geology 1330 test 3
Terms
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- Earth is composed up of several layers based on
- composition and physical properties
- Compositional Layers:
-
Crust
Mantle
Core
- compositional layers
-
Crust
Mantle
Core
- Physical Property Layers
-
Lithosphere
Asthenosphere
Mesosphere
Outer Core
Inner Core
- lithosphere
-
(sphere of rock, rigid) - 100-250 km thick
- includes crust + the uppermost solid mantle - Asthenosphere
-
weak sphere) located in the upper
mantle - weak due to high temperatures -
Mesosphere
(Lower Mantle)
-
Strong - located in lower mantle - more rigid
because increase in pressure - Outer Core
- Liquid Iron and Nickel
- Inner Core
- Solid Iron and Nickel
- Our understanding of the interior composition and structure of the earth is based on how seismic waves are
- transmitted, or propagate, through the earth
-
Significant characteristics of seismic waves include:
-
1) P waves can travel through solids and liquids.
2) S waves can travel through solids only.
3) P waves always travel faster than S waves The
velocity of seismic waves depends on the
density and elasticity of the material.
4) The velocity of seismic waves generally
increases with depth for a given layer.
5) When seismic waves pass from one material to
another they are refracted (bent) as well as
reflected - Mohorovicic Discontinuity (Moho)
-
Discovered in 1909 by Andriaja
Mohorovicic - OSERVATION OF Mohorovicic discontinuity
-
Average velocity of P waves increases
~200 km from earthquake source - Seismic Refraction
- the bending of waves as their velocity changes
- Velocity Changes in the Mantle are due to
- phase changes related to increases in pressure
- Olivine
- Spinel at ~440 km
- Spinel
- Perovskite at ~660 km
- Heat is transported in the earth by two mechanisms
- Conduction and Convection
- Convection in the outer
- core is what creates the earths magnetic field
- Continental Margins
- Passive Continental Margin and Active Continental Margin
- Passive Continental Margin
- Not tectonically active regions. Thick broad wedges of material accumulate on the margin of the Continental crust
- Active Continental Margin
- Continental margin that is tectonically active. Characterized by narrow margin of highly deformed sediments.
- Mid-Oceanic Ridges
-
Broad region of uplifted oceanic crust centered around seafloor spreading centers.
-
Topography of mid-ocean ridges is controlled by -
sea-floor spreading rates
- Spinel to Perovskite
-
Defines boundary between
Asthenosphere and Mesosphere - Earth’ internal heat engine
-
Earth’s temperature gradually
increases with an increase in depth
at a rate known as the geothermal
gradient - Sources of Earth’s internal heat:
-
-Heat emitted by radioactive decay of
isotopes of uranium (U), thorium (Th), and
potassium (K)
-Heat released as iron crystallized to form
the solid inner core
-Heat released by colliding particles during
the formation of Earth - Mechanisms of Heat Transfer
- Conduction and Convection
- Conduction
-
Heat transfer by atomic or
molecular impact. - Convection
-
Heat transfer by hot (less
dense) material rising and cold (more
dense) material sinking - Oceanic Ridges
-
Broad, linear swells
along divergent plate boundaries -
Anatomy of the
oceanic ridge -
-Occupy elevated positions
-Extensive faulting and earthquakes
-High heat flow
-Numerous volcanic structures - Concept formulated in the early 1960s by Harry Hess
- sea floor spreading
-
occurs along
relatively narrow zones, called rift
zones, located at the crests of ocean
ridges) - Seafloor spreading
- Why are oceanic ridges elevated
-
Primary reason is because newly
created oceanic lithosphere is hot and
occupies more volume (is less dense)
than cooler rocks - COMPONENTS OF OCEANIC CRUST- Layer 1
-
sequence of unconsolidated
sediments - COMPONENTS OF OCEANIC CRUST- Layer 2
- consisting of pillow lavas
- COMPONENTS OF OCEANIC CRUST- Layer 3
-
numerous interconnected
dikes called sheet dikes - COMPONENTS OF OCEANIC CRUST- Layer 4
-
gabbro, in a sequence of rocks
called an ophiolite complex - Embryonic Stage
- Formation of a continental rift
- Immature Stage
-
Formation of a narrow sea
- Mature Stage
- Development of ocean
- Formation of Ocean Basin
-
-Initial stretching and faulting of continental crust
-Embryonic Stage
-Immature stage - Destruction of Ocean Basin
-
-Declining Stage
-remnant staqe
-suture stage -
Declining Stage
- Pacific Ocean
- Remnant Stage
- Mediterranean Ocean
- Suture Stage
- Ocean is closed again
- THE WILSON CYCLE
- The cycle of formation and breakup of supercontinents
- Two known previous supercontinents
- Pangea and Rodinia
- Convergent Plate Boundary
- “Destructive†plate boundaries where oceanic crust is consumed. Also plate boundaries where mountains are built during collisions between continental crust
- Orogenesis
- The processes responsible for building mountains
- Individual mountain building events are called an
- Orogeny
- Processes at subduction zones:
-
-Backarc Spreading
-Dehydration Melting - Backarc Spreading
- At some subduction zones flow in the mantle the causes extensional stresses in the overriding plate resulting in trench rollback and backarc spreading
- Dehydration Melting
- Other subduction zones are under compressional stresses resulting in folding, thrusting, and mountain building in the overriding plate
- CONVERGENCE AT SUBDUCTION ZONES
-
-Volcanic Island Arc
-Andean-Type Plate Boundary
- CONTINENTAL COLLISIONS
- Because continents are made up of more buoyant felsic material they generally cannot be subducted into the mantle. Thus, when an ocean is closed and continents are brought together they deform by shortening and thickening
- Suture
- The zone where two continents collide. Often marked by pieces of ophiolite
- Deformation processes at Continental Collision zones
-
-Crustal shortening and thickening
-Underthrusting
-Continental Escape (or Lateral Extrusion) - Terrane
- A crustal fragment with a geologic history distinct from that of adjoining crustal fragments.
- During subduction, numerous microcontinents may be accreted to continents along subduction zones. Each accretion event is an
- orogeny
- The Hydrologic Cycle
- the continuous movement of H¬2O from one reservoir to another
- Flooding
-
along a river occurs when the volume of floodwaters exceeds the
volume of the channel to contain those waters
- What determines the volume of floodwaters at a specific location?
-
-Amount of Rainfall (inches or cm.)
-Amount of Infiltration (inches or cm.)
-Area of the Drainage Basin (mi2 or km2) -
Processes involved in the hydrologic
cycle -
-Evaporation
-Precipitation
-Infiltration
-Runoff
-Transpiration - Runoff =
- rainfall – infiltration
- Drainage Basin
- the area drained by a river at a particular point
- Drainage divide
- separates two drainage basins
- Infiltration is affected by
-
-Ground Slope
-Soil Type
-Rainfall Intensity
-Soil Saturation
-Vegetation/Land Use - Infiltration
-
The portion of precipitation that
soaks into the ground - What is the volume of excess water that a 1⬝ rainfall on the Brays Bayou drainage basin produces?
-
-Infiltration (average) = 0.2 inches
-Runoff (rainfall-infiltration) = 0.8 inches - Discharge
- the rate at which water flows past a particular point (the rate of flow)
- The equation for discharge
- The rate of flow = volume / unit time
- What units is discharge expressed in?
- feet per second
-
Discharge (Q) is measured using a simplified
form of the Continuity Equation -
Q = VA
V = average flow velocity
A = cross sectional area of water (channel) - Hydrograph
- a plot of the discharge (or stage) at a gaging station over time
- Frequency
- how often an area floods
- Frequency is measured by
-
1) Recurrence Interval
2) Exceedence Probability - Recurrence Interval
-
average number of
years between events of similar or greater
magnitude R I = (N + 1)/m
- Exceedence Probability
-
The probability
(p) of an event of a particular magnitude being
equaled or exceeded any given year is
P = 1/RI - How can you reduce flooding without reducing discharge?
- lower the stage (elevation of floodwaters) by increasing velocity of the water channel.
- The Hundred Year Floodplain
-
the area flooded by a hundred
year flood - Manning’s Equation
- v=(1.5R^2/3 S^1/2)/n
- In order to reduce flooding we want to maximize V by
-
⬢ Increase Hydraulic Radius (R)
⬢ Increase Slope (S)
⬢ Decrease Sinuosity
⬢ Decrease Roughness (n) - weathering is
- the physical breakdown and chemical alteration of rock at earth's surface.
- mass wasting is
- the transfer of rock and soil down slope under the influence of gravity
- `erosion
- the physical removal of material by mobile agents such as water, wind or ice
- types of weathering
- mechanical and chemical
- mechanical weathering
- physical forces break rock into smaller pieces without altering rock's mineral composition
- types of mechanical weathering
- frost-wedging, unloading, biological activity, and thermal expansion.
- frost-wedging is
- caused by expansion of water when bit freezes in cracks in the rocks (9% expansion)
- unloading
- process called sheeting. Reduction in pressure as rocks are exposed by erosion to allow rocks to expand
- unloading can create an
- exfoliation dome
- thermal expansion
- caused due to random motion of molecules at high temps
- geology
- the scientific study of the processes events, and conesquence of the earth's past,present, and future
- why is geology important? (5)
-
-formation of earth's landscape
-exploration of earth's natural resources
-mitigating geological hazards
-understanding environmental change
-evolution of earth and other planets - Chemical weathering
- the chemical transformation of rock into one or more new compounds
- what are some geological hazards?
- volcanoes, flooding, earthquakes, tsunamis, hurricanes, landslides.
- types of chemical weathering
- dissolution, oxidation, and hydrolysis
- dissolution
- a chemical process in which the solid is completely dissolved into ions by an acid
- oxidation
- any reaction where an element loses electrons. often affects iron bearing minerals
- what is science? (2)
-
-a body of knowledge related to the study of natural phenomenon.
-application of the scientific method: process of gatheling data though obsevation, formulating hypothesis to eplain obsevations, then testing hypothesis. - hydrolysis
- a chemical process in which a H+ ion replaces other cations in a mineral.
- what is a hypothesis?
- statement designed to explain set of obesevations (the best hypothesis explains all existing obsevations.)
- rates of weathering are controlled by
- the climate, differential weathering, mineral composition
- a hypothesis has the possibility of
- being a proven wrong. (falsifiable)
- climate: the wetter and hoter the climate,
- the greater the role of chemical weathering
- climate: the colder and dryer the climate,
- the greater the role of mechanical weathering
- differential weathering
-
different lithologies weather at different rates
- how do you test a hypothesis?
- collect data and test prediction. if data inconsistent with peraiction,hypothesis is abandoned.
- parent material
- source of weathered material tat soil develop from residual soils and transported soils
- risidual soils
- soils developed from underlying bedrock
- transported soils
- developed on and from unconsolidated sediments
- what is a theory?
- a well tested and widely accpted view that scientists agree best explain certain observational facts.
- time
- the amount of time greatly influences the character of soils
- biological activity
- the amount of organic activity affects soil fertility
- topography
- soils develop poorly on steep slopes.
- continental drift
- the hypothesis that all the continents had once fit together to form a super continent and has subsequently difted apart to their present positions.
- soil profile
- soil forming processes work from the surface downward. these different layers are horizons and the verticle coss section is the soil profile
- o horizon
- mostly organic material
- evidence supporting continental dift
- geometric fit, geological matches, fossl maches, pateocimatic evidence.
- 'A' horizon
- largely organic material. lots of biological activity. still humus present
- nebular hypothesis
- the bodies of our solar system evolved from a rotating cloud of gas and dust (solar nebula)
- solar nebula starts to gravitationally collapse
- 5 billion yrs ago (5Ga)
- formation of the solar system
-
-nebula started to collapse.
-nebula contracts into rotating disk, heated by convrsion of gravitational to thermal energy (formation of protosun).
-nebula cloud cools, causing condensation of tiny rock and metallic particles.
-repeated collisions caused dust particles to coalesce into asterold-sized bodies (protoplanets).
-bodies accreted into planets with in a few million years. - absolute dating
- determining the numerical age of different rock units
- radioactivity
- the spontaneous decay of the nucleus of certain isotopes
- radioactive decay of an unstable parent isotope results in
- formation of a stable daughter isotope
- three types of radioactive decay
- Alpha particle emmisions, beta particle emmisions, and electron capture
- half-life
- the time required for one-half of the unstable parent isotope to decay to its stable daughter isotope
- alpha particle emissions
- emits protons and neutrons from the daughter nucleus
- beta particle emission
- electron emission
- radioactive decay series
- the series of intermediate radioactive daughter prdoucts that are produced during the decay of a radioactive parent isotope to its stable daughter
- geological time scale
- divisions in the stratigraphic column based on variations in preserved fossils.
- the geological time scale is built by
- using a combination of stratigraphic relationships, cross-cutting relationships, and absolute ages.
-
How can isotopic dating of igneous rocks tell us anything about the age
of sedimentary rocks and the fossils they contain? - super position and cross cutting relationships
- earthquake
- the vibration of the earth in response to a rapid release of energy
- Large earthquakes are associated with the buildup and release of elastic strain during movement on
- faults
- fault creep
- slow gradual displacement
- stick-slip
- faults stay locked storing up elastic energy, then suddenly slip releasing stored energy. produces large earthquakes
- Seismometer
- Device used to record and measure seismic waves generated by earthquakes
- seismographs
- instruments that record seismic waves
- body waves
- travel through earths interior. (primary 'p' waves, secondary 's' waves)
- P waves
- Push-pull waves, like sound waves
- S waves
- shaking waves
- triangulation
- the method by which scientists locate the epicenter
- how many seismographs do you need to locate the epicenter?
- 3. The station where all three station reading intersect is the epicenter
- intensity of an earthquake is based on
- the amount of damage
- magnitude
- measures the amount of energy released during an earthquake
- Richter Scale
- determines eq magnitude from deflections on seismographs
- relative dating
- determining the sequence of formation of different rock units
- law of superposition
- the older rocks are on the bottom and the younger are on the top. "principle of the messy desk"
- principle of cross-cutting relationships
- younger features cut across older features
- significance of inclusion
- if a fragment of one rock is included within another rock, the inclusion is the older of the 2 rocks
- unconformity
- a buried surface of erosion. represents a period of missinbg time within the geological record when deposition ceased.
- unconformity: disconformities
- unconformities where the beds below the ersional surface are parallel to the beds above the ersional surface
- unconformity: Angular unconformities
- unconformity where the beds below the erosional surface are at an angle to the beds above the erosional surface
- unconformity: nonconformity
- an unconformity where the buried erosional surface is developed on exposed plutonic or metamorhic rocks.
- matching rocks of similar age from one region to another is
- Correlation of rock layers
- fossils
- te remains or traces of prehistoric life
- index fossils
- fossils that can be used to narrowly constrain the age of a sedimentary rock
- what 2 conditions are generally necessary for a fossil to be preserved in the geologic record?
- posession of hard parts and rapid burial
- characteristics of a good index fossil
- widespread, rapidly involving, easily recognizable
- E horizon
- mostly mineral material.
- E horizon: eluviation
- As water percolates through the soil, smaller particles are washed away by leaching
- E horizon: leaching
- Water dissolves soluble material carrying it downward and depleting the horizon.
- B horizon
- subsoil. most material removed from the Ehorizon is deposited in the B horizon.
- O,A,E,B horizons are the
- Solum (true soil)
- C horizon
- partially altered parent material. not considered true soil.
- bedrock
- unweathered parent material
- detrial sedimentary rocks
- formed from sediment transported as solid particles.
- chemical sedimentary rocks
- formed from sediment that was once in solution
- diagenesis
- chemical, physical, and biological changes that take place after sediments are deposited
- recrystallization
- changing less stable minerals to more stable minerals
- precipitation occurs in 2 ways
- organic and inorganic
- inorganic limestone
- crystalline limestone and travertine
- travertine
- inorgaanic limestonw. fine grained calcium carbonate precipitation from groundwater. (usually in caves)
- organic limestone
- Coquina,
- coal
- the only rock made up of organic material rather than minerals
- sequence of precipitation from seawater:
-
1-calcite
2-gypsum - cross-bedding
- nonhorizontal layering within individual beds
- beds (strata)
- layers of sediment that have accumulated in a depositional environment
- graded bedding
- particle size changes within a single sedimentary bed from coarse at the bottom to fine at the top
- ripple marks
- small waves of sand that develop on the surface of beds due to moving water or air
- alluvial fan
- a fan shaped alluvial deposit formed by a stream where its velocity abruptly decreased
- lake
- lacustrine. formed at the bottom or along the shore of lakes, as geological strata.
- eolian
- wind. noting or pertaining to sand or rock material carried or arranged by the wind
- sedimentary facies
- a portion of rock unit that has a distinct set of characteristics that distinguishes it from other parts of the same unit
- metamorphism
- the solid-state change in composition and/or texture of a rock due to high temperatures, pressures or fluids in the earth.
- agents of metamorphism
-
-heat
-stress/pressure
-fluids - metamorphic foliation
- the parallel alignmentof recrystallized minerals
- shear
- oppositely directed forces acting parallel to one another across a surface
- tensional stress
- differential stress that elongates a rock body
- compressional stress
- differential stress that shortens a rock body
- 3 types of strain
- elastic, ductile, brittle
- elastic deformation
- a temporary change in shape that recovers
- ductile deformation
- a permanent change in shape and size that is not recovered when the stress is removed
- brittle deformation
- the loss of cohesion of a body under the influence of applied stress. (it breaks)
- Factors Determining the Style of Deformation: Pressure
-
-high P= ductile deformation
-low P= brittle deformation - Factors Determining the Style of Deformation:
-
-high temp= ductile deformation
-low temp= brittle deformation - Factors Determining the Style of Deformation: strain rate
-
-high SR= brittle deformation
-low SR= ductile deformation - Factors Determining the Style of Deformation: Rock Composition
- -Hard= brittle deformation
- strike
- bearing of a line defined by the intersection of the plane in question and horizontal
- dip
- The acute angle between the plane and horizontal, measured perpendicular to strike.
- anticline
- (arc) older rocks on the inside
- syncline
- (trough) younger rocks on the inside
- plunging fold
- where the hinge line is not horizontal
- recumbent fold
- the axial plane of a fold is horizontal
- overturned hold
- one limb of the fold is tilted beyond vertical
- Asymmetric fold
- the limbs of a fold are not the same length
- hinge line
- the line formed by the intersection of the axial plane and a bedding plane
- axial plane
- the plane of mirror symmetry dividing the fold into two planes
- normal faults
- a dip-slip fault where the hanging wall moved down relative to the footwall
- reverse fault
- a dip-slip fault where the hanging wall moved up relative to the foot wall
- as earth formed temperatures increased due to
- collisions, compression, and radioactivity
- increased temperatures result in melting of components of earth causing
- chemical differentiation
- during chemical differentiation metals: (iron, nickel)
- sink toward center of earth
- during chemical direction differentiation, rocky material: (sodium, calcium, Al)
- rise toward surface of earth
- composition layers
- crust, mantle, core
- the crust is divided into 2 components
- oceanic and continental crust
- outter core is
- fluid
- the inner core is
- solid
- Rock cycle
- the geological processes that act to transform one rock type into another
- 3 major types of rock
- igneous, metamorphic, sedimentary
- igneous to sedimentary
- igneous rock goes through weathering, transportation and deposition. once turned to sediment, it goes through cementation and compaction (lithification)
- sedimentary rock to metamorphic
- heat and pressure occurs (metamorphism)
- metamorphic to igneous rock
- melting occurs. one turned to magma, it goes through cooling and solidification
- igneous rocks
- rocks formed from the crystallization of magma. (intrusive & extrusive)
- sedimentary rock
- rocks formed at the surface of the earth, derived from preexisting rock. (detrial & chemical)
- detrial sedimentary rock
- formed from the deposition of solid particles. i.e. sand
- chemical sedimentary rock
- formed from the precipitation of dissolved material (i.e. carbonate)
- metamorphic rocks
- rock formed from the solid state alteration of preexisting rocks due to increased temp or pressure or chemically active fluids
- principles of uniformitarianism
- the processes that have shaped the earth in the past are essentially the same as those operating today
- Alfred Wegener is considered
- father of continental drift
- What most likely caused the continents to drift apart?
- seafloor spreading, plate tectonics
- Henry Hess is considered
- father of seafloor spreading
- Henry Hess' seafloor spreading hypothesis
-
1) sea floor formed at mid-ocean ridges
2) sea floor consumed at trenches
3) process driven by convection in the mantle - paleomagnetism
- the study of earth's past magnetic field as preserved by magnetic minerals in rocks.
- what were the 2 important discoveries from paleomagnetism that supported plate tectonics and seafloor spreading?
-
1)change in magnetic inclination with latitude
2)magnetic reversals - plate tectonics
-
-a model explaining how earth works.
-the collection of ideas that explain the observed motion of earth's outer shell through the mechanisms of subduction and seafloor spreading, which generate earth's major features; continents, mountains, &ocean basins. - 7 major plates that m ake up the surface of the earth
- north america, south america, eurasia, africa, australian-indian