up mostly of material finer than sand and has a high water
content
Lahars is a mudflow caused by the erupted stone of a volcano that gets different properties when it
takes up a lot of water
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