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What is Relative Dating?
Using the relationships between rock units, it is possible to assign relative times to what we see in nature. Relative dating is where one set of rocks is compared to another to determine which is older or younger.
Who is credited with starting modern geology through publication of Theory of the Earth?
What is the Principle of Uniformitarianism?
"The key to the present is the past"-processes that act today, acted the same way in teh past.
Who is Nicolas Steno?
He is credited with being the first person to recognize geologic history through rock relationships.
What three ideas did Nicolas Steno develop?
1. Original Horizontality: All sedimentary sequences form as flat, horizontal beds. Aby tilting or folding must occur AFTER the rock is formed.
2: Superposition: The oldest rocks are always on the bottom and the youngest are on teh top.
3. Lateral Continuity: Sedimentary deposits will extend out laterally in all directions. Eventually they will thin out or be terminated by the edge of a basin.
What is the principle of Cross-Cutting Relationships
Any structure that cuts another must be younger that what it cuts.
An unconformity is where part of the rock record is missing.
This type occurs between two parallel rock beds, both sedimentary
This type is also between two sedimentary rock beds, but in this case, both rock units are NOT parallel. The upper units will be horizontal and the lower units will be tilted.
This type occurs between two DIFFERENT types of rock. Non=Not the same.
What is the Principle of Inclusions?
This applies to any rock unit containing pieces of another rock. The rock unit is younger than the pieces.
What is the principle of Fossil Succession?
Best fossils for dating are Index Guide fossils. These are fossils of organisms that are known to have existed for only limited time periods.
What is Half-Life?
Decay occuring at a specific rate. This is the time it takes for half of the radioactive parent atoms to be converted into stable daughter atoms.
What are the three types of radioactive decay?
1. Alpha Decay: The isotope will lose 2 protons anad 2 neutrons. As a result, the atomic number will change by 2 and the atomic mass (protons plus neutrons) will change by 4.
2. Beta Decay: The isotope will lose 1 electron. This electron is given off by a neutron, which causes it to change into a protron. Resulting in a positive change of one to the atomic numner, but no change in mass.
3. Electron Capture: This is the opposite of beta decay. Isotope gains an electron, converting a protron to a neutron. Resulting in a negative change of one to the atomic numner and no change to the atomic mass.
What kind of system does decay reqire in order to happen?
Closed System. This means that niether the parent nor the daughter atoms can escape.
What are the Geologic Time units?
What is the largest block of time of all?
PreCambrian. It accoutns for 87% of all geologic time.
When rocks are changed from their original shape or relationship, they have been deformed.
What causes Deformation?
It is caused by stress.
Stress is a FORCE applied to a rock.
What is the result of stress?
Strain. This is the changing of the rock,
What are the different types of stress?
1. Compression: This type of stress pushes the rocks together. Causes shortening and thickening of the rock.
2. Tension: This type pulls the rocks apart. Causes lengthening and thinning of the rock.
3. Shear: Two opposing forces act parallel to one another to displace rock. The rock just pushes past each other, with no change in shape.
Describe Elastic deformation/strain
Once the stress is removed, the rock returns to its original shape with no changes.
Describe Plastic deformation/strain
The rock is BENT permanently. This type is found deep in the Earth, where temperatures are high. The result is Folds.
Describe Brittle deformation/strain
The rock is BROKEN permanently. This type is foound at shallow depths, near the surface, where temps are low. The result is Faults and Fractures.
What is Strike?
This is the compass direction of the intersection of a bed with the horizontal plane defined by the Earths surface. It is always measured from NORTH.
What is Dip?
This is the angle between the horizontal and the top of an inclined bed. It is always measured perpendicular to strike.
All folds consist of two lembs and an axis plane. Fold is bending. There are different types depending on how the rocks are bending.
What is an Anticline?
This is a hill shaped (sad face), upward-bowing fold. The limbs are being bent down in respect to the axial plane. THE OLDER UNITS WILL BE AT THE CENTER OF THE FOLD.
What is a Syncline?
This is a basin/bowl shaped, downward-bowing fold. The limbs are being bent up in respect to the axial plane. THE YOUNGER UNITS WILL BE IN THE CENTER OF THE FOLD.
How do Anticlines and Synclines commonly occur?
Describe how axial planes tilt.
If tilted away from vertically, this can create over-turned or asymetrical folds.
If tilted away from horizontally, this can create a plunging fold.
What are Domes?
Domes occur through upwarping of the underlying rock.Caused also by intrustions like laccoliths.
What are Basins?
Thought of as a double syncline and show the same characteristics: youongest rocks will be in the center and the dips will point in towards the center.
What is a Monocline?
This is a fold that is only a small bend or flexure int he rocks. It essentially is only half a fold (mono=one).
Describe a Joint?
Fractures in the rock with no associated motion. They are caused by cooling and pressure release and also horizontal and vertical pressure on teh rocks.
Descibe a Fault
Fractures in the rock WITH motion.
What is a Dip-slip fault
Motion in these faults is UP and DOWN
What is a normal fault?
Faults caused by tensional stress-the rocks are being PULLED apart.
What is a Reverse Fault?
Faults caused by compressional stress-the rocks are being PUSHED together. The hangingwall goes UP relative to the footwall.
What is a Strike-Slip fault?
Motion in faults is BACK and FORTH.
What is an Oblique-Slip Fault
Combination of Dip-Slip and Strike-Slip. Visible of motion is viewable on both the map view and cross-section views.
Earthquakes occuring when energy in rocks is released.
How is energy released in an earthquake?
Through Seismic waves
What are the types of Seismic waves?
P-waves: Theses are PRIMARY waves and occur first in a PUSH-PULL motion.
S-waves: These are SECONDARY waves, they happen second in a UP_DOWN motion. They cannot travel through liquid.
How is the actual location of an Earthquake given?
1. Focus: This is the actual position where the quake occured. It is located below the ground and the seismic energy dissipates from this point in all directions.
2. Epicenter: This is the point on the surface directly above the focus. This is the position given in media reports.
How is intensity and magnitude measured of an earthquake?
1. Modified Mercalli Scale: This is based on intensity and damage. This scale is purely visual, with no instruments needed.
2. Richter Scale: Based on magnitude, the actual energy released during the earthquake. Determined by the difference in arrival times of the P wave and S wave and the size of the waves recoreded on the seimogram. There is not a steady progression in size from one number to the next.
Where do earthquakes typically occur?
Very close to p[late boundaries.
What is Liquefaction?
Occurs in unconsolidated, wet sediments. During a quake, dry sediments will shake into a more tightly consolidated arrangement.
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