Term
| What question does relative dating ask? |
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Definition
| In what order did geological events happen? |
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Term
| What are the principles of relative age dating? |
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Definition
Superposition
Original Horizontality
Cross-cutting relationships
Inclusions
Unconformities
Angular unconformity
Disconformity
Nonconformity |
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Term
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Definition
• Developed by Nicolaus Steno in 1669
• In an undeformed sequence of sedimentary rocks the oldest rocks are on the bottom |
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Term
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Definition
• Layers of sediment are generally deposited in a horizontal position
• Rock layers that are flat have not been disturbed |
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Term
| Cross cutting relationships |
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Definition
| • Younger features cut across older feature |
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Term
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Definition
• An inclusion is a piece of rock within another rock
• Rock containing the inclusion is younger |
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Term
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Definition
| • An unconformity is a break in the rock record produced by erosion and/or non-deposition of rock units |
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Term
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Definition
| • Tilted rocks are overlain by flat-lying rocks |
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Term
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Definition
| • Strata on either side of the unconformity are parallel |
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Term
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Definition
| • Metamorphic or igneous rocks in contact with sedimentary strata |
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Term
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Definition
| Traces or remains of prehistoric life now preserved in rock |
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Term
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Definition
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Term
| What rocks are fossils found in? |
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Definition
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Term
| What do fossils aid in the interpretation of? |
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Definition
| geologic, geographic, and environmental past |
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Term
| Conditions favoring preservation |
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Definition
• Rapid burial
• Possession of hard parts (skeleton, shell, etc.) |
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Term
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Definition
• Fossil organisms succeed one another in a definite and determinable order
• Most any time period can be recognized by its fossil content
• Matching of rocks of similar ages in different regions is known as correlation
• Correlation often relies upon fossils |
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Term
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Definition
• Unstable isotopes emit particles and energy in a process known as radioactive decay
• Radioactive decay occurs at known rates and using this you can determine the age of certain types of rocks. |
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Term
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Definition
| unstable radioactive isotope |
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Term
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Definition
| results from the decay of a parent |
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Term
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Definition
| the time required for one-half (50%) of the parent to change to daughter product |
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Term
| What tells us the age of the sample? |
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Definition
| Comparing the ratio of parent to daughter |
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Term
| Sources of error in radiometric age dating |
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Definition
• No parent or daughter is added or subtracted
• No daughter product at start
• Decay is consistent with time |
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Term
| How do you avoid error in radiometric dating? |
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Definition
| only fresh, unweathered rock samples should be used |
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Term
| Sources of error in detrital and metamorphic rocks |
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Definition
• Detrital sedimentary rocks are not the same age as the rock in which they formed
• Metamorphic rock age may not necessarily represent the time when the rock formed |
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Term
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Definition
a) Precambrian time
b) Phanerozoic |
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Term
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Definition
• Eon: the greatest amount of time
• Era
• Period
• Epoch: smallest amount of time |
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Term
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Definition
• Almost 4 billion years of time prior to the Phanerozoic
Comprised of
• Proterozoic Eon: 540 to 2500 MYA
• Archean Eon: 2500 to 3800 MYA
• Hadean Eon: 3800 to 4500 MYA |
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Term
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Definition
• “Visible life”
• Most of earth’s history is preserved here.
Comprised of
• Paleozoic Era: 570 to 245 MYA
• Mesozoic Era 245 to 66 MYA
• Cenozoic Era: 66 MYA to present |
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Term
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Definition
570 to 245 MYA
• Dominant large animals: Amphibians/fish
• Continents mostly together, similar animals and plant species, flat-few mountain ranges, large, warm, clear, shallow seas.
• Appalachians form 350 to 400 MYA. |
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Term
| Periods in the Palezoic era |
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Definition
• Cambrian (oldest),
• Ordovician,
• Silurian,
• Devonian,
• Mississippi,
• Pennsylvanian,
• Permian (youngest) |
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Term
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Definition
245 to 66 MYA
• Dominant large animals: Reptiles/dinosaurs
• The continents began pulling apart,
• More diversity in plant and animal species.
• Increased mountain building and with that, lots of sediment from erosion.
• Pangaea begins to breakup at about 200 MYA.
• Rocky Mountains form 66 to 120 MYA. |
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Term
| Periods in the Mezzezoic era |
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Definition
• Triassic,
• Jurassic,
• Cretaceous |
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Term
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Definition
66 MYA to present
• Dominant large animals: Mammals
• Mountain building begins to slow
• Lots of erosion of existing mountains.
• Himalayas form 45 MYA. |
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Term
| Quantenary Period composed of two Epochs |
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Definition
• Pleistocene (oldest),
• Recent (less than 10,000 years) |
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Term
| Crustal deformation happens through |
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Definition
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Term
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Definition
the force applied to rocks
• Compressional stress: shortening of a rock body
• Tensional stress: stretching of a rock body
• Shear: tearing and twisting of a rock body |
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Term
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Definition
the response of a rock to stress, deformation
• Generally involves a change in shape of the rock |
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Term
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Definition
Elastic deformation
Ductile/Plastic deformation
Brittle deformation |
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Term
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Definition
• Changes in shape of rock are reversible (deform it, remove the stress and it returns to its original shape
Ex: a rubber band, San Andreas fault |
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Term
| Ductile/Plastic deformation |
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Definition
• Changes in shape of rock are permanent and not reversible (like folding)
Ex: Silly putty pulled slowly or warm taffy |
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Term
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Definition
• Rocks break once the elastic limit is surpassed
• They will fracture (rupture) if the rock is brittle
Ex: Silly putty pulled quickly or a dry stick |
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Term
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Definition
• Measurements used to find the orientation of a rock unit or fault surface
• Important tool for geologic maps |
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Term
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Definition
| • Compass direction, level/horizontal direction on the bedding or fault plane |
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Term
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Definition
• Angle of inclination, max. angle perpendicular to strike.
Ex: Follows natural flow direction of water on surface |
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Term
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Definition
Axial plane
Axis
Limb
Limb dip angle
Plunging
Double Plunging |
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Term
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Definition
i) Anticline
ii) Syncline
iii) Monocline
iv) Domes and basins |
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Term
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Definition
• Uplifted strata in which layers slope away from the axis of the fold or central ridge
• When eroded, oldest rocks are in middle and dip away from axis |
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Term
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Definition
A trough in folded strata with beds that slope toward the axis of the downfold
• When eroded youngest rocks are in middle and dip toward axis |
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Term
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Definition
| Step-like folds in horizontally sedimentary strata |
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Term
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Definition
• Dome: upwarped, circular fold, dip away from center
• Basin: downwarped, circular fold, dip toward center |
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Term
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Definition
| A faulting displaces or offsets normally continuous features: a bedding plane, a road, a stream. |
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Term
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Definition
Normal fault
Thrust (low angle) or reverse fault (high angle)
Strike slip fault |
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Term
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Definition
• Tensional setting
• Hanging wall is pulled below the footwall |
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Term
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Definition
• Compressional setting
• Hanging wall is pushed above the footwall |
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Term
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Definition
• Horizontal movement along a fault-line.
• Right lateral vs. left lateral (relative motion) |
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Term
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Definition
• Fractures across which no displacement or offset has occurred.
• Columnar joints are a very special (6-sided) type of joint system found typically in basaltic lava flows |
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Term
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Definition
• An Earthquake is a sudden movement of the Earth’s crust, which originates at or below the surface
• Invaluable for studying the interior of the Earth |
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Term
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Definition
• Tectonic activity
• Volcanic eruptions
• Bomb testing |
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Term
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Definition
| Small earthquakes that can precede a major earthquake. |
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Term
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Definition
| Smaller earthquakes that follow the main earthquake. Very common |
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Term
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Definition
| An instrument that records earthquakes |
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Term
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Definition
| The zone within the Earth (at depth) where rock displacement produces an earthquake |
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Term
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Definition
| On the Earth’s surface, directly above the focus of an earthquake |
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Term
| Properties of seismic waves |
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Definition
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Term
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Definition
• Move through the material by compressing it
• Highest velocity of all seismic waves
• Reaches seismographs first |
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Term
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Definition
• Velocity is less than P waves
• Does not travel through liquids |
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Term
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Definition
• Travel along surface of the Earth
• Behave like S waves
• Causes intense ground motion during an earthquake
• Slower than P or S waves |
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Term
| Locating epicenter on an earthquake |
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Definition
• Location found by using a series of seismographs
• Determination of elapsed time between arrival of first P wave and first S wave
• Use a time-distance graph to determine distance to the epicenter from seismic station
• Triangulate using 3 or more stations to get location |
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Term
| How do do you measure an earthquake? |
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Definition
Modified Mercalli Intensity Scale
Richter Scale
c) Seismic moment |
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Term
| Modified Mercalli Intensity Scale |
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Definition
• Measures earthquake intensity: Subjective degree of shaking
• Depends energy released and distance to epicenter
• Type of ground material (soft, hard)
• Describes damage to structures
• Ranges from I (only felt by a few) to XII (total destruction) |
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Term
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Definition
• Measures earthquake magnitude
• Measures energy released at source of earthquake
• Use amplitude of wave taken from seismograph
• Logarithmic scale used to express magnitude. Each number on Richter Scale has 32 times more energy |
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Term
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Definition
• Used for the largest earthquakes
• Uses rock properties as well as more distant seismographs
• Near seismographs may be max’d out. |
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Term
| Earthquakes and plate tectonics |
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Definition
• Mostly near plate boundaries
• Three main plate boundaries: Divergent (smallest), Transform (medium) and Convergent (largest). |
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Term
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Definition
• Earthquakes are shallow, more frequent
• Generally low magnitudes |
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Term
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Definition
• Continental transform-medium magnitudes, thick, cool crust-San Andreas Fault Zone
• Oceanic transform- mostly near MOR, thin, plastic, warm crust-lower magnitudes |
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Term
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Definition
• Largest magnitudes
• Commonly in subduction zones
• The largest earthquakes on earth: 1960 Chile 9.4 |
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Term
| Types of earthquake destruction |
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Definition
Ground motion
Tsunami
Landslides and ground instability
Fires
Seiches |
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Term
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Definition
seismic sea waves
• Earthquakes under the ocean but on/near seafloor
• Waves travel at 400-500 mph in open ocean
• Low height in open ocean (less than 1m)
• When entering shallow water, they rapidly decelerate and build in height from momentum
• First sign can be withdrawal of water from coast; a few minutes later the crest arrives |
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Term
| Landslides and ground instability |
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Definition
• Commonly triggers landslides
• Liquefaction: stable high-fluid content soil turns fluid-like, mostly where loose fill has been added |
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Term
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Definition
| • Sloshing in lakes may cause dams to break |
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Term
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Definition
Past patterns
From trenching
Foreshocks and Ground tilt/bulge
Changes in animal behavior |
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Term
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Definition
• Originally measured by lowering lines overboard
• Sonar invented in the 1920s
• Reflects sound waves off the ocean floor |
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