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CLEMSON / Geology / GEOL 101 / What are the requirements for radiometric dating?

What are the requirements for radiometric dating?

What are the requirements for radiometric dating?

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School: Clemson University
Department: Geology
Course: Physical Geology
Professor: Coulson
Term: Spring 2016
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Name: TEST 2 Geology StudyGuide
Description: Of the two study guides uploaded, this is the better one. I'm not sure what happened on the other one, but the last page didn't format properly. If you already bought the other one, contact me (slgreen@g.clemson.edu) and I'll send you the fixed one! Test is thursday so study away guys!
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Study Guide Test 2


What are the requirements for radiometric dating?



Lecture 5  

∙ Sediment: most common type of rock

Sedimentary Processes

1. Weathering

a. Parent rock breaks down into particles

called sediment

Two types of weathering:

a. Physical

∙ Plant roots: split rock as the plant

grows

∙ Frost wedging: water gets into crack  


What are the atoms of exact same element with different number of neutrons present?



 freezes  ice expands  splits rock  

 repeat

b. Chemical

∙ More common

(ex) feldspar +H2O+H2CO3

kaolinite + dissolved ions  

∙ Saprolite Formation: substance that

has undergone extensive chemical

weathering (translates to “rotten

rock” because it falls apart easily)  

2. Erosion

a. Requires energy to transport from A to B

(ex: water, wind, glaciers, gravity like landslides)

3. Deposition


What is the chemostratigraphy?



If you want to learn more check out What is an antithesis in english?

a. Basin: any place that can be filled with

sediment

b. Accommodation space: measurement

of how much sediment can fit in a

basin

c. Subsidence: when the ground level in

a basin sinks downward because of

weight from sediment thus creating

room up top for more sediment  

4. Lithification

a. Compaction: sediment gets compact as layers are added to basin  **Layers also referred to as strata or beds

b. Compaction fills the caps between the stratum of sediment  c. Cementation: when the constant compaction pushes absorbed water out  of the sediment layers and leaves behind little crystals that act as natural  cement

Classification  

1. Detrital (aka clastic) sediment  created by physical weathering  a. Gravel

b. Sand  

c. Silt  

d. Clay  

Traits of Detrital Material  

∙ Sorting: how uniform the grain size is indicates how long the erosion process was

o Long erosion = well sorted (close to same size)

o Short erosion =poorly sorted (all different sizes)

Poorly sorted If you want to learn more check out How does secondary victimization occur?

∙ Rounding: how round the grain is indicates how long the erosion process was

o Long erosion = well rounded

o Short erosion = jagged, poorly rounded  

Identifying Clastic Sedimentary Rocks

Well  

∙ Grain size is key  pick out the dominate grain size Don't forget about the age old question of What are the 14 parts of a microscope?

rounded

o Ex: sand = sandstone

o Ex: silt = siltstone

2. Chemical Sediments  

a. Form via chemical reactions  

∙ Dissolution and re-precipitation

∙ Saltwater evaporation  

b. Crystal structures

c. Usually comprised of 1 major mineral type:

Ex: halite = salt rock

Ex: quartz = chert

d. Economically viable: high concentration of one mineral so easy to find if  looking for that specific mineral without the processing costs

3. Biogenic Sediments:

a. Sediment particles come from living organisms  

(ex: shells, partially decayed plants, microscopic organisms)

i. Chalk: poorly cemented  

ii. Limestone: well cemented, tiny shell fragments

iii. Coal: compressed plant material  

Mass Wasting (landslides)

Slope Destabilization Factors Don't forget about the age old question of What is an example of syllogism?

∙ Angle of repose: max avg. number of steepness before whatever is added to  the top just falls back down

∙ Lack of Moisture: low water content/dry We also discuss several other topics like Where does somatic recombination occur?

∙ Excessive moisture: too much moisture turns sediment into mud with  landslides easily

∙ Lack of vegetation: plant roots stabilize slopes and hold sediment in place

∙ Excessive vegetation: too much vegetation can (1) add too much mass to a  steep slope, (2) absorb too much water and make soil dry, (3) roots make  channels for water to travel down

Types of Mass Wasting/Landslides

∙ Categories based on:

o Material: sediment or mud or rock or snow or ice

o Type of movement: rolling/sliding/flowing/falling

downhill

o Speed: rapidly or gradually  

1. Rockslides:  

a. Fast, but not as fast as other materials b/c of

friction between the ground and the rock

2. Creep:  We also discuss several other topics like What does long term potentiation do?

a. Sediment moving slowly downhill

b. Barely noticeable  

Ex: fence on hill starts to lean downward because

sediment is moving downhill

Causes of Mass Wasting

∙ Thunderstorms/heavy rains  

∙ Earthquakes

∙ Human Landscaping

∙ Clear cutting

**Risk Management Maps are updated frequently to determine how at risk  certain areas are for mass wasting

Preventing Mass wasting

∙ Drainage control: adding pipe systems to prevent over saturation of ground  ∙ Decrease slope grades: flattening hills to decrease the speed of run off  ∙ Building codes: like not allowing big houses to be build in steep hills ∙ Retaining walls : concrete barriers to block falling rock from reaching roads ∙ Rock Bolts: drive bold through rock into rock behind it to hold the outside  rock in place

**Prevention Cost: expensive to build/implement changes, but damage is more  costly  

estimated return is $10-$2,000 per $1 spent on prevention

**Case Study  1983 slide caused $200 million in damage, but could have been  preventable if $0.5 million had been spent on drainage systems  

Lecture 6

Metamorphism (very slow process)  

∙ Metamorphic rocks help understand the geographic history of an area

Temperature

∙ Geothermal gradient: how fast

the temp go up with depth in

the earth (varies)

∙ Avg: changes 30°C/km  

∙ Typical range: 20-60°C/km

Metamorphism via Heat

∙ Contact metamorphism: rock undergoes metamorphism due to direct heat  from magma coming towards the surface

o Primarily temp driven

o Limited in scope/only occurs close to magma

Pressure

** Note: 1 bar= 1 atm at surface of the earth

∙ Pressure gradient: ~300 bar/km depth

Types of Pressure

1. Confining pressure: rock is feeling equal

pressure from all directions

a. (Ex) swimming underwater

2. Directed pressure (aka differential): the

majority of the pressure is being applied

in a specific direction

a. Compressional

How much pressure is needed?  

∙ Most metamorphic rocks from at 10-30  

km (aprox. 1- 1.6 mi) depth (mid-lower crust)

Exposure

∙ How metamorphic rocks get back to the surface  

o Faults  rocks on either side of fault move/broken down thorough  weathering and erosion  

Types of Metamorphism

Via Pressure

o Regional metamorphism: large scale process/opposite of contact  metamorphism  

o Contact metamorphism: INSERT DEFINITION  

o Fault metamorphism: occurs on a small scale along the fault line.  Pressure is still the primary driver

Via Fluid  

o Metasomatism: rock comes in contact with very hot ground water.  Water flushes things out of the rock or deposits new minerals that  change the mineralogy  

 Ores: high concentration of a specific mineral  

o Seafloor metamorphism: almost always forms basalt. specialized in  environment where the cold seawater interacts with the rock  

Metamorphic Change

∙ Metamorphic grade: measures metamorphic change due to change in temp  and pressure  

o Low, intermediate, high

o Doesn't tell you anything specific/needs to be better differentiated  ∙ Index minerals: a mineral can help identify the correct metamorphic grade o Each index mineral is formed in very specific environment  

∙ Metamorphic Facies: group of index minerals that form at the same temp and pressure

o Ex) blueschists facies includes the minerals glaucophane, lawsonite,  epidote

7 Major Metamorphic  Facies

**Facies used to reconstruct how metamorphism occurred

Length of  

Metamorphism

∙ Prograde: temp and pressure are climbing towards peak or metamorphic  grade in rock history

∙ Retrograde: temp and pressure are

decreasing after they have already

peaked in rock history (usually due to

reaching the surface)

** We need to figure out the time frame of

each period  

∙ Changes within minerals can record

Pressure-Temp changes  

o Un-uniformity allows for tracking

o Crystal grows outward with rings

like a tree trunk  

Types of Metamorphic Rocks

1. Foliated Metamorphic Rocks

a. Slate

b. Schists: hard to identify (samples

can vary drastically)

c. Gneiss (pronounced “nice”)

*these rocks are formed from different pressures

2. Non-foliated:

a. large crystals

b. high concentration of one specific mineral

c. appearance is very similar so you cannot eyeball the identify  i. Hornfels  

ii. Quartzite  

iii. Marble  

Geology in the News: sudden volcanic eruptions found to trigger from gas bubbles  in magma

Structural Geology: Focuses on how rocks deformed after they've been created  = rock deformation

∙ Note: Topographic (landscape) features and geologic structures are very  different

Tectonic Forces

1. Tensional: stretching an object (pulling away from the center in two  directions)

2. Compressional: the area is getting squeezed or compacted

3. Shearing: material getting slid in two different directions at the same time

Responses to stress:  

∙ Brittle: break with enough force ∙ Ductile (aka plastic): bend away from force

∙ Response can vary based on:

o Rock type, temp/pressure, speed of deformation (faster the application, the more brittle the response)

Types of Structures

∙ Folds: formed with a ductile response to a compression force

*Know limbs  

and hinge  

(where all the  

motion seems  

to be  

occurring)

Classifying Folds

1. Shape (in road cut or cross-section view)  

Anti

a. Antiform: anti-smilie face (frownie face)

b. Synform: smilie face c. Overturned:  

i. Overturned Antiform

Syn

ii. Overturned Synform  

iii. Overturned  can’t tell if Antiform or Synform  

Overturned  

synform

Overturned Overturne

d antiform

2. Age of

Layers relative to each other

a. Anticline: oldest layer in the center fold between

the limbs

b. Syncline: the

center fold

layer is the

youngest rock

**This happens because  tectonic forces can cause an entire stack of layers to get turned upside down

3. Geometry:  

a. Horizontal: squeezed in from both sides and nothing else (looks  horizontal in birds eye view)

b. Plunging: squeeze from both

sides and tipped up or down

(more common)

Types of Structures ∙ Joints: brittle response

Antiform,  Anticline,  Plunging

Synform, Syncline, Horizont al

o Most common type of geologic  structure  

o Tend to occur in sets

o Can have more than one joint set within rock body

∙ Faults: brittle response of cracking and then move/shift in different directions o Different sizes: from a couple of inches to 100s of miles

o Classified by slip direction  

Types of Faults:  

1. Dip Slip Fault: inclined fault plane, vertical motion, one side up and one side down

**Picture yourself walking down the fault line  the side your feet would touch = foot wall  

a. Normal Dip Slip: when the hanging wall is lower, and the footwall is higher

b. Reverse Dip Slip: when the foot wall is lower, and the hanging wall is higher

Reverse

Normal Reverse

c. Thrust

Fault: hanging wall higher

than foot wall (not a steep

incline, occur at subduction

zones)

2. Strike-Slip Faults: horizontal

movement (parallel to the fault

plane)

a. Left-lateral: no hanging/foot

wall, each side thinks the other moved to the left  

Top layer has slid up  on top of bottom layer

b. Right lateral: each side thinks the  other side moved to the right  

Faults and Forces

∙ Compressional: hanging wall slides up line

∙ Tensional: hanging wall slides down line

∙ Shearing force: hanging wall moves to side  

Lecture 7

Geology in the news: 6.4 magnitude earthquake in Southern Taiwan ∙ Apartment building fell over

∙ Several dead and 100 missing  

∙ Chinese new year celebrations cancelled

Earthquakes: build up of energy along a fault or plate margin  1. Stress < Friction

2. Stress ~ Friction (energy has built up, but still no movement, elastic  deformation=rock starts to

bend)

3. Stress > Friction (plates

move)

Earthquake Frequency  

∙ Small earthquakes are quite common

o Aprox. 1 million quakes with a magnitude of 2 per year ~ 2,740 per  day

o Only about 10 quakes with a magnitude of 7per year

Power of Earthquakes

Earthquake Movement

∙ Focus: underground point where the movement occurs on the fault in the  earthquake

o The center fault may not

move

o Many foci are only 2-20 km

deep in continental crust

(usually not any deeper b/c

the rock has to be brittle for

earthquakes to occur)

∙ Epicenter: geographic point on the

surface of the earth directly about

the focus

∙ Foreshocks: small movement that

occurs before earthquake to try to

relieve some of the built of energy  

∙ Aftershocks: small movements that

relief the rest of the energy after

earthquake

Seismic Waves

∙ Seismic waves: waves which the energy of an earthquake moves away from  focus

Three Types

1. Primary Waves (P waves): push/pull

or compressional waves, fastest

wave (6 km/s, 20x faster than the

speed of sound), can move through

both solids and liquids

a. Ex) moves like a slinky or like

a caterpillar

2. Secondary Waves (S waves): shear

waves, vertical motion, slower

(about half the speed of p waves),

cannot move

through liquid  

a. S wave

shadow zone:

area where s

waves can’t

get to (where

the red lines

don't reach in diagram)

3. Long Surface Waves (L waves): vertical and lateral motion, restricted to  the surface of the earth

Measurement and Detection

∙ Seismometer (aka seismograph, the outdated name): tool to detect  earthquakes

Three myths about seismometer:

1. It’s a solo machine: acutally needs 3 seismometers minimum (one  calibrated for E/W, one calibrated for N/S, one calibrated for Up/Down or z  axis)

2. Old fashioned looking machines in movies: those are outdated everything is done digitally now  

3. Swinging needles: the pendulum used for drawing waves doesn’t actually  move, but the machine itself does (pendulum isn’t used anymore,  

everything digital)

Finding the focus:

∙ P waves arrive , then S waves

arrive

*Understand how this chart is

used

Measuring Damage  

1. Mercalli Index: scale that

measures how much

damage/destruction the

earthquake caused  

a. Uses roman numerals

(I=lowest grade of damage)

b. Not used by scientists b/c

doesn't account for how

populated the area hit was

c. Easier to manipulate for

insurance companies

2. Richter scale: measures the amount of shaking (Charles Richter 1935),  logarithmic scale

a. Not typically used by scientists

3. Moment magnitude: the amount of slip that occurs on the fault a. Easier to calculate  

b. Can be measured based on field data

c. Best for scientific use

Quakes and Plates

∙ Faults are along plate boundaries

o So, earthquakes occur near plate boundaries

o Deep earthquakes occur along subduction zones

∙ Because of this trend  risk assessment maps are made  *Some quakes can still occur far from plate margins  

∙ But predicting earthquakes is difficult because every fault is different  o Diff rocks/plate motion/forces

o No magic formula to calculate when an earthquake will occur Damage Control

∙ Land Use Policies:

o Ex) 1972 California Law made it illegal to build on the fault ∙ Building Codes:  

o Make sure buildings are stable so there is less damage  Ex) Tall buildings can’t be built along fault lines

∙ Site Selection:  

o Solid rock is best to build on b/c of stability  

∙ Liquefaction:  

o Loose sediment contains a lot of water, when seismic waves goes  through the sediment, it creates mud  

∙ Earthquake myth:  

o Rocks will crack open and swallow your entire house

Lecture 8

Geology in the news: tin cans found within the walls of collapsed buildings after  Taiwan earthquake  

Dating Methods

∙ Relative dating: putting together a sequence to know what came 1st, 2nd, and  3rd  

o Ex) Dinosaurs existed before humans  

o Cost effective/essentially free/easier

∙ Absolute dating: putting numbers on actual events  

o Ex) dinosaurs went extinct x million years ago

o Can be expensive/more difficult/not always important

Relative Dating

∙ Fossils: any evidence of past life forms

o Footprint, plant impression, sea shell, etc

o Mainly found in sedimentary rock

Stratigraphy: subset of geology (predates) study of strata or layers of rocks  ∙ Unconformities: breaks or gaps in time records where not all the time periods are represented in the layers of rocks (example on right)

o Gap occurs when…

 Sediment deposits runs out or no other layers are formed during  that time

 Run out of accommodation space (basin

becomes full)

 Eroding sediment faster than it is being

deposited  

Three types of Unconformities

1. Disconformity: sedimentary rock on one side of

gap and a diff type of sedimentary rock on the

other (black line=gap)

2. Nonconformity: sedimentary rock on one side of

the gap and igneous or metamorphic on the other  

**study tip: nonconformity = not the same

3. Angular unconformity: layers underneath gap come up and strike gap  at an angle (takes a long time to develop)

Two Problems with Unconformities

1. Identification: hard to find the gap

2. Duration: hard to find out how much time is past

Stratigraphic Principles

1. Principle of Original Horizontality: layers of sediment originally form as  a horizontal line

2. Principle of Superposition: when looking at a stack of layers, the one on the bottom is the oldest and layers above get younger

3. Principle of Cross-Cutting Relationship: whatever did the cutting is the  youngest

4. Principle of Faunal Succession: fossils seen in different layers are  always going to occur in a set pattern (the oldest rocks contain oldest  fossils)  

a. Correlation: linking two places together to see how old the rocks  are in relation to one another  

Example: correlation found via faunal succession

Correlation with Fossils

∙ Not all fossils are great for correlation  

o Want to identify short spans of time (more precision=stronger  correlation)

o Smaller, inconspicuous fossils usually better

∙ Index (or guide) fossils: ideal fossil to use for correlation  

Four Qualifications to be index fossil:

1. Were numerous:  

a. a lot of them don’t get fossilized, so a bigger population increases  chances of fossils  

2. Widespread:

a. The more places it lives in, the more places that can be correlated  together

3. Went extinct quickly:  

a. “Die as fast as you can.”  

b. Precision = stronger correlation (cockroaches are a bad index fossil  b/c they’ve been around forever)

4. Easy to identify: to insure you’re comparing the same fossils  

Other Correlation Tools:  

∙ Some places don’t have index fossils to use, so there are other dating  methods

∙ Lithostratigraphy: correlations based on rock types

o Decent at starting correlation but too many underlying factors to  finalize correlation

∙ Sequence Stratigraphy: correlation based on pattern/sequence of  unconformities

o Beneficial to oil and gas industry b/c costal areas are ideal for  sequence stratigraphy  

∙ Chemostratigraphy: chemically correlate areas  

o Ex) Iridium anomaly at the Cretaceous-Tertiary boundary: meters and  asteroids have a massive amount of  

iridium so there must be a connection  

there  

∙ Magnetostratigraphy: magnetic signature  

that get recorded in rock layers  

o A little rough on the eyes: like trying to

take two bar codes and slide them  

around until you can find matching  

black and white stripes  

Geologic Time Scale

∙ Originally built via stratigraphy  

∙ Fossils were the key for defining boundaries

Eons

1. Hadean: 1st billion years of the earths

existence  

a. 4.5 Ga-4.0 Ga  

b. Density stratification period  

c. Earth’s earliest atmospheres/oceans

form

2. Archean: continent building  

a. 4 Ga – 2.5 Ga (about ½ billion years

long)

3. Proterozoic: oxygen build up in the

atmosphere for the first time  

a. 2.5 Ga - 550 Ma

4. Phanerozoic: curretnt eon we’re living in

where Fossil records are at its best

Three Phanerozoic Eras

1. Paleozoic (550-200 Ma): translates to “ancient life”

a. Cambrian Explosion: a sudden burst of new organisms on  

the scene

2. Mesozoic (200 Ma – 65 Ma): dinosaurs  

3. Cenozoic (65 Ma – now): includes the ice age

a. Mammoths became dominate species  

Geology in the News: new info on why quake occur deep in subduction zones  water released from mineral called lawsonite reduces friction and enables the fault  to move despite the high pressure environment  

Absolute Aging

Two Approaches:  

1. Non-radiometric: involve zero radiation

2. Radiometric: involve radioactive materials  

Non-radiometric Methods

1. Varves: type of sediment deposits  

a. Thin layers that alternate light and dark bands that only form under  certain conditions (counting bands tells how long the climate in the  area has met the proper conditions)  

i. Light color  normal sediment deposits during warmer months  ii. Dark color  when lake ices over and additional sediment not  added to water, but sediment floating in water settles and gets  deposited  

***Note: Varves only form if nothing disturbs the sediment  

(crabs, snails, creatures of that nature)

2. Dendrochronology:  

a. Counting the growth ring in trees (1 ring = yr, dark rings= tree had  stopped growing)

i. Note: some species of trees don't form rings yearly (some more  than one ring per year or some less than one ring per year)

ii. Forest fires can stop the trees from growing  

b. Used to learn about area and its environment  

i. Climate can affect if the tree grows quickly or slowly  

ii. Cross Reference trees with each other to get an extended time  lie  

Radiometric Dating  

∙ Isotopes: atoms of exact same element with different number of neutrons  present  

o Radioactive isotopes: neutrons that are weighed unstable

∙ Radioactive Decay: radioactive atoms will break down to become more  stable  

o Parent Isotope: before decay

o Daughter Isotope: after decay (***can have multiple daughter  isotopes)

***Note: there is no way to predict when an atom will start decaying,  but the rate of decay is known so once decay starts, can predict when  the process will end.

∙ Radiation: emitted energy  

∙ Decay Series (aka chain): multiple steps/daughters of decay to become  stable  

∙ Half-life: the time it takes for half the current atoms to decay (# of parents  divided by 2)

Half-lives don't vary with any environment factor.

o Th-234 = 24.1 days

o Pb-210 = 22.3 years

o U-238 = 4.4 billion years

∙ Radiometric techniques are created/improved by first dating things that we  already know the age of (ex: Egyptian mummies)

Requirements for Radiometric Dating:  

1. Radioactive isotopes must be present in the specimen  

2. Must have both parent and daughter atoms in specimen

a. If only parent atoms  decay hasn't started

b. If only daughter atoms  decay is already finished  

3. Can only go so far back in time

a. Usually can go max 5 isotopes back until parents atoms eventually  runs out

4. Closed System: not interactive with its surroundings  

a. No parents or daughter isotopes to be added or subtracted  i. Add parents/lose daughters: looks like little time has passed ii. Add daughters/lose parents: looks like more time has passed Case Study of Carbon 14  

C-14  N-14 + particle + energy (carbon 14 decays to nitrogen 14) ∙ Half life of C14 = 5,730 years

o Can track back to 10 half-lives

o Extremely sensitive  

∙ Earth hasn't run out of C-14 because this reaction…

o Cosmogenic ray + n0 + 14 N 14C + p+ 

o C-14 globally distributed because atmospheric reaction all around the  world

o Amount decaying = amount produced  

 Some isotopes do go extinct because they’re not reproduced Carbon Dating

∙ Carbon dating can only go back so many year and can only work for certain  materials (doesn't work for rocks/minerals)  

o Animals are exposed to C-14 through the food chain

 C14 + O2 = 14CO2 in atmosphere, plant filters the 14CO2, the  animal eats the plant, and from there after, everything in the  

food chain is exposed to C14

 When the animal dies, it becomes a closed system because no  parent atoms added by eating

 Some organisms don't get carbons from the atmosphere or food  chain

Decay Equation

∙ Age = [ln(Nf/N0)/-0.693]*half-life

o Nf/N0 = % 14C in the sample relative to amount found in living tissue  (i.e., how much parent is left)

Ex: fossil still has 10% of its 14C

Age = [ln(0.10) / -0.693) * 5,730

Age = 18,940 years old

Assumptions for Carbone-14

1. System remains closed after death

a. Not true  extra tests are required to ensure specimen was a closed  system

2. Amount of C-14 in living tissue doesn't vary through time

a. Not true…

i. C-14 production varies based on solar cycles but variations are  small/on short timescales  

ii. Fossil fuel burning changes the amount of C-14 in the  

atmosphere (scientists already took into account this change and fixed their methods)

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