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CLEMSON / Geology / GEOL 1010 / What is the most common rock on earth’s surface?

What is the most common rock on earth’s surface?

What is the most common rock on earth’s surface?


School: Clemson University
Department: Geology
Course: Physical Geology
Professor: Alan coulson
Term: Fall 2015
Tags: Physical Geology and Geology
Cost: 50
Name: Geology EXAM 2 Study Guide
Description: This study guide covers what will be on the second exam for Physical Geology taught by Dr. Coulson
Uploaded: 02/21/2016
13 Pages 85 Views 17 Unlocks

GEOL 1010 ­ Dr. Coulson ­ TEST 2 STUDY GUIDE

What is the most common rock on earth’s surface?

Highlight = Important Principle Highlight = Key Term

Lecture 5: ​Sedimentary Rocks and Processes

Forming Sedimentary Rocks

­ sedimentary rocks are the most common on on earth’s surface

­ used in construction, in energy resources, where fossils are found

­ Parent rock ­ original rock/pre­existing rock

­ Formation

1. Weathering ­ breaking down rock

a. physical weathering ­ physically breaking down rock

i. ex: plant roots breaking up rock

ii. frost wedging ­ water between cracks of rocks freezes in low temps and

What are the 3 main categories of sedimentary rocks?

breaks apart rocks

­ potholes can be a result of this

b. chemical weathering ­ chemical reaction breaks down the rock

i. more common in nature

ii. ex: Feldspar + H₂O + H₂CO₃➡Kaolinite + dissolved ions

iii. ex: Saprolite formation

2. Erosion ­ carrying of sediments (transport process)

a. requires energy

b. 4 ways of transportation

i. water (very common)

ii. gravity (rocks rolling down a hill)

iii. wind (sand blowing at a beach)

iv. glacier ice (less obvious, but still common)

How metamorphic rocks get to surface?

3. Deposition ­ depositing sediments in new place If you want to learn more check out What is expropriation risk?

a. basin ­ any place you can deposit sediment

b. accommodation space ­ volume of space for sediment to be deposited

c. subsidence ­ sinking of land into a basin

d. Layers (strata, beds)

4. Lithification ­ getting sediments and compacting them into one rock

a. cementation ­ solidifying fusion of sediments by compacting the rocks together i. water gets pushed out and deposits wet minerals, which act as the cement

to bind the rocks and minerals together


­ 3 main categories of sedimentary rocks Don't forget about the age old question of What does fat provide energy for?

1. Detrital (aka clastic) sediment ­ mainly physical weathering

a. ‘how big are the sediments?’

b. sorting ­ ‘how uniform is the sediment size’ (well­sorted, moderate, poorly­sorted?) i. improves as time progresses

c. rounding ­ roundness of minerals within rock

i. improves as time progresses

2. Chemical Sediment ­ form via chemical reactions

a. dissolution and reprecipitation

b. saltwater evaporation

c. usually comprised of one major mineral type

i. ex: halite = rock salt, quartz=chert

d. economically viable

3. Biogenic Sediments ­ used to be parts of plants/animals

a. ex: shells (large or microscopic), coral, etc

b. ex: chalk, limestone, coal

Mass Wasting (Landslides)

­ important due to danger of occurrence

­ angle of repose ­ max angle where a slope is stable

­ typically 35°, but always check!

­ slope destabilization

­ lack of moisture (only dry sediment leads to difficult in compactness)

­ too much moisture

­ lack of vegetation ­ plant roots are good at holding things in place, so lack of them leads to lack of holding things in place

­ excessive vegetation ­ roots can also form natural pathways for water to run down, and plants are heavy and could fall/slide If you want to learn more check out Define physical anthropology.

­ types of mass wasting (based on material, type of movement, and speed)

­ ex: Rockslide ­ rocks sliding down at a moderate speed

­ creep ­ slope is unstable, and rocks are sliding very slowly

*NOTE: ​unstable slope does not automatically mean landslide*

­ Causes of Mass wasting

­ lightning, earthquakes, deforestation, etc. are all causes If you want to learn more check out Characterize aristocratic resurgence.

­ Risk Assessment Map ­ assessment of an area that shows dangerous spots

­ adjustments are constantly made: landslide patterns change constantly

­ Prevention:

­ Drainage Control

­ decrease slope grades

­ building codes

­ retaining walls

­ rock bolts


­ although all of these prevention measures could be costly, the amount

of money in damage would cost much more

­ Case Study: Thistle, UT 

­ 1983 slide cost $200 million in damage

­ deemed preventable if $0.5 million had been spent on drainage system

Lecture 6: ​Metamorphism and Structural Geology

Why do we care?

­ many minerals used for technology

­ metamorphic rocks help discover history of an area

­ very slow process (could take a million years to start)

­ Temperature increase is needed for process

­ Geothermal gradient ­ how hot it gets and how fast beneath the earth at different depths ­ average geo. gradient = 30°C/km Don't forget about the age old question of Name some sexually related diseases.

­ typical range = 20­60°C/km

­ can still be higher or lower in special cases

­ high gradient = hotter temp per km

­ Metamorphism vs. Heat 

­ contact metamorphism ­ rock coming into contact with hot magma

­ ex: Plutons projectile

­ driven by temp

­ localized/small scale

­ Pressure vs. Heat 

­ 1 bar = 1 atm (atmospheric pressure)

­ Pressure gradient is about 300 bar/km

­ confining pressure ­ pressure on all sides of object, even distribution

­ ex: swimming under water

­ directed pressure (differential) ­ pressure coming from mostly one direction

­ most metamorphic rocks form at 10­30 km (mid­lower crust)

­ = 6.25 ­ 18.75 miles

­ How metamorphic rocks get to surface

­ as layers get pushed up through plate movements/faults, they soon get weathered/ eroded and make it to the surface

­ regional metamorphism ­ opposite of contact metamorphism

­ at convergent plate boundaries

­ pressure driven ­ large scale

­ fault metamorphism ­ faults occur and form metamorphic rocks If you want to learn more check out Describe the customer-supplier relationships in terms.

­ small scale, pressure driven

­ Metamorphism vs. Fluid 

­ metasomatism ­ hot groundwater interacts with rock

­ water carries things in it and could deposit some things into rocks

­ forms ores

­ seafloor metamorphism ­ close to Mid­Ocean Ridge

­ like metasomatism, but in specific area (MOR)

Metamorphic Rocks and Environments

­ Parent rock is the key to figuring out which metamorphic rock forms

­ Metamorphic grade ­ how much did the rock change

­ low­grade = low change, high grade= high change

­ not very specific; there is a lot of variation in each field

­ index minerals ­ gives range of temps/pressures for rocks

­ smaller range the better

­ metamorphic facies ­ group of index minerals that form under similar conditions ­ ex: blueschist facies include minerals epidote, lawsonite, and


­ major facies:

a. zeolite ­ lowest temp/pressure

b. Hornfels ­ high temp increase but low pressure increase

c. Blueschist ­ high pressure but low temp increase (subduction


­ low temp due to coldness of oceanic plate submerging

d. Eclogite ­ very high pressure

e. Granulite ­ starting to melt again

*NOTE:​diogenesis = before facies start (NOT metamorphic rock)*

­ Length of Metamorphism ­ large range

­ Prograde ­ portion of history when rock had increase in temp/pressure

­ retrograde ­ temp/pressure of rock began decreasing

­ changes within minerals

­ Types of Metamorphic rocks

1. Foliated Metamorphic rocks ­ sheets/layered appearance

a. ex: slate, schist, gneiss (gneiss has felsic/mafic separation)

i. not obvious: can come from different parent rocks, crystals can cover up

sheets, etc.

2. Non­Foliated Rocks ­ opposite of Foliated

a. difference from foliated is from type of pressure (confining is non­foliated, directed is foliated)

i. ex: Hornfels, Quartzite, Marble

**know examples of Hornfels, blueschist, non­foliated, and foliated**

**Geology in the News: ​‘Sudden’ volcanic eruptions found to trigger from gas bubbles in magma

Structural Geology/Tectonic Forces

­ Structural geology­study of how rocks are deformed after they are formed

­ Topographic features ­ on surface of earth (on maps); landscape

­ Tectonic forces (how rocks are formed)

1. Tensional ­ stretching object (pulling in different directions)

a. ex: divergent boundaries

2. Compressional ­ squeezing in form multiple sides

a. ex: convergent boundaries

3. Shearing ­ sliding in 2 different directions

a. ex: transform boundaries

­ Responses:

1. Brittle ­ strong/ resistant rocks shatter into random pieces

2. Ductile ­ rock can bend and is malleable

­ Responses vary based on:

­ rock type

­ temp/pressure

­ speed of deformation ­ quicker applying of deformation means more likely

to have brittle reaction, while slower = ductile

Types of Structures

1. Folds ­ ductile response to compressional force

­ happens on low/high scales

­ typically happens in groups

­ limb ­ sections of fold with pretty straight portions

­ hinge ­ where rocks pivot/turn into curvy edges in a fold

­ classifying folds (3) 

1. shape ­ cross­sectional view (aka ‘roadcut’, ‘cliff­face’)

a. antiform ­ rainbow shape

b. synform ­ u­shape

c. overturned:

i. overturned antiform

ii. overturned synform

iii. overturned

overturned antiform overturned overturned synform

2. Age of layers relative to each other

­ acticline ­ oldest layers is in between layers (center)

­ syncline ­ oldest layer on outside part of fold

*NOTE​: sometimes tectonic forces can cause an entire stack of layers to

be turned upside down

3. Geometry ­ how force was applied

­ must be seen from above and second cross­sectional views

­ horizontal ­ force applied from two sides

­ above view ­ horizontal stripes

­ side view ­ folds/layers

­ plunging ­ force applied from two sides and force applied to cause tipping up or down

­ more common in world

­ visible in above view, NOT in cross­sectional

2. Joints ­ brittle response and no other forces

­ lots of cracks (called ‘joints’)

­ most common geological structure

3. Faults ­ brittle response with movement along cracks

­ motion is relative

­ varies in sizes (1 inch to 1000s of miles)

­ classified by slip direction

1. Dip­Slip faults ­ vertical motion

­ inclined fault plane: one side clearly moves upward

­ foot wall ­ plane that has acute angle

­ hanging wall ­ plane that has obtuse angle

­ Normal dip­slip ­ hanging moved down and foot moved up

­ reverse dip­slip ­ hanging moved up and foot moved down

­ Thrust fault ­ handing goes up and foot goes down

­ only difference between thrust and reverse: thrust is

almost horizontal

­ important in subduction zones

**STUDY TIP: Don’t just memorize the pictures! You MUST identify hanging vs. foot walls to determine if it is normal or reverse

2. Strike­Slip faults ­ horizontal movement

­ no hanging/foot faults

­ left­lateral ­ relative to each other, each block has moved to the left

­ right­lateral ­ relative to each other, each block has moved to the right

**make sure that you know the orientation (birds­eye view, cross­sectional, etc)** **notice that different fault types form based on forces applied*

Lecture 7: ​Earthquakes

**Geology in the News: ​6.4 magnitude earthquake in Taiwan caused the cancellation of Chinese New Year

Why do we care?

­ Can cause a lot of damage and loss of lives

­ we can try to prevent

What is an earthquake?

­ when two plates move past each other, energy builds up

­ Time 1: Stress<Friction Plates Stationary

­ Time 2: Stress~Friction Elastic Deformation

­ Time 3: Stress>Friction Plates move

­ energy builds and process repeats itself

­ small quakes are very common

­ 1 million magnitude 2 quakes per year

­ category 9 energy = annual energy used in USA

­ Point of Movement

­ focus ­ where movement originates (many are 2­20 km deep)

­ epicenter ­ point directly above the focus on the surface

­ Movements before and after

­ foreshocks ­ small movements prior to the earthquake

­ in an attempt to relieve energy

­ aftershocks ­ small but bigger than foreshocks

­ not all energy has been released in main quake

­ Seismic Waves ­ waves moving away from focus (3 types)

1. P (Primary) ­ compressional motion through earth’s surface

a. alternating compression/expansion

b. 20 times faster than speed of sound

c. can move through solid/liquid

2. S (Shear)

a. added vertical range of motion

b. cannot move through liquids

c. half the speed of P­waves

d. forms shadow zone through earth

3. L (Long, Surface) ­ move along the surface

a. slowest

b. moves in vertical/horizontal range

­ Measurement and Detection

­ seismometer ­ aka seismograph (outdated)

­ Myths:

1. You only need one machine

a. you need 3: one for each axis

2. Old fashioned

a. data is almost all digital today

3. Swinging needles for amplitude

a. needle is on a pendulum and machine shakes (outdated)

­ data

­ x­axis­ travel time in minutes

­ y­axis ­ amplitude for all axes of movements

­ p waves come first, then s, then a long period of L

­ key to finding focus is different that different waves travel at different speeds ­ distance = difference between p and s times

­ draw circles with radius of this distance to triangulate focus

­ How big was the earthquake?

1. Mercalli Index ­ lower Roman numerals/little damage

a. based on damage to environment

b. not commonly used with scientists

c. for the same quake, the index will be different per location

2. Richter Scale ­ measures amount of shaking at various seismometer stations a. designed by Charles Richter in 1935

b. logarithmic scale

i. ex: a magnitude 3 is 10x a magnitude 2

c. moving between numbers is a big deal

3. Movement magnitude ­ measures amount of slip on the fault

a. easiest to calculate from field measurements/seismometer data

b. scientists prefer

­ Earthquake Locations

­ much deeper foci occur along subduction zones

­ Blueschist facies has very brittle behavior, creating huge earthquakes in these zones

­ Risk assessment maps made to indicate change of quakes

­ Predicting quakes is nearly impossible

­ Damage control

­ land use policies

­ ex: California Law (1972) ­ ‘do not build on faults’

­ building codes

­ Not building skyscrapers near fault zones

­ myth: Earth cracks open and swallows things

­ These are actually the best locations to build

­ Site selection: building on strong foundation like bedrock is the best

­ Gravels, sands and muds are worst choices

­ liquification ­ liquid inside unstable foundations lead to sinking and tipping buildings Lecture 8: ​Geologic Time

**​Geology in the News:​Tin cans collapsed between walls from Taiwan earthquake Why do we care?

­ we want to know when certain things occurred

­ 2 approaches

1. Relative ­ sequence of events; qualitative

a. not hard numbers; more like ‘this before this but after this’

2. Absolute ­ not comparative; gives exact numbers

a. can be very expensive to pay for Research, while relative is nearly free

b. can need highly qualified researchers/lab equipment

c. not always necessary

Relative Dating

­ Fossils ­ any evidence of past life on earth (skeleton, shells, footprints, etc)

­ only really found in sedimentary rocks

­ led to stratigraphy ­ study of strata

­ people wanted to know about fossils and the rocks they

were found in

­ unconformities ­ strata is rarely in continuous line (gaps/breaks in strata timeline) ­ why are there gaps?

1. run out of sediments

2. run out of accommodation space (basin)

3. start eroding sediment faster than deposition

­ types of unconformities: classified by strata above/below gap

1. disconformity ­ different kinds on top and bottom (both


2. nonconformity ­ sedimentary on one side and not sedimentary on


3. angular ­ rocks below are tilted at angle while on top is horizontal

a. complicated formation

­ problems with unconformities

­ identification ­ can be difficult to classify

­ duration ­ how much time was lost?

­ Stratigraphic Principles 

1. principle of original horizontally ­ strata is originally horizontal

2. principle of superposition ­ oldest layer on bottom, youngest on top

3. principle of cross­cutting ­ two things intersect/cut through each other

a. whatever did the cutting is the youngest formation

4. principle of faunal succession ­ fossils found in specific order

a. older fossils are on bottom, younger on top

b. correlation ­ comparing strata in two areas by age

i. not all fossils are good for correlation

ii. want to identify short spans of time

iii. index fossils ­ aka guide fossils ­ good for correlation

1. very numerous

2. widespread

3. went extinct quickly

4. easy to identify

iv. other correlation tools

1. lithostratigraphy ­ correlate layers by rock type

a. good for generalizing, but has a lot of exceptions and


2. sequence stratigraphy ­ correlation based on patterns of


a. works well in coastal areas

3. chemostratigraphy ­ correlation based on chemical properties

a. ex: Iridium anomaly at Cretaceous­Tertiary

4. magnetostratigraphy ­ looks at magnetic current

­ Geologic time scale 

­ originally built via stratigraphy

­ fossils were key to defining boundaries

­ eons ­ largest units on scale (only 3­4


1. Hadean ­ when earth formed

a. 4.5­4 Ga

b. almost no material left on

earth to study this

2. Archean ­ 4­2.5 Ga

a. when different parts of

continent formed

b. atmosphere had no oxygen

3. Proterozoic ­ oxygen begins forming

a. 2 Ga

4. Phanerozoic ­ most fossils found here

a. 3 eras

i. Paleozoic (550 Ma ­ 200 Ma) ­ vertebrates

1. Cambrian Explosion ­ large diversity change (much more)

ii. Mesozoic ­ reptiles

1. 200 Ma ­ 65 Ma

iii. Cenozoic ­ mammals

1. 65 Ma ­ now

**Geology in the News: ​new info on why earthquakes occur deep in subduction zones ­ water released from a mineral called lawsonite enables to fault to move despite high pressure

Absolute Ages ­ Quantitative Approach

1. Non­Radiometric Approach 

a. varves ­ sediment deposit ­ alternating dark/light layers in lakes

i. need top layer to freeze to become a varve

ii. each band represents different seasons

­ dark colors = winter

­ light colors = spring/summer

­ 1 light band + 1 dark band = 1 year

iii. used to find/measure times and to discover climates

iv. only gives climate data for specific location

v. can’t have mixing layers (caused by living organisms)

b. dendrochronology ­ counting rings in a tree

i. used on local scale

ii. can only go so far back in time with one tree

iii. can use overlapping to get further back in time

iv. must know what kind of tree

­ some trees don’t form annual rings

v. rings may not show due to climate issues

2. Radiometric ­ use of radiometric data for dating specimens

­ isotopes ­ atoms of same element but with different numbers of neutrons

­ labeled by atomic weight (protons+neutrons)

­ some isotopes are unstable

­ Radioactive Decay ­ emitting particles of energy to become stable

­ Radiation ­ the given off energy

­ parent atom ­ starting atom

­ daughter atom ­ atom given off

­ decay series/chain ­ multiple radioactive daughters

­ decay series ends with a stable daughter atom

­ how to measure radioactive decay: 

­ misconception ­ watching atoms ‘pop’

­ no way to know when an atom will decay

­ ex: bag of popcorn popping

­ half­life ­ time it takes half of parent atom to decay

­ decay/half­life is NOT linear; it is exponential (hence

‘exponential decay’)

­ daughter and parent atoms are equal, and add up to

original amount of parent atoms

­ every radioactive isotope has its own half­life

­ wide range

­ don’t change with any environmental factor

­ Requirements for Radiometric dating:

1. radioactive isotopes must be present in specimen

2. measureable amounts of parent and daughter atoms

a. no parent = we don’t know how long it’s been

b. no daughter = we don’t know how long it will be

3. can only go so far back in time

a. why? parent eventually runs out

i. about 5 half­lives is about as far as you can go

4. Closed system ­ specimen is not changing with environment

a. open system problems:

i. add/lose daughter = looks like very little time has passed

ii. add/lose parent = looks like a lot of time has passed

Case Study: Carbon 14 

­ carbon has 3 isotopes, only one is radioactive

14 14

­ C⟶ N + particle + energy

­ half­life: 5.730 years

­ can track through 10 half­lives

­ forming carbon 14:

­ why haven’t we run out?

­ more Carbon 14 is constantly produced in atmosphere

­ global distribution ­ can find everywhere on earth

­ steady state ­ amount created is balanced with amount decayed

­ how do we know it works?

­ start by testing what you already know the age of

­ ex: mummies in Egypt

­ what can we date with carbon 14?

­ rocks are terrible for dating with carbon 14

­ fossils and organic material is very good

­ Calculating age

N f 

ln( )

Age = half ife)

−0.693 * ( − l

N o 

N f 

­ = % carbon 14 in sample relative to amount found in living tissue N o

­ ex: Mammoth tusk has 17% Carbon 14 still present

­ answer: 21,987 years

­ Assumptions:

1. System remains closed after death

a. not good assumption

2. amount of Carbon 14 in living tissue doesn’t vary through time

­ first problem: Carbon 14 produced varies over time

­ variations are small and on short timescales

­ people don’t understand that Carbon 14 is constant (mostly)

­ second problem: fossil fuel burning has changed the relative amount of the carbon isotopes in the atmospheres

­ Limit of Carbon 14 dating:

­ some organisms don’t get Carbon 14 from food chain

­ ex: the Zombie Clams

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