GEOL162-GeologicTime

7/25/2019 GEOL162-GeologicTime

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Geological Time - really, really, really long!

Motion pictures are generally projected at 32 framesper second. Therefore, each frame (image) is on the

screen for only split second- let each frame represent100 years.tart mo!ie at present and go "ac# in time.

The $eclaration of %ndependence &ould sho& up 1'1of a second into the mo!ie.The hristian era (*-+$ "oundary) &ould "e 3' ofa second into the mo!ie.The most recent %ce +ge &ould "e seconds into it.The mo!ie &ould run a"out hours "efore &e got to

the end of the Mesooic era (e/tinction of thedinosaurs).ed ha!e to &atch the mo!ie for a"out 2 days tosee the "eginning of the aleooic era (macroscopiclife).The &hole mo!ie (to the "eginning of geologic time on


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QuickTime and aTIFF (Uncompressed) decompressor

are needed to see this picture.


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> 5elati!e6 lacing e!ents in ase7uence "ased on their positionsin the geologic record.

> hronologic

sample.

T&o &ays to relate time in geology6> 5elati!e6 lacing e!ents in ase7uence "ased on their positions

in the geologic record.

> hronologic 6 lacing a specific

num"er of years on an e!ent or roc#sample.

8eologic Time


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8eologic Time cale

a com"ination of the t&o types of agedeterminations

> a relati!ese7uence of lithologic units-esta"lished using logical principles

> measured against a frame&or# of

chronologicdates.


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8eologic Time and the 9geologic column9 Developed using logical rules to establish relative

sequences of events

----

rened

-

-

8eologic Time and the 9geologic column9 Developed using logical rules to establishrelative sequences of events

- superposition- cross-cutting relationships- original hori.ontality- lateral continuity

Added to as new information is obtained anddata is rened

- :se of fossils for correlation and age determination

Numerical Dates attached to strata after the

development of Radiometric techniques-

till "eing refined as more information"ecomes a!aila"le


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The 8eologic Time cale (162)


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The 8eologic Time cale (262)


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5elati!e $ating Methods

determines the relati!e se7uence of e!ents.> &hich came first, &hich came last.> no numeric age assigned

5elati!e age principles6> uperposition ; >ateral continuity ;ross-cutting 5elationships> %nclusions ;?ossil succession.

Those in yellow are most useful


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>a& of uperposition%n undistur"ed strata, the layer on the "ottom is%n undistur"ed strata, the layer on the "ottom isoldest, those a"o!e are younger.


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ateral ontinuityediment layers e/tend laterally in all

direction until they thin @ pinch out astheymeet the edge of the depositional"asin.


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included description and use of

harles >yell

A

-

;principles of cross-cutting relationships

;principles of inclusions

A relati!e time tools

harles >yell

A 1st rinciples of 8eology te/t

-

;principles of cross-cutting relationships

;principles of inclusions

A relati!e time tools


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ross-cutting 5elationships

That which cuts through is younger than theObject that is cut

di#e cuts through

granite is cut


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5elati!e +ges of >a!a ?lo&s and ills


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rinciple of %nclusionsInclusions (one rock type contained in another rock type) areolder thanthe rock they are embedded in. That is the youngerrock contains the inclusions


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rinciple of %nclusions

? l'?l l i


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?aunal'?loral uccession ?ossil assem"lages (groupings of fossils)

succeed one another through time.

l ti


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--

-

-

A orrelation-relating rocks in one location to those in

another using relati!e age stratigraphic

principles-"uperposition-

#ateral $ontinuity-

%aunal "uccession

- $ross-cutting


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Unconformitiessurfaces

represent a long time.a time when rocks were not

deposited or

a time when rocks were

erodedHiatus

the gap in time represented

in the rocks by an uncon-

formity

3 kinds

Angular Unconformity

Nonconformity

Disconformity

$i f i i


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$isconformities+ surface of erosion or non-deposition "et&eenarallel sedimentary roc# "edsof differing ages.

+ l : f i i+ l : f iti


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+ngular :nconformities+ngular :nconformities&nangular unconformity is an erosional sur'ace on tiltedor 'olded strata o!er which younger strata ha!e been deposited.

B f iti


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Bonconformities&nonconformity is an erosional sur'ace on igneous ormetamorphic rocks which are o!erlain by sedimentary rocks.

i i


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Breakout in to groups and discuss the sequence

observed here


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+ge stimates of arthounting lifetimes in the *i"le

omparing cooling rates of iron pellets.

$etermine sedimentation rates @ compare

stimate age "ased on salinity of the ocean.

all age estimates &ere off "y "illions of years some &ere more off than others4


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>

+

Absolute Dating Methods

adioacti!e Decay se"uencesacts as an atomic clock

we see the clock at the end of its cycle

analogous to starting a stopwatchallows assignment of numerical dates to

rocks.>

+

decay# intoadioacti!e isotopes change $daughter isotopes at known rates.

rates vary with the isotope

e.g., U , K , C, etc.

235 40 14


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$ecayunsta"le nuclei in parent isotope emitssu"atomic particles and transform intoanother isotopic element (daughter).

does so at a #no&n rate, measured in thela"

=alf-lifeThe amount of time needed for one-half of aradioacti!e parent to decay into daughterisotope.

+ssumptionsC-you "et

ross-chec#s ensure !alidity of method.


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Rate of Decay

t0

t1

t3

All atoms are parent isotope or some

known ratio of parent to daughter

1 half-life period has elapsed, half of thematerial has changed to a daughter

isotope (6 parent: 6 daughter)

t22 half-lives elapsed, half of the parentremaining is transformed into a daughter

isotope (3 parent: 9 daughter)

3 half-lives elapsed, half of the parentremaining is transformed into a daughterisotope (1.5 parent: 10.5 daughter)

We would see the rock at this point.

5adioacti!e %sotopes5adioacti!e %sotopes


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5adioacti!e %sotopes

analogous to sand in an hour glass-&e measure ho& much sand there is

> represents themass of elements-&e measure the ratio of sand in the "ottom to sand in the top-at the end (present)

> daughter (") and parent (t)-&e #no& at &hat rate the sand falls into the "ottom

> the half life of the radioacti!e element-ho& long &ould it ta#e to get the amount sand in the o"ser!ed

ratio starting &ith all of it in the topC

5adioacti!e %sotopes

analogous to sand in an hour glass-&e measure ho& much sand there is

> represents themass of elements-&e measure the ratio of sand in the "ottom to sand in the top- at the end (present)

> daughter (") and parent (t)-&e #no& at &hat rate the sand falls into the "ottom

> the half life of the radioacti!e element- ho& long &ould it ta#e to get the amount sand in the o"ser!ed

ratio starting &ith all of it in the topC

D0

100

2D13

time-----------;

arent$aughterarent$aughter

%

pa

ren

tr em

ain

ing

Fi Rdi ti I t PiFiveRadioactiveIsotopePairs


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Five Radioactive Isotope PairsFive Radioactive Isotope Pairs

Half-Life

Effective Minerals and Isotopes of Parent

Dating RangeRocks That Can

Parent Daughter(Years)

Be Dated

Uranium 238 Lead 206 4.5 billion 10 million to Zircon

4.6 billion UraniniteUranium 235 Lead 207 704 million

Thorium 232 Lead 208 14 billion 48.8 billion

Rubidium 87 Strontium 87 4.6 billion 10 million to

Muscovite

Biotite

Potassium feldspar

Whole metamorphic

or igneous rock

Potassium 40Argon 40 1.3 billion 100,000 to Glauconite

4.6 billion Muscovite

Biotite Hornblende

Whole volcanic rock

(Years)

4.6 billion


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5adiocar"on and Tree-5ing $ating Methodsar"on-1 dating is "ased on the

ratio of -1 to -12sample.> Ealid only for samples less than 0,000years old.

> >i!ing things ta#e in "oth isotopes ofcar"on.

> hen the organism dies, the 9cloc#9 starts.

ar"on-1 dating is "ased on the

ratio of -1 to -12 in an organicsample.> Ealid only for samples less than 0,000years old.

> >i!ing things ta#e in "oth isotopes ofcar"on.

> hen the organism dies, the 9cloc#9 starts.

Method can "e !alidated "y cross-chec#ing &ith treerings

C b 14C l


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Carbon 14 Cycle

5ecogni.ing atterns of change


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5ecogni.ing atterns of change

althers >a& The !ertical se7uence is repeated "y the hori.ontal

se7uence

- &al#ing from + to * to to the oast you &ould encounter theroc#s that &ould "e encountered "y drilling a core into the

earth at any point (+, *, or )

?acies $iagram


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?acies $iagram distri"ution of lithofacies (roc#-types)- these are associated &ith their respecti!e


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ustasy, relati!e sea-le!el, and relati!e position

of lithofacies ustasyF changes in !olume of &ater in ocean

lithofacies depend on- sea-le!el

- land le!el

- geometry of coast

- sediment supply

Eail ur!e an attempt at glo"al

correlation oflithologies- for "etter production

- of petroleum resources


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5oc# designations Rock units called Lithostratigraphic units

- descri"ed in terms of 8roup, ?ormation, @ Mem"er

> each term has specific meanings in geological parlance Formation

- a mappa"le lithostratigraphic unit> has a location for identifying the type-section

> has a roc# designation descri"ing the lithology- sometimes not all the same lithology

> in &hich case the term 9?ormation9 ta#es the place of lithologic

type

Groups are composed of several formations Members are distinctive units within a formatio

-group is largest and contains formations and mem"ers

- formations are ne/t and contain mem"ers

5oc# designations Rock units called Lithostratigraphic units

- descri"ed in terms of 8roup, ?ormation, @ Mem"er

> each term has specific meanings in geological parlance Formation

- a mappa"le lithostratigraphic unit> has a location for identifying the type-section

> has a roc# designation descri"ing the lithology- sometimes not all the same lithology

> in &hich case the term 9?ormation9 ta#es the place of lithologic

type

Groups are composed of several formations Members are distinctive units within a formatio

-group is largest and contains formations and mem"ers

- formations are ne/t and contain mem"ers


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%undamental lithological units

%ormation- a rock layer with distincti!echaracteristics that is mappable o!er a large are attypical map scales

*+,// or more commonly *+0///

%ormations ha!e 1embers

smaller layers that are uni2ue that are not mappableo!er larger areas and won3t show up at typical map scales

4roups ha!e 'ormations5 'ormations ha!e members

Documents

GEOL162-GeologicTime