Geology Exam 2 2

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External Processes: -occur at/near earth's surface
-powered by the sun
-transform rock into sediment

1)WEATHERING

2)MASS WASTING

3)EROSION
Weathering: physical brekadown & chemical alteration of rock at/near Earth's surface
Mass Wasting: transfer of rock/soil downslope due to gravity
Erosion: physical removal of material by mobile agents (water, wind, ice)
Internal Processes: -Earth's surface built up
-get energy from earth's interior
-mountain building/volcanic activity
2 Types of Weathering: 1)Mechanical Weathering

2)Chemical Weathering
Mechanical Weathering: breaking of rocks into smaller peices (due to physical forces)
*doesn't change rock's mineral comp*

(many small pieces form from a single large one)
Chemical Weathering: chemical transformation of rock into 1 or more different compounds

**most significant result = decomposition of unstable minerals AND retention/generation of stable materials
--->account for predominance of certain minerals in surface soil
4 Types of Mechanical Weathering: 1)Frost Wedging
2)Unloading
3)Thermal Expansion
4)Biological Activity
Thermal Expansion: alternate expansion & contraction due to heating & cooling

-heating rock = expansion
-cooling rock = contraction
====swelling shrinking of minerals at different rates
Biological Activity: disintigration resulting from plants/animals

-burrowing
-plant roots
Major processes of Chemical Weathering: 1) Dissolution
2) Oxydation
3) Hydrolysis
Dissolution: -minerals dissolve in water
--aided by acid in water (H+)
--acid increases water's corrosive force

*large quantities of limestone over thousands of years carried away underground = caverns
*dissolved ions in water = hard water [ions react w/soap]

***most water-soluble mineral = HALITE
-->H20 molecules are polar
--->dissasociates sodium & chloride ions in halite
Oxidation: -Chemical reaction where compound loses electrons
-important for breaking down mafic minerals

-rusting (causes iron oxide, Hematite; & rust limonite)
-oxidized if it lost electrons to oxygen
-addition of water increases speed of oxydation
**Oxidation only occurs after iron freed by HYDROLYSIS
Hydrolysis: reaction of any substance w/ H20

-can take place in pure H20 if water molecule dissociates into H+ & OH-
---> the H+ ions attack & replace other positive ions in crystalline structure
-----> orderly arrangement of atoms destroyed --> mineral decomposes

-H20 usually contains other substances that contribute H+ ions & accelerate hydrolysis
*carbon dioxide (CO2) acquired from atmosphere in rainwater & decaying organic matter

-silicates primarily decomposed by hydrolysis
____ causes rocks to increase in surface area and thus aids _____: Mechanical Weathering
breaks rocks into smaller & smaller pieces thus Increasing Surface Area and aiding
Chemical Weathering
Factors affecting weathering (other than surface area / mechanical weathering) ---LIST---: 1)ROCK CHARACTERISTICS

2)CLIMATE
Acid Mine Drainage: type of oxidation reaction:
-sulfide minerals decompose like:
-PYRITE (in coal deposits [old mines])
-moist/rain = weathering of pyrite
---> yields sulfuric acid & iron oxide
Chemical Weathering causes Physical Changes: -Spheroidal weathering
-in forming spheroidal boulders shells can seperate from main body & break off
--->chemical weathering can penetrate deeper into boulder
(bc minmerals weeather to clay, acquire H20 & increase in size--->outward force making layers fall off)
Spheroidal Weathering: The corners of rocks are attacked more than faces / edges
bc of greater surface area : volume ratio
--->Take on spherical shape

(ex. angular rock fragments attacked by water flowing through joints)
Rock Characteristics affecting Weathering: -PHYSICAL CHARACTERISTICS:
-joints/cracks allow H2O to penetrate rock
-MINERAL COMP:
-marble / limestone dissolve easily in weak acidic solutions (granite doesn't)
-**Silicate minerals weather in REVERSE order of their crystallization**
-strength of silicon-oxygen bonds = stong

-temp & moisture most crucial factors (ex..freeze/thaw)
-chemical weathering more effecting in WARM WET climates
(lush veg=more decayed organic matter=more H+=more acid=more weathering)
Climate affecting Weathering: -temp & moisture most crucial factors (ex..freeze/thaw)
-chemical weathering more effective in WARM WET climates
(lush veg=more decayed organic matter=more H+=more acid=more weathering)

-polar regions-->chemical weathering ineffective [cold temp keep moisture locked as ice]
-arid regions = not enough moisture for chem reactions
Differential Weathering: when rocks don't weather uniformly (at same rate)

Factors Influencing Diff. Rates:
1)Variation in Comp
2)Joint Spacing & # of Joints
SOIL: combination of (support plant growth):
-Mineral Matter (45%) [decomposed rock]
-Organic Matter (5%) [humus-decayed plant/animal matter]
-Water (25%) [in pore spaces]
-Air (25%) [in pore spaces]

--->the portion of the Regolith [weathered rocks/minerals] that supports plants

*organic matter/humus increases ability to retain H2O
Factors Controlling Soil Formation: 1) Parent Material
2) Time
3) Climate
4) Plants/Animals
5) Slope (topography)
Parent Material influencing Soil Formation: -parent's comp affects soil types
-affects rate of weathering & rate of soil formation
-the chem makeup of parent material affects soil's fertility

-when parent material is unconsolidated deposits soil development progresses faster than when parent material is bedrock
Time influencing Soil Formation: Soils get better developed w/more Time

-weathering for short time --> parent material determines soil characteristics
-weathering for long time --> less influence of parent material more influence by climate

*the longer soil's been forming the thicker it is & the less it resembles the parent material
Climate influencing Soil Formation: Biggest Control on Soil Formation
-key factors = Temp & Precipitation
(they determine whether chemical or mechanical weathering will predominate)
-influence rate & depth of weathering

*hot/wet climate = thick layer of chemically weathered soil
in same amt of time
cold/dry climate = thin mechanically weathered soil
Plants & Animals influencing Soil Formation: influence physical & chemical properties of soil
-supply organic matter to soil (primary source = plants)

-decomposing organic matter supplies nutrients
-more organic matter = higher soil fertility
-decaying organic = organic acids = speed up weathering
-organic matter = high H2O holding ability
Slope (Topography) influencing Soil Formation: Steep Slopes =
-small quantity of H2O retention
-accelerated erosion
-->soils thin / sometimes nonexistent

poorly drained/water-logged soil:
-thick/dark
-dark due to high amt of organic matter (saturation slows decay)

*optimum terrain for soil formation is flat to wavy surface (good drainage, minimal erosion, sufficient H2O infiltration)

-slope orientation (face direction) influences.. [UV rays etc.]
Soil Profile: a vettical section through all soil horizons

(soil processes operate from the surface downward)

O, A, E, B, & C
horizons
Soil Horizons: Vertical differences divided into zones

(more pronounced differences as time passes)
Soil Horizons Listed: (topsoil)
-O HORIZON
-A HORIZON
(leaching zone)
-E HORIZON
(subsoil)
-B HORIZON
(....)
-C HORIZON
O HORIZON & A HORIZON [TOPSOIL]: O HORIZON:
(ORGANIC MATTER)
-mainly mineral matter
-top = plant litter
-bottom = humus
-contribute to O2, CO2

A HORIZON:
(ORGANIC & MINERAL MATTER)
-high biological activity
E HORIZON: -little organic matter
-finer particles washed away (eluviation)
-soluble materials carried into deeper zones(LEACHING)
B HORIZON [SUBSOIL]: -ZONE OF ACCUMULATION
--material removed from E deposited here in B
--accumulation of fine clay increases H2O retention
C HORIZON: -PARTLY ALTERED PARENT MATERIAL
-undergoing changes but not yet "soil", still "regolith"
Solum / "true soil": O, A, E, & B
Horizons
Soil Types depend primarily on _______: CLIMATE
3 Generic Soil Types: 1) Pedalfer

2) Pedocal

3)Laterite
PEDALFER soil type: -accumulation of iron oxides & Al-rich clays in B HORIZON
-best developed under forest landscapes
PEDOCAL soil type: -high accumulation of calcium carbonate
-dry grasslands
-brush vegetation
---[DESERTS]
LATERITE soil type: -intense chemical weathering
-hot/wet tropical climates
Soil Erosion Depends On: -soil characteristics
-climate
-slope
-vegetation type

(soil erosion is the recycling of earth's materials)

-farmers level feilds to slow soil erosion
-erosion can be greater than formation at times
sedimentary rocks result from: -mechanical & chemical weathering yield sediment
-sediment is deposited
-accumulates
-compacted
-cemented together by mineral matter (in spaces between sediment particles)
make up __ % of earth's upper crust: 5 %
Sediments indicate: the past environment they were deposited in
-clues to how they were transported
-fossils
Sedimentary rocks important for Economic Reasons: COAL - provides energy

sed. rocks = sources of PETROLEUM & NATURAL GAS

sources of IRON, ALUMINUM, MANGANESE, URANDIUM

& used to read earth's history
Diagesis: all of the chemical, physical, & biological changes that take place after sediments deposited

(during & after lithification)

*promoted by burial bc higher temps & pressure (beyond upper crust = metamorphism)
Recrystallization (example of diagenetic change): development of stable minerals from less stable ones
Lithification (included in diagenesis): loose sediment transformed to solid rock by compaction & cementation
Compaction (physical diagenetic change): accumulated sediment compresses deeper sediments by weight of overlying material

-deeper sediment buried = more its compacted = firmer = reduction in pore space = H2O driven out

*most significant in fine-grained sediments (bc coarse sediments like sand less compressable)
Cementation (chemical diagenetic change): precipitation of minerals amoung sediment grains

-cementing materials carried by H2O through pore spaces
-cement precipitates onto sediment grains, fills pore spaces, joins particles
Natural Cements (3): calcite
silica (hardest- produces hardest sediments)
iron oxide (produces orange-dark red color in rocks)
Detrital rocks: transported sediment as solid particles

(transported from mechanical and chemical weathering)

*distinguished by particle size*
Chemical Rocks: precipitated [seperation from solution as a solid] material that was once in a solution

(chemical weathering by inorganic or organic processes)
constituents of detrital rocks: 1. CLAY MINERALS (most abundant product of chemically weathered silicate minerals)
2. QUARTZ(durable, resistent to change)
3. FELDSPARS (indicates erosion & deposition fast enough to presevesthese primary minerals)
4. MICAS (indicates erosion & deposition fast enough to presevesthese primary minerals)
types of detrital rocks: Shale
Sandstone
Conglomerate/Breccia
SHALE detrital rock: sediment = mud
< 1/16 mm
particles = silt/clay

-most commmon sedimentary rock
-gradual settling -- non-turbulant currents
-lakes, lagoons
-much deposited only after individual particles coalesce to form larger aggregates

-silt & clay accumulate to form thin layers (LAMINAE)
---->disorderly arrangement
---> a lot of pore space filled w/ H2O
-->layering on top squeezes out H2O
--->smaller pore spaces = no circulating solutions of cementing material
====>WEAK, Poorly Cemented, not well lithified.

*prevents groundwater from continuning downward & petroleum and gas from going upward

** ability to split into thin layers along closely spaced planes (FISSILITY)

-crumbles easily
SANDSTONE detrital rock: sediment = sand
1/16 - 2 mm
particles = sand

-form in many diff enviros
-sorting & comp of grains show rock's history
-predominant mineral = QUARTZ

-deduced by SORTING, ROUNDNESS, & MINERAL COMP.
CONGLOMERATE / BRECCIA detrital rock: sediment = gravel
> 2 mm
particles = boulder, cobble, pebble, granule

-particles large enough to be identified & valuable in identifying sources of sediments
-poorly sorted bc spaces between gravel particles contains sand or mud
-gravel usually indicates steep slopes or turbulent currents

BRECCIA = angular (didn't travel far)
CONGLOMERATE = rounded
sandstone origin deduced by SORTING: SORTING = degree of similarity of particle size

well sorted - all grains ~ same size
poorly sorted - rock contains mixed large & small particles

windblown sand = better sorted than wave tranported sand

tranported for short time = poorly sorted
sandstone origin deduced by ROUNDNESS: more rounded = airborne or waterborne transportation & lots of transport

more angular = transported short distance before deposition, glacier transport common
sandstone origin deduced by MINERAL COMP.: substantial weathering & long transport = detroys weaker/less stable minerals (feldspars & ferromagnesians)

quartz durable = usually survives transport

(*well-sorted quartz rich rounded grains = a lot of transport
*feldspar & angular grains of ferromagnesian minerals = little chemical weathering & transport*)
Chemical Sedimentary Rocks LISTED: Limestone
Dolostone
Chert
Evaporites
Coal
LIMESTONE chemical sedimentary rock: -most abundant chemical rock
-made of mineral calcite
-produced under variety of conditions - many types exist

BIOCHEMICAL LIMESTONES:
1)Coral Reefs
2)Coquina
3)Chalk

INORGANIC LIMESTONES
1)Travertine
2)Oolitic Limestone
--Coral Reef Limestone: the coral organism secretes calcite-rich external skeleton

reefs = coral colonies
(biochemical)
--Coquina Limestone & --Chalk Limestone: COQUINA:
coarse rock composed of poorly cemented shells/shell fragments (biochemical)

CHALK:
soft, porous rock made of hard parts of microscopic marine organisms (Biochemical)
--Travertine Limestone: TRAVERTINE:
-seen in caves
-water droplets exposed to air in cave some of carbon dioxide escapes causing calcium carbonate to precipitate
(InOrganic [calcium carbonate concentration increases to precipitation point])
--Oolitic Limestone: -composed of small round grains [ooids]
-ooids form in shallow marine waters as "seed particles" (shell fragments) & rolled in warm current
--->water is saturated in calcium carbonate
------>ooids become coated with precipitate
(InOrganic)
DOLOSTONE chemical sedimentary rock: -typically formed secondarily from limestone
-common in ancient rocks--rare today
-most originates when magnesium replaces calcium in limestone
CHERT chemical sedimentary rock: -made of microcrystalline quartz
-usually deposited as siliceous ooze in deep oceans
-originated largely from biochemical sediment
-diatom organisms produce glasslike silica skeletons
-conchoidal fracture

*flint (dark bc of organic matter)
*Jasper (red bc of iron oxide)
*Agate (banded form)
EVAPORITES chemical sedimentary rock: -evaporations deposites chemical precipitates
-halite mineral produces ROCK SALT
-gypsum deposited produces ROCK GYPSUM (plaster)

-less soluble minerals precipitate first, more soluble minerals precipitate later as salinity increases

-salt flats form when dissolved materials are precipitated as white crust of ground
COAL chemical sedimentary rock: -UNIQUE: composed of organic material

Stages:
1)Plant Material
2)Peat
3)Lignite
4)Bituminous
STAGES IN COAL FORMATION 1)Peat 2)Lignite 3)Bituminous 4)Anthracite: 1)PEAT:
-enviros such as swamps are O2 deficient so plant material isn't completely decayed
-the partially decomposed plants = PEAT layer
--plant structures still easily recognizable

2)LIGNITE
-with shallow burial peat changes to lignite
---soft brown coal
(sedimentary rock)

3)BITUMINOUS
-deeper burial - water pressed out - proportion of fixed carbon (combustable material) increases
-higher energy coal
-used to generate power
(sedimentary rock)

4)ANTHRACITE
-sediment layers subjected to folding & deformation
-metamorphosized
-more water pressed out & higher concentration of fixed carbon
---Yields ANTHRACITE
--hard shiny clack metamorphic rock
-more difficult/expensive to extract
-high energy
How are Sedimentary Rocks Classified?: 1)Detrital
(subdivided by particle size)
-all have CLASTIC texture
["broken" - fragments of particles cemented but pores not completely filled]

2)Chemical
(subdivided by mineral comp)
-some CLASTIC {coquina & some oolitic limestone}
-some NON-CLASTIC [crystalline texture - minerals form pattern of interlocking crystals] {evaporites}
"sedimentary environment" define & (3)types: geographic setting where sediment accumulates

-determines nature of sediment that accumulates (grain size & shape)

1)Continental
2)Marine
3)Transitional
Continental sedimentary environment: -dominated by erosion & deposition associated w/streams
-glacial [poorly sorted]
-wind (resulting deposits = "EOLIAN"[well sorted] )
Marine sedimentary environment: 1)SHALLOW(<200 M)
-receives larrge quantities of land derived sediment due to erosion of continents
-coral reefs

2)DEEP(>200M)
-small grains accumulate slowly
Transitional sedimentary environments: the shoreline

-beaches (sand/gravel deposites)
-TIDAL FLATS ()
-LAGOONS
-DELTAS
Sedimentary Structures: provide additional info about earth history

STRATA:
(beds) most characteristic of sedimentary rocks

BEDDING PLANES:
flat surfaces along which rocks tend to sparate/break (change in grain size or comp of sediment deposited can create these planes)
*generally represent end of one episode of sedimentation & beginning of another*

CROSS BEDDING: characteristic of sand dunes, river deltas (NOT horizontal)

GRADED BEDS:
waning flow[stream energy gradually decreases] (particles w/i sedimentary layer change from coarse at bottom to fine at top)

RIPPLE MARKS:
small waves of sand developed on surface of sediment layer by moving water or air
-low energy enviro
-right angles to directions of motion
-determine direction of movement of ancient winds/currents
-(oscillation ripple marks = back&forth movement & symmetrical form)

MUD CRACKS:
drying of mud-filled pools
-sediment was alternately wet/dry

FOSSILS:
traces of past life preserved in rock
*aid interpretation of past
*time indicators
*allow for correlation of rocks from different places
"metamorphism": the transformation of one rock type into another

changes in the minerology, texture and chemical composition

progresses from low grades (slight changes [shale->slate]) to high grades (substantial changes [parent rock can't be determined-fossils/bedding planes obliterated])

rocks remain solid during metamorphism (if melts completely = igneous activity)

Causes?
1) HEAT
2) PRESSURE
Agents of Metamorphism: 1)HEat
2)Pressure
3)Chemically Active Fluids

all 3 occur at the smae time during metamorphism but degree of each differs
HEAT agent of metamorphism: -most important agent
-drives recrystallization
[fine grained particles coalesce into large ones]
-create new stable minerals
[rock raised above temperature that minerals are no longer stable --> component ions arrange themselves into structure more stable inthe new high-energy enviro]

*pressure & temp work independently of eachother
PRESSURE (STRESS) agent of metamorphism: -increases w/depth
-"Confining Pressure"- buried rocks--applied equally in all directions [spaces between minerals close-compact rock-higher density]
-"Directed Pressure"-convergetn plate boundaries -unequal in diff directions - "differential stress"
-->rock is folded or flattened
Main factor affecting Metamorphism?: PARENT ROCK
-meta rocks usually have same chemical comp as parent
-different minerals but made of same stuff
-parent rock determines the degree each metamorphic agent will cause change
3 Types of Metamorphic Settings: 1)Contact Metamorphism
2)Hydrothermal Metamorphism
3)Regional Metamorphism
CONTACT METAMORPHISM metamorphic setting: *frome a rise in temp within a host rock*
-rock is intruded by magma body
-change driven by rise in temp within the host rock surrounding an igneous intrusion
-"aureole" (zone of alteration forms surrounding emplaced magma body) (dikes/sills/magma bodies)
HYDROTHERMAL METAMORPHISM metamorphic setting: *chemical alterations from hot, ion-rich H2O*
--circulates through rock fractures
-igneous activity provides heat to drive reactions
***occurs simultaneously w/contact metamorphism***
-most along mid-ocean ridge
REGIONAL METAMORPHISM metamorphic setting: *occurs in cores of mountain belts*makes great volumes of meta rock*
-most occurs along convergent plate boundaries
---compressional stresses deform plate edge
---alps, himalayas, appalachian mntn belts
linear relationship in core of subduction zone: --high P, low T zones near trench

--high T, low P zones in arc of igneous activity
Index Minerals: certain minerals that indicate the metamorphic envro in which they formed
Metamorphic Grade: group of minerals formed in particular P-T enviro

Zeolite (very low T, very low P {<200C})

GREENSCHIST (low T, low P; {200-450C, 10-15km})

BLUESCHIST (low T, high P; SUBDUCTION ZONES)

AMPHIBOLITE (high T, high P; {450-650C, 15-20km})

GRANULITE (very high T, very high P; {>700C, >25km}
migmatites: banded rock of light egneous components & dar unmelted meta material

(don't belong in any rock category)
MetamorphiC Texture: size shape & arrangement of mineral grains w/i a rock
Foliation: planar (nearly flat) arrangement of mineral grains w/i a rock

--when rock exhibits preferred orientation of its minerals

-driven by compressional stresses that shorten rock units
--->causes mineral grains to develop parallel allignments
Foliation can form by:: 1) rotation of platy or extended mineral grains into new orientation

2)recrystallization of inerals to form new grains growing in direction of preffered orientation

3)changing the shape of equidimensional grains into elongated shapes-->which are alligned in their preffered origin
Non-Foliated: develop in enviros where deformation is minimal and parent rocks are composed to equidimensional crystals
[like quartz / calcite]
FOLIATED ROCKS list: (shallowest)
Slate
Phyllite
Schist
Gneiss
(deepest)
SLATE foliated rock: -very fine-grained
-excellent cleavage (flat slabs)
-made by low grade meta of shale

*expensive roofs*
PHYLLITE foliated rock: -meta grade between slate & schist
-made of small platy minerals (larger than slate but still not visible)
-glossy sheen
-cleavage
-comp of muscovite & chlorite
SCHIST foliated rock: -medium-->coarse grained
-comprised of platy minerals (micas)
-"schist" describes texture
-wide variety of chemical comp
(so mineral names used - mica schist)
GNEISS foliated rock: -medium-->coarse grained
-banded
-high grade meta (during this the light & dark components seperate)
-composed of light feldspar layers & dark mafic bands
NON- FOLIATED ROCKS list: Marble
Quartzite
MARBLE non-foliated rock: -coarse, crystalline
-parent rock = limestone
-comp of calcite crystals
-fabric = random or oriented
-soft, easy to cut /shape
-statue of david
-attacked by acid rain (due to calcium carbonate comp)
QUARTZITE non-foliated rock: -parent rock = quartz rich sandstone
-quartz grains are fused together
--->recrystallization so complete that when broken will split thru quartz grains not along boundaries
-forms in intermediate T / P conditions
Relative v Absolute Dating: Relative: rocks and events in proper sequence

Absolute: define actual age of even with numerical dates
Law of Superposition: -Steno (1669
-in undeformed sequence of sedimentary rocks oldest at bottom; youngest at top
Principle of Original Horizontality: layers of sediment originally deposited horizontally
(flat strata haven't been disturbed)
Principle of cross-cutting: younger features cut across old ones
inclusions: fragments of a rock enclosed w/i another
-->the rock mass next to the one including the inclusion was there first (to provide rock fragments)
Unconformities (3 types): a long period during deposition ceased, erosion removed previously formed rocks, & deposition resumed

-helps us identify what time intervals aren't reped by strata & are missing from geologic record

1-angular unconformity
2-disconformity
3-nonconformity

(conformable = w/o interruption = no where)
Angular unconformity: tilted rocks are overlain by flat-lying rocks

-during a pause in deposition, deformation (folding/tilting) then erosion occurred
Disconformity (unconformity): strata on either side of unconformity are parallel (but time is lost)
Nonconformity (unconformity): sedimentary rocks deposited above meta & igneous rocks

-break seperates old meta or igneous from new sedimentary strata

--must be a period of uplift & erosion
"Correlation" (of rock layers): matching strata of similar ages in different regions

-relies on fossils
principle of fossil succession: fossil organisms succeed one another in recognizable order (any time period can be defined by the fossils in it)

Index Fossils = widespread geographically limited to short time span ==>matches rocks of same age

(shows ancient shorelines)
general types of fossils: -molds (something buried then dissolved)
-casts (mold filled with mineral matter)
-tracks
-burrows
-coprolites (fossil dun and stomach contents)
-gastroliths (polished stomach stones used in grinding of food)
conditions favoring preservation: -rapid burial (not eaten/decomposed)
-hard parts
Geologic Time Scale: divides geologic history into units
(originally created using relative dating)
*divisions based on fossils

(greatest
-Eon
-Era
-Period
-Epoch
(shortest)
Eon: (greatest)

1)Panerozoic

2)Precambrian
--a-proterozoic
--b-archean
--c-hadean
Eras of Phanerozoic: ("visible life"-most recent eon-abundant fossils showing evolutionary trends)

1)cenozoic (recent life)
2)mesozoic (middle life)
3)paleozoic (ancient life)
Precambrian "Eon" (General): -4 billion years prior to cambrian
-not known in detail (not divided into small time units)
-immense space of time
Eras of Phanerozoic divided into Periods: 1)Cenozoic
--a-Quaternary
--b-Tertiary
2)Mesozoic
--a-Cretaceous
--b-Jurassic
--c-Triassic
3)Paleozoic
--a-Permian
--b-Carboniferous
--c-Devonian
--d-Silurian
--e-Ordovician
--f-Cambrian
Radioactivity: used to numerically date rocks

-spontaneous changes/ decay in structure of atomic nuclei (of isotopes)

-nuclei are unstable bc forces binding protons/nuetrons not strong enough
Atomic # v Mass #: Atomic #: number of protons
(atoms of same element always same proton #)

Mass #: nuetrons + protons
(variants = isotopes of the element)
Types of Radioactive Decay: 1)Alpha Emission
2)Beta Emission
3)Electron Capture
Alpha Emission: emission of 2 protons & 2 nuetrons (an alpha particle)

*mass # reduced by 4, atomic # reduced by 2*
Beta Emission: electon (beta particle) ejected from nucleus

*bc electron came from neutron the nucleus contains one more proton
-->atomic # increases by 1
Electron Capture: electron is captured by nucleus
-electron combines w/proton to form neutron

*nucles contains one less proton-->atomic number decreases by 1 (mass # remains)*
Parent (in radioactive dating): an unstable radioactive isotope
Daughter product (in radioactive dating): isotopes resulting from the decay of parent
Half Life: time required for 1/2 of parent isotope to decay

parent:daughter ratio=
(1:1)= 1 half life
(1:3)= 2 half lives
(1:7)= 3 half lives
Radiocarbon Dating (dating w/ Carbon-14): -to date RECENT events
-half life = 5730 yrs
-carbon-14 produced in upper atmosphere
-
Radiometric Dating: the calculating of rock/mineral ages that contain particular radioactive isotopes

IMPORTANCE:
-calibration of geologic time scale
-determines geologic history
-confirms that geologic time is immense
procedure for actually "dating" a rock: 1)collect sample
2)process for minerals
[crush, sieve, seperate magnetically or w/heavy liquids]
3)measure parent/daughter ratio of mineral separates w/mass spectrometer

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