Earth-Science-Lesson-1.pdfhgffhhfdghhhhhhh

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2. Objectives
•1. Recognize the relationship among the units—era, epoch,
and period—into which the geologic time scale is divided.
•2. Distinguish the geologic time scale unit being described.

4. What is the Geologic Time Scale?
Whatdoesthetimescalerepresent?
▪Thegeologictimescaledividesupthehistoryoftheearthbasedonlife-
formsthathaveexistedduringspecifictimessincethecreationoftheplanet.
Thesedivisionsarecalledgeochronologicunits(geo:rock,chronology:time).
▪Mostoftheselife-formsarefoundasfossils,whicharetheremainsortraces
ofanorganismfromthegeologicpastthathasbeenpreservedinsedimentor
rock.Withoutfossils,scientistsmaynothaveconcludedthattheearthhasa
historythatlongprecedesmankind.
4
▪TheGeologicTimeScaleisdividedbythefollowingdivisions:
✓Eons:Longestsubdivision;basedontheabundanceofcertainfossils
✓Eras:Nexttolongestsubdivision;markedbymajorchangesinthefossilrecord
✓Periods:Basedontypesoflifeexistingatthetime
✓Epochs:Shortestsubdivision;markedbydifferencesinlifeformsandcan vary
fromcontinenttocontinent.
TableofContents

5. Whatis theGeologicTime Scale,continued?
▪DuetothefactthatearlygeologistshadnowayofknowinghowthediscoveriesoftheEarth
weregoingtodevelop,geologistovertimehaveputthetimescaletogetherpiecebypiece.Units
werenamedastheywerediscovered.Sometimesunitnameswereborrowedfromlocal
geography,fromaperson,orfromthetypeofrockthatdominatedtheunit.
Examples
▪Cambrian:FromtheLatinnameforWales.Namedforexposuresof
stratafoundinatype-sectioninWalesbyBritishgeologistAdamSedgwick.
▪Devonian:Namedaftersignificantoutcropsfirstdiscoverednear Devonshire,
England
▪Jurassic:NamedforrepresentativestratafirstseenintheJuraMountains byGerman
geologistHumboldtin1795)
▪Cretaceous:FromtheLatin“creta”meaningchalkbyaBelgiangeologist
▪TheearliesttimeoftheEarthiscalledtheHadeanandreferstoaperiodoftimeforwhichwehavenorock
record,andtheArcheanfollowed,whichcorrespondstotheagesoftheoldestknownrocksonearth.These,with
theProterozoicEonarecalledthePrecambrianEon.Theremainderofgeologictime,includingpresentday,belongs
tothePhanerozoicEon.
▪Whiletheunitsmakingupthetimescalearecalledgeochronologicunits,theactualrocksformedduringthose
specifictimeintervalsarecalledchronostratigraphicunits.Theactualrockrecordofaperiodiscalledasystem,so
rocksfromtheCambrianPeriodareoftheCambriansystem.
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6. Millennium
Century
Decade
Year
Month
Day
Subdivisions of Human Time
longer shorter

7. Eon
Era
Period
Epoch
Stage
Substage
Subdivisions of Geologic Time
longer shorter

8. Modern Geologic Time Scale
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Four Eons of Geologic Time

9. Modern Geologic Time Scale
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
“Hidden Eon”
“Ancient Eon”
“Earlier Life”
“Visible Life”

10. Modern Geologic Time Scale
Paleozoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Mesozoic Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Cenozoic Tertiary
Holocene
Quat.
Paleogene
Neogene
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Carb.
Quat. = Quaternary
Carb. = Carboniferous
Ma
65
RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Eons

11. Modern Geologic Time Scale
Paleozoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Mesozoic Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Cenozoic Tertiary
Holocene
Quat.
Paleogene
Neogene
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Carb.
Quat. = Quaternary
Carb. = Carboniferous
Ma
65
RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Eras

12. Modern Geologic Time Scale
Paleozoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Mesozoic Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Cenozoic Tertiary
Holocene
Quat.
Paleogene
Neogene
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Carb.
Quat. = Quaternary
Carb. = Carboniferous
Ma
65
RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Periods

13. Modern Geologic Time Scale
Paleozoic
Ordovician
Cambrian
Silurian
Devonian
Mississippian
Pennsylvanian
Permian
Mesozoic Triassic
Jurassic
Cretaceous
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
Cenozoic Tertiary
Holocene
Quat.
Paleogene
Neogene
540
510
439
408
360
323
290
245
208
146
57
35
23
5
1.6
.01
0
Carb.
Quat. = Quaternary
Carb. = Carboniferous
Ma
65
RIP
Hadean
Archean
Proterozoic
Phanerozoic
3800 Ma
4600 Ma
2500 Ma
540 Ma
0 Ma
M
C
P
Epochs

17. HADEAN EON

18. ARCHEAN EON
Earth cooled;
continents and
oceans
emerged;
tectonic plates
processes
began

19. No life possible as the Earth
initially forms 4.6
billion years ago.
Simple, single-celled forms of
life appear 3.8 billion years
ago, becoming more complex
and successful over the next 3
billion years: Prokaryotes then
Eukaryotes
Cyanobacteria begins
producing free oxygen
(photosynthesis)
Land masses gather to make
up a continent called “Rodinia”
PTEROZOIC EON