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Geology Test 2 Review


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Uniformiterianism (Actualism)
"the same natural laws that exist today and govern the earth has governed the earth forever.
Types of dating
Relative & Absolute
Relative Dating
Original Horizontality, Superposition, Lateral Continuity, Cross cutting relationships
Original Horizontality principle
when beds are forming they are originally deposited horizontally
Superposition principle
older rocks on the bottom, younger rocks on top
Lateral continuity principle
normally bed extends laterally until in pinches out to nothing ex. Mt St Helens ash. If it ends in a blunt/cut off end then something must have happened to it.
Cross cutting relationships principle
a geological feature that cuts across rock is younger that the rock it cuts across – a dike is younger than the layers that it cuts across – the fault is younger than the rock it cut through
Inclusions principle
fragments that are included in the host rock are older than the host rock - ex. Xenoliths
"a surface where there is a gap in the geologic record “Time is missing”
Angular unconformities
"beds below the unconformity are not parallel to the beds above the
Non Conformity
sediments are deposited on intrusive igneous or metamorphic rocks
rock layers above & below the unconformity are all parallel. – one way to tell if time is missing – if one layer that has fossils is next to a layer that also has fossils of different time period.
determining the time equivalency of rock units using Physical continuity, Rock types, Fossils
Absolute dating
Isotopic and Radioactive decay
Isotopic Dating
Parent, Daughter, half life
Radioactive Decay
Alpha Decay, Beta Decay, electron capture
Geological Structure
Stress & Strain
force acting on a rock
change in shape and or size of a rock as a result of stress
Types of Stress
Compression, tensional stress, shear
Types of deformation
Elastic, Ductile, Brittle Deformation
Compression Stress
pushing together - stress results in shortening strain
Tensional Stress
pulling apart – results in extensional (lengthening) strain
Shear force Stress
parallel forces pushing in opposite direction
Elastic deformation
Rocks return to their original shape or dimension after stress is released
Ductile deformation
fold or bend – rocks that are like playdough – it will not go back to its original shape
Brittle Deformation
breaks rocks
bend in rock units – results from ductile deformation
Types of folds
Anticline, Syncline, Plunging, Structural dome, Structural basin
Anticline fold
Upward arching fold
Syncline fold
trough shaped – downward arching
Plunging fold
axis is not horizontal
Structural dome fold
all beds dip away from a central point
Structural basin fold
all beds are toward a central point (salad bowl)
Shapes of folds
Open Folds, Isoclinal folds, Overturned folds, Recumbent folds
Open folds
less intense stress
Isoclinal folds
intense stress – ie: Christmas ribbon candy
Overturned Fold
shear stress or unequal compressive stress
Recumbent Fold
formed in the center of mountain ranges where there is a lot of crustal shortening (Himalayas)
Parts of a fold
Limbs, Axis, Axial plane
Break in a rock, result of brittle deformation
Kinds of fractures
Joint, Fault
Parts of a fault
Fault Plane, Fault Trace, Hanging wall, Foot wall
Best places to observe faults
Roadcut, quarries, sea cliffs
Types of faults
Dip Slip Fault, Strike Slip Fault
Types of Dip Slip Faults
Normal, Reverse, Thrust
Earthquakes occur when
the stress exceeds rupture strength of rock, Stress exceed friction between the rocks on opposite sides of fault, mass changes
Parts of an Earthquake
Focus, Epicenter, fault trace
Point on a fault where the first movements take place
Point on earth's surface directly above the fault
Study of Earthquake waves
Types of earthquake waves
Body waves - p & s waves Surface waves - Raleigh & love waves
P Wave
Compressional waves - push pull movement - travels through solids & liquids
S Wave
Shear waves - side to side motion - only travels through solids
Raleigh waves
Surface wave - up & down movement - like being on a ship - SS Raleigh
Love waves
Surface wave - side to side movement - causes the most damage
Instrument used to measure earthquake waves - has to be anchored in bedrock
An object at rest tends to stay at rest
Which wave is faster
P wave is faster that S wave
Equation determine distance earthquake
Number of recording Seismograph
Need minimum of 3 recording seismographs to determine epicenter of earthquake
Measuring wave
Can only measure distance not direction of waves
Earthquake Size
Intensity & Magnitude
Intensity of Earthquake
What you feel
Magnitude of Earthquake
measure of total energy released in a earthquake
How do you measure Magnitude
Richter Scale, Moment Magnitude
Earthquake Damage
Ground shaking, Tsunami, Liquification, Landslides
Predicting Earthquakes
Microseisms, Water well levels, animal behavior, Paleoseismology
Way to tell what’s under surface of earth
Earthquake waves, Volcanoes Kinder light, Physics Laws
Classical Layers of earth defined by
defined by the composition of layers
Classical Layers of earth
Crust, Mantle, Core
Oceanic Crust
thin, dense, Rock - Mafic, basalt/gabbro, Minerals – amphiboles, plagioclase, olivenes, pyroxene
Continental Crust
thick, Less dense than oceanic crust, Rock – Felsic, grantite/rhyolite, Minerals – quartz, k Spar, micas
denser, Rock – ultramafic, peridotite, Minerals – olivine – pyroxene, garnet
Very dense, mostly iron (Fe) – a little O, S, Si
boundary between crust & mantle where seismic waves speed up.
Ultra Low Velocity Zone – Seismic waves slow down
Geophysical Layers - defined by
Defined by the state that the matter is in
Geophysical Layers
Lithosphere, Asthenosphere, Mesophere,Outer Core, Inner Core
Crust and the upper mantle, Solid
Extends from the base of the lithosphere to depth of 660 km, Plastic – flows very slowly
Solid – due to pressure
Outer Core
Liquid - because it is liquid we have a magnetic field
Inner Core
Solid – because of pressure
Balance of equilibrium of blocks of crust, the crust is very thick under mountains, Crust will rebound with pressure off
Magnetic Field
Region of magnetic force that surrounds the earth, Generated by convection currents in the outer core, Polar reversals
Study of ancient magnetic fields, Curie Point - magnets lose magnetism - 580, When cooled - magnet points in direction of pole

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