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geology 1330 test 3


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Earth is composed up of several layers based on
composition and physical properties
Compositional Layers:



compositional layers



Physical Property Layers



Outer Core

Inner Core

(sphere of rock, rigid) - 100-250 km thick
- includes crust + the uppermost solid mantle
weak sphere) located in the upper
mantle - weak due to high temperatures

(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

Mohorovicic Discontinuity (Moho)
Discovered in 1909 by Andriaja
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
Spinel at ~440 km
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

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
Heat transfer by atomic or
molecular impact.
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

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

sequence of unconsolidated
consisting of pillow lavas
numerous interconnected
dikes called sheet dikes
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 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
The processes responsible for building mountains
Individual mountain building events are called an
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
-Volcanic Island Arc
-Andean-Type Plate Boundary

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
The zone where two continents collide. Often marked by pieces of ophiolite
Deformation processes at Continental Collision zones
-Crustal shortening and thickening
-Continental Escape (or Lateral Extrusion)

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
The Hydrologic Cycle
the continuous movement of H¬2O from one reservoir to another
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

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

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
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)

a plot of the discharge (or stage) at a gaging station over time
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
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)
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
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
a chemical process in which the solid is completely dissolved into ions by an acid
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.
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.
the amount of time greatly influences the character of soils
biological activity
the amount of organic activity affects soil fertility
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
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
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
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
fault creep
slow gradual displacement
faults stay locked storing up elastic energy, then suddenly slip releasing stored energy. produces large earthquakes
Device used to record and measure seismic waves generated by earthquakes
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
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
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
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
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.
unweathered parent material
detrial sedimentary rocks
formed from sediment transported as solid particles.
chemical sedimentary rocks
formed from sediment that was once in solution
chemical, physical, and biological changes that take place after sediments are deposited
changing less stable minerals to more stable minerals
precipitation occurs in 2 ways
organic and inorganic
inorganic limestone
crystalline limestone and travertine
inorgaanic limestonw. fine grained calcium carbonate precipitation from groundwater. (usually in caves)
organic limestone
the only rock made up of organic material rather than minerals
sequence of precipitation from seawater:
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
lacustrine. formed at the bottom or along the shore of lakes, as geological strata.
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
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

metamorphic foliation
the parallel alignmentof recrystallized minerals
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
bearing of a line defined by the intersection of the plane in question and horizontal
The acute angle between the plane and horizontal, measured perpendicular to strike.
(arc) older rocks on the inside
(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
the inner core is
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

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

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