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Final

EESA06H3 Final: EESA06-Finals-Notes


Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles
Study Guide
Final

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EESA06&Finals&Notes&
&
Lec&08&
!
deep!time/!geologic!time-&4.5&billion&years&ago&
In&the&last&20&years&that&we’ve&developed&relatively&inexpensive&methods&
that&can&be&readily&duplicated&around&the&world&for&age&dating&rocks.&
absolute!age=&real&age&&
Relative!age!dating&-&“Well&based&on&mapping&in&the&field,&mapping&of&rock&layers,&
this&rock&layer&is&older&than&this&other&rock&layer.”&
Strata-&layers&of&rock&
Stratigraphy-&&the&sub-discipline&of&geology&which&is&concerned&with&age&of&rocks.&&
- study&of&how&all&those&rocks&are&arranged&in&time&as&revealed&by&strata.&
Accommodation-&in&order&to&get&rocks&preserved,&areas&of&the&crust&must&subside&
(Ocean&basins,&subduction&zones,&other&types&of&basins)&that&way&it&usually&floods&
with&water&and&accumulate&sediment.&&
Basins-&the&crust&to&be&sinking&over&broad&areas&or&subsidence.&&
Uplift-&opposite&of&subsidence,&results&in&non-accommodationà&&erosion&and&
removal&of&sediment&and&rock,&tectonics&
&Ex:&Grand&Canyon&area&must&subside&in&the&past&in&order&to&accommodate&its&
layers.&&
- Bottom=&Oldest&layer&&
- Top=&youngest&layers&
succession-&&is&where&those&layers&sit&on&each&other&without&any&major&breaks.&It’s&
almost&like&a&continuous&record&of&environments&
&
unconformable&succession&where&there&are&major&time&breaks&within&the&
succession.&
&
“More!gaps!than!record”-&last&4.5&billion&years&of&earth&history&there’s&more&time&
which&is&unrecorded&by&rocks&than&there&is&that&is&actually&recorded.&Rock&record&is&
incomplete.&That&there&are&major&gaps.&Because&a&lot&of&rocks,&a&lot&of&sediments&
record&distinct&events&separated&by&long&periods&where&nothing&happens.&
&
Fossil-&&fossilized,&lithified&remains&of&an&organism.&Organisms&evolve&through&
time.&So&if&we&look&at&any&one&fossil&type&and&compare&that&with&other&types&
elsewhere,&we&can&usually&put&them&in&some&sort&of&relative&age&position.&

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&
formal!succession-&the&succession&of&fossil&types&that&record&evolution&through&
time.&&“Well&this&fossil&has&more&primitive&characteristics&than&this&one,&so&it’s&
older.”&
&
Index!fossils-!organisms&that&evolved&very&quickly&
Grand!Canyon!!
- Everything&is&flat&line.&That’s&not&the&case&in&many&parts&of&the&world&where&
the&rocks&have&been&broken.&&
- rocks&get&broken&by&fault&à&a&lot&of&energy&or&Earthquakes.&
brittle&failure-&Rocks&will&break&
- processes&usually&happen&at&fairly&shallow&depths&in&the&earth’s&crust.&Fairly&
shallow&depths&where&rocks&are&cold.&&
Plastic&deformation-&Deeper,&when&rocks&are&warmed&upà&bend&and&fold&
&
Complex&folding&and&deformation&(faulting,&folding)à&some&places&in&the&world,&
the&youngest&rocks&can&be&at&the&bottom&and&the&oldest&rocks&have&been&pushed&
over&them&
&
Isotopes-&chemical&species&that&are&unstable&and&produce&daughter&products.&
- used&in&the&steady&decay&of&unstable&isotopes&to&know&the&absolute&age&
isotope!dating!or!radiometric!dating-!the&rate&at&which&isotopes&break&down&is&
known.&It’s&at&a&steady&constant&rate.&Using&laboratory&methods,&we&can&
determine&the&ratios&between&the&amount&of&parent&isotope&and&daughter&
product&in&a&rock&which&gives&the&absolute&age.&!
&&
Uranium!238-&it’s&unstable&and&breaks&down&by&radioactive&decay&
and&the&end&daughter&product&is&lead,&Pb,!lead.&&
- Measure&the&amount&of&uranium&238&in&lead&in&a&sample.&Look&at&the&ratio&
between&the&two&amounts&and&that&gives&us&some&idea&of&age.&
&&
&
half-life=&rate&of&decay&
- different&with&different&isotopes&
- the&amount&it&takes&for&half&of&the&parent&isotope&to&be&turned&into&lead.&
- Some&break&down&very&quickly.&They&have&half-lives&of&hours&or&days.&Other&
isotopes&have&half-lives&of&millions&of&years.&&

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geologic!time!scale-!&
Unconformity-&&So&the&layers&on&top&are&sitting&uncomfortably&on&the&rocks&
underneath.&
Older&layers&in&the&strata&are&not&flat.&It’s&been&tilted&by&tectonic&processes.&
Dip=&tilt&
Plutons-&&The&bodies&of&igneous&rocks&which&have&come&up&from&depth&and&
intruded&younger&rocks.&Granite&pluton&that’s&intruded&in.&It’s&been&intruded&as&a&
molten&magma.&
- &Then&this&layer&was&depositedàThompson&River&formation.&
&Sedimentary!basins-!!substance&of&the&earth’s&crust&which&allows&deposition&of&
sediment&over&broad&areas.&
&
Geologists&name&layers&after&the&local&place.&So&there&is&a&place&called&
Revelstoke,&Kamloops&in&British&Columbia&
&
Formation-&refers&to&a&distinct&strata.&Example,&Revelstoke&formation&
- have&distinctive&fossils&or&structures&in&it.&It&may&have&
distinctiveàconformable&succession,&but&even&in&there,&there&are&slight&
breaks.&And&these&are&called&disconformities&not&unconformities&
- unconformity&is&where&someone&has&ripped&out&three&chapters&out&of&your&
book.&&
- disconformity&is&where&someone&has&ripped&out&a&page.&&
- Disconformity&generalizes&a&mini&unconformity.&
The&disconformities&is&more&than&what&is&recorded&in&the&rock.&More&gaps&
than&record.&
Index!fossil-&used&&to&correlate&it&across&large&areas.&
Ex:&&Canyon&and&Australia,&they’re&separated&by&oceans&today&but&during&Pangea&
or&Rodina,&those&places&were&quite&close.&Using&index&fossils,&gaps&are&recognized.&
Index&fossils&are&missing.&Volcanic&ash&and&a&lot&of&volcanic&eruptionà&short&lived.&&
Ash!layers-&give&a&high-resolution&correlation&from&one&area&to&another.&
Thus,&it&can&be&dated.&Then,&you&can&match&rocks&elsewhere&based&on&the&
presence&of&volcanic&ash&arising&since&the&deposition&of&ash&is&virtually&
instantaneous.&&
&Example:&A&type&of&fossil&lived&over&many&millions&of&years.&We&find&it&in&all&
layers.&It&wouldn’t&be&any&use&as&an&index&fossil&because&it’s&common.&We&
want&those&types&of&fossils&that&are&actually&rare&because&they&only&record&
very&short&instances&of&time.&
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