NAS 145 Test 2
numerical (absolute) dating
"exact age" of rock body within error bars isotopic dating uses physics of radioactive decay
Are earthquakes related to faults/plate boundaries?
Earthquakes are sometimes caused by fault boundaries but they have different relationships depending on the boundary itself
Define 'earthquake' and how seismic waves are produced.
Earthquakes are the vibration of the earth produced by a rapid release in energy seismic waves are produced when plates build up stress along faults until the energy is released and radiates in a wave in all directions from the source of release also known as the hypocenter
What is foliation?
Foliation refers to any planar arrangement of mineral grains or structural features within a rock it's also sometimes called rock cleavage
Principle of Fossil Succession
Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.
What force prevents movement along faults?
Friction is the force that prevents movement along the folds and allows for the building of pressure.
What are two types of base levels? What force drives water to these?
Local (Lake) Ultimate Ocean
What role does velocity play in the creation and evolution of a meandering stream?
Meanders form because water increases velocity around the outside of a curve, increasing erosion at a place called a cutbank, and decreases velocity around the inside of a curve, causing deposition at a place called a point bar.Over time, meanders migrate into highly exaggerated loops.Eventually these loops are cut off as the stream finds a more efficient path, and the loop left behind becomes an oxbow lake.
Metamorphic rocks are produced from which types of rocks (sedimentary, igneous, or metamorphic)?
Metamorphic rocks can be created from sedimentary igneous and other metamorphic rocks
Relative dating
Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock
Where does hydrothermal metamorphism widely occur?
Mid ocean Ridge systems is where they most often occur where cold water seeps into rocks.
Heat
Most important agent (~200 to 850°C) Recrystallization and neo-crystallization results in stable and/or new minerals
Describe the longitudinal profile of a stream. How do gradient, channel size, channel roughness and velocity change?
Near the headwaters of the stream § Gradient is steep § Discharge is low § Competence is high (Sediment is coarse) § Channels are straight § Channels are rough § Channels are narrow § Factors are generally Opposite near the Stream's base level. o Not near the headwaters § Gradient is less steep § Discharge is High § Competence is Low (Sediment is coarse) § Channels are not straight § Channels are smooth § Channels are wide § Factors are generally Opposite near the Stream's base level.
Which waves are associated with push-pull movement?
The P waves also known as the primary waves are the ones responsible for the push pull compress and expand motion
What is a half-life and what role do parents and daughters play?
The amount of time that they take it takes for 50% of the radioactive atom to decay into daughter isotopes
What is the difference between an earthquake's epicenter and a focus (hypocenter?)
The epicenter is the point on the surface above the above the hypocenter
How does metamorphic grade relate to temperature?
The higher the temperature the higher the metamorphic grade
zone of saturation
The lower zone where water accumilates between small rock particles.
porosity
The percentage of the total volume of a rock or sediment that consists of open spaces.
how does metamorphic grade relate to degree of change?
What metamorphic grade represents the degree of change from high to low
radiocarbon dating
a chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon-14
index fossil
a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
Richter scale
a logarithmic scale of 1 to 10 used to express the energy released by an earthquake
moment magnitude
a more precise measure of earthquake magnitude than the Richter scale, which is derived from the amount of displacement that occurs along a fault zone and estimates the energy released by an earthquake
Artesian well
a situation in which groundwater under pressure rises above the level of the aquifer
Types of unconformities
angular, disconformity, nonconformity
point bar
deposit of sediment build up by a river on the inside bend of a meander
Darcy's law
if permeability remains uniform, the velocity of groundwater will increase as the slope of the water table increases
zone of aeration
upper soil layers that hold both air and water
Describe how a cone of depression may develop
when groundwater is pumped from a well. In an unconfined aquifer (water table), this is an actual depression of the water levels. In confined aquifers (artesian), the cone of depression is a reduction in the pressure head surrounding the pumped well.
Principle of Cross-cutting Relationships
younger features cut across older features
Not near the headwaters
§ Gradient is less steep § Discharge is High § Competence is Low (Sediment is coarse) § Channels are not straight § Channels are smooth § Channels are wide § Factors are generally Opposite near the Stream's base level.
Near the headwaters of the stream
§ Gradient is steep § Discharge is low § Competence is high (Sediment is coarse) § Channels are straight § Channels are rough § Channels are narrow Factors are generally Opposite near the Stream's base level.
Types of artesian wells
§ Nonflowing - pressure surface is below ground level § Flowing - pressure surface is above the ground § Not all artesian systems are wells, artesian spring also may exist
What is an aquifer? An aquitard?
· Aquitard - an impermeable layer that hinders or prevents water movement (clay) · Aquifer - permeable rock strata or sediment that transmits groundwater freely (sands and gravels) Saturated subsurface rock
Where And How Fast Will Groundwater Move?
· Exceedingly slow - typical rate of movement is a few centimeters per day · Energy for the movement is provided by the force of gravity
Briefly list and describe the agents that metamorphose rocks
· Heat · Pressure ØPressure (compression) and Shear Stress · temperature/Pressure · hydrothermal fluids
From where is the heat derived to metamorphose rocks?
· Lava flows/magma · And geothermal gradients AKA heat due to depth
Why are index fossils so important?
· Time indicator · They help in the interpretation of geologic past · They allow for the collation of rock in different places
Burial metamorphism
· associated with very thick sediment layers in sedimentary basin · required depth varies depending on prevailing geothermal gradient · low grade non foliated rocks generally result
Impact shock metamorphism
· caused when high speed meteorites strike earth · products are called impactites
Hydrothermal metamorphism
· chemical alteration caused when hot, iron rich fluids called hydrothermal solutions circulate through fissures and cracks that develop in rocks · most widespread along the axis of mid ocean Ridge systems where cold seawater seeps into rock
Dynamic metamorphism
· curves alongside fault zones at depth and high temperatures - docile flow · pre-existing materials recrystallized by sharing with little to no change in temperature and pressure.
Regional metamorphism
· produces greatest quantity of metamorphic rock and is associated with mountain building · protolith undergoes an increase in temperature pressure and differential stress · rocks are foliated and grade varies with depth · rocks may display zones of contact and or hydrothermal metamorphism
contact or thermal metamorphism
· resulting from a rise in temperature when magma invades a host rock · A zone of alteration called an aureole forms in rock surrounding the magma (near surface environments) with higher grade near pluton, decreasing outward
correlation
A measure of the extent to which two factors vary together, and thus of how well either factor predicts the other.
Wadati-Benioff zone
A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary.
artesian well
A well in which water rises because of pressure within the aquifer
What is an isotope and how do they differ in relation to each isotope of the same atom?
An isotope is the same element that varies and the number of neutrons in relation to one another resulting in a slightly different mass number then the parent Adam
unconformity
An unconformity is a surface between rock layers which represents a gap in geologic time not represented by rock formations. These gaps mean rocks were either not deposited, or were subsequently removed by erosion. There are different types of unconformities.
inclusions
Any rock that is included within another rock must be older than the rock it has been incorporated into. This applies to grains within sediments, fossils, and other inclusions.
isotope
Atoms of the same element that have different numbers of neutrons
Name and define the four types of seismic waves. Which are surface waves, and which are body waves? Identify which travel fastest, have the greatest amplitude, and create the most damage. Note the apparent motion of each wave. (E.g., which waves are associated with push-pull movement?)
Body Waves P waves push-pull S waves Side to Side Surface Waves - Most Damage L waves Side to Side R waves Up and Down
What factors lead to the variation of the water table surface level?
Changes in precipitation The Seasons Usage rate
Where are deep earthquakes located geologically? Shallow earthquakes? Think plate tectonic settings and earthquake zones.
Deep earthquakes are normally located in conversion plate boundaries where one plate is subducting under another this causes there could be both shallow and deep earthquake in these locations this is unlike divergent and transitional boundaries because both of these boundaries only experience shallow earthquakes
Describe a drainage basin.
Drainage basin - land areas that drain into a stream or body of water.
During metamorphism, a parent rock fully melts, partially melts, or remains essentially solid?
During the whole process metamorphic rocks remain essentially solid
radiometric dating
the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products
Hydraulic gradient
the water table slope, determined by dividing the vertical difference between the recharge and discharge points by the length of flow between these points
What type of stress (pressure) is associated with foliation?
those that are foliated because they have formed in an environment with either directed pressure or shear stress, and those that are not foliated because they have formed in an environment without directed pressure or relatively near the surface with very little pressure
permeability
Ability of rock or soil to allow water to flow through it
Describe the relationship between velocity and competence.
Competence is the maximum size of load that a river can carry, and this is largely determined by velocity. The higher the Velocity the Higher the competence
What is the difference between competence and capacity?
Competence: Max. particle size a stream can transport.(determined by velocity) Capacity: Max. load A stream can transport (determined by competence And discharge)
Most metamorphism occurs along which plate boundary type?
Convergent plate boundaries and subduction zones
Which seismic waves travel through solid, liquid and/or gas? What does this characteristic influence? What does this tell us about the layers of the Earth?
I recommend that you start with S-waves. We know how fast S-waves travel and that they only travel through solids. Since S-waves are not recorded on the side of Earth opposite the earthquake, we can safely say that there is a liquid layer within Earth that is reflecting the S-waves and creating a shadow zone. Therefore S-waves tell us that there is a liquid layer within Earth. (We even know the size based on the size of the shadow zone - remember 103 degrees?) So how do we know that there is a liquid outer core AND a solid inner core. Thanks to P-waves. P-waves travel through solids, liquids and gases. Scientists also know how fast P-waves travel through each of these states of matter. Faster through solids than liquids. Since P-waves arrive at recording stations on the side of Earth opposite the earthquake faster than expected if only travelling through a liquid core, then we can say that there is a solid inner core that speeds up the waves. We also see a P-wave shadow zone resulting from the refraction of the waves as they move from a liquid to a solid. Therefore P-waves confirm the liquid outer core and the solid inner core.
Pressure
Increases with depth n Confining pressure applies forces equally in all directions (minerals/grains become smaller and more dense. of overlaying (sed.) layers of rock. Generally metamorphoses in tandem with temp!
turbulent flow
Irregular flow with random variations in pressure.
Define the water table!
Is a planar boundary that is the upper limit of the zone of saturation
Which seismic waves travel through solid, liquid and/or gas? What does this characteristic influence? What does this tell us about the layers of the Earth?
P waves are able to travel through liquids S waves can't travel through liquids The speed in which each of the waves can hit the opposite side of the planet this confirms to us that there is a outer liquid core and an inner solid core within the earth.
What factors influence the storage and movement of groundwater? (Hint: both terms begin with the letter 'p.'
Porosity Permeability
Define the 'rules' for determining relative time. (E.g. Law of Superposition, Original Horizontality, Cross-cutting Relationships, etc....).
Principle of Original Horizontality - all strata layers are deposited horizontally Law of Superposition in an undisturbed sequence of layers the oldest layers at the bottom and the youngest layers at the top this applies to rocks deposited such as sedimentary and lava flows principle of cross cutting relationships cross cutting relationships means that a that fractures that cut across rock layers or layers of sediment must be younger than the future it cuts this applies to fractures, faults intrusive igneous, formations
Which type of absolute dating allows for the dating of a wider range of rocks (old and young; not just young or not just old) - Radiometric or Radiocarbon? Why?
Radiocarbon dating relies on the presence of carbon 14 in fossils which is accurate to an age of about 50,000 years this is different to radiometric dating which relies on other isotopes they have a much longer half-life which allows for a wider range in the ability to date events.
What is the relationship between base level and erosion, and base level and deposition?
Raising base level causes deposition Lowering base level causes erosion
seismograms
Records obtained from seismographs
in what type of rocks (sedimentary, igneous or metamorphic) are fossils found?
Sedimentary and metamorphic
liquefaction
The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud
radioactivity
The process in which some substances spontaneously emit radiation
earthquake
The shaking that results from the movement of rock beneath Earth's surface.
tensional stress
The type of stress that tends to pull a body apart.
Define discharge.
The volume of water flowing past a given point over some period of time.
What tools and procedure are utilized to locate an epicenter of an earthquake?
Through the measuring of the time between when the first P wave arrives and the first S wave arrives in three different earthquake centers it can the location of the earthquake itself can be determined.
Principle of Original Horizontality
layers of sediment are generally deposited in a horizontal position
half-life
length of time required for half of the radioactive atoms in a sample to decay
seismographs
measures and records earthquake magnitude based on the energy released in an earthquake.
Burial metamorphism
metamorphism due only to the consequences of very deep burial
What is sediment load and how it may be divided within a stream
o Dissolved Load § The dissolved load is those minerals chemically dissolved in the water. o Suspended Load § Suspended load refers to grains of sediment that are carried by the stream without hitting the stream bed. These are generally smaller grains. o Bed Load § The bed load is the larger grains that are in saltation · Saltation o (bouncing) · Traction o (dragging).
Porosity
percentage of total volume of rock or sediment that consists of pore spaces
geologic time scale
scale used by paleontologists to represent evolutionary time
bed load
sediment that is carried by a stream along the bottom of its channel
To what type(s) of rocks (sedimentary, igneous or metamorphic) do the Law of Superposition and Principle of Original Horizontality apply?
sedimentary and igneous
body wave
seismic waves that travel through the Earth's interior
Describe common sources of groundwater contamination.
sewerage, highway salt fertilizer, pesticides, chemicals, and industrial material
Principle of Superposition
states that in undisturbed rock layers, the oldest rocks are on the bottom and the rocks become progressively younger toward the top
shear stress
stress that occurs when forces act in parallel but opposite directions, pushing parts of a solid in opposite directions
What is a protolith?
the original rock from which a metamorphic rock formed
