Geological time scale and plant life through ages

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1. GEOLOGICAL TIME SCALE
AND
PLANT LIFE THROUGH AGES
DR. RIMI ROY
J. K. COLLEGE
PURULIA

2. Geological time scale
•Thetotallifespanoftheearthfromitsorigin
iscalledgeologicaltime.Theavailable
evidenceindicatethattheageofearthis4500
million(4.5billion)years.
•Theeras,periods,andepochsofthe
geologicaltimearearrangedinanorderly
mannerandthisarrangementiscalled
geologicaltimescale.

3. •Theprimarydefineddivisionsoftimeareeons,insequence
theHadean,theArchean,theProterozoicandthePhanerozoic.
Thefirstthreeofthesecanbereferredtocollectivelyas
thePrecambriansupereon.Eonsaredividedintoeras,whicharein
turndividedintoperiods,epochsandages.
•Era-Ageologiceraisasubdivisionofgeologictimethatdivides
aneonintosmallerunitsoftime.ThePhanerozoicEonisdivided
intothreesuchtimeframes:thePaleozoic,Mesozoic,
andCenozoicrepresentthemajorstagesinthemacroscopicfossil
record.
•Period-Ageologicperiodisoneofseveralsubdivisionsofgeologic
timeenablingcross-referencingofrocksandgeologiceventsfrom
placetoplace.
•Epoch-Ingeochronology,anepochisasubdivisionofthegeologic
timescalethatislongerthananagebutshorterthanaperiod.The
currentepochistheHoloceneEpochoftheQuaternaryPeriod.
•Age-Ageologicageisasubdivisionofgeologictimethatdivides
anepochintosmallerparts.

6. Eon Era
Time frame (Ma= million years
ago)
Phanerozoic
Cenozoic 66million years agoto present
Mesozoic 251.902to66million years ago
Paleozoic 541to251.902million years ago
Proterozoic
Neoproterozoic 1,000to541million years ago
Mesoproterozoic 1,600to1,000million years ago
Paleoproterozoic 2,500to1,600million years ago
Archean
Neoarchean 2,800to2,500million years ago
Mesoarchean 3,200to2,800million years ago
Paleoarchean 3,600to3,200million years ago
Eoarchean 4,000to3,600million years ago
Hadean(unofficial) not officially divided into eras
Formation of
Earthto4,000million years ago

11. Plant life through ages
•Fossilevidenceforcyanobacteriacomesinthefossil
recorddeepintothePrecambrianaround3000Ma.
•Paleozoicflora
1.Cambrianflora:earlyplantsweresmall,unicellularorfilamentous,with
simplebranching.Agroupofcalcareousgreenalgae,Dasycladalesfound
inthefossilrecordsincethemiddleCambrian.Thesealgaedonot
belongtothelineagethatisancestraltothelandplants.Othermajor
groupsofgreenalgaehadbeenestablishedbythistime,buttherewere
nolandplantswithvasculartissuesuntilthemid-Silurian.
2.Ordovicianflora:firstextensiveappearanceofsporesinthefossilrecord.
Thefirstterrestrialplantswereprobablyintheformoftinyplants
resemblingliverwortswhen,aroundtheMiddleOrdovician,evidencefor
thebeginningoftheterrestrializationofthelandisfoundintheformof
tetradsofsporeswithresistantpolymersintheirouterwalls.Theseearly
plantsdidnothaveconductingtissues,severelylimitingtheirsize.They
were,ineffect,tiedtowetterrestrialenvironmentsbytheirinabilityto
conductwater,likeextantliverworts,hornworts,andmosses.

12. 3.Silurianflora:hefirstfossilrecordsofvascularplants
appearedintheSilurianperiod.Theearliestknown
representativesofthisgroupareplacedinthe
genusCooksonia.BytheendoftheSilurianmuchmore
complexvascularplants,thezosterophylls,haddiversified
andprimitivelycopods,suchasBaragwanathiahadbecome
widespread.
4.Devonianflora:BytheLateDevonian,forestsoflarge,
primitiveplantsexisted:lycophytes,sphenophytes,ferns,
andprogymnospermshadevolved.Mostoftheseplants
havetruerootsandleaves,andmanywerequitetall.The
tree-likeArchaeopteris,ancestraltothegymnosperms,and
thegiantcladoxylopsidtreeshadtruewood.Bytheendof
theDevonian,thefirstseed-formingplantshadappeared.

13. 5.Carboniferousflora:ThemainEarlyCarboniferousplantswere
theEquisetalesincludedCalamitesand(Horse-tails),Sphenophyllales
(scramblingplants)likeSphenophyllum,Lycopodialeslike
Lepidodendron(Clubmosses),Lepidodendrales(arborescentclubmosses
orscaletrees),Filicales(Ferns)likeCaulopterisand
Megaphyton,Medullosales(previouslyincludedinthe"seedferns",an
artificialassemblageofanumberofearlygymnospermgroups)and
theCordaitaleslikeCardiocarpus.Thesecontinuedtodominate
throughouttheperiod,butduringlateCarboniferous,severalother
groups,Cycadophyta(cycads),theCallistophytales(anothergroupof
"seedferns"),andtheVoltziales(relatedtoandsometimesincluded
undertheconifers),appeared.
6.Permianflora:ThePermianbeganwiththeCarboniferousflorastill
flourishing. In mid-permian, lycopod trees
likeLepidodendronandSigillaria,werereplacedbythemoreadvanced
conifers.Theginkgosandcycadsalsoappearedduringthisperiod.

14. •Mesozoicflora
1.Triassicflora:Onland,theholdoverplantsincludedthelycophytes,
thedominantcycads,Ginkgophyta(representedinmoderntimes
byGinkgobiloba)andglossopterids.Thespermatophytes,orseed
plantscametodominatetheterrestrialflora:inthenorthern
hemisphere,conifersflourished.Dicroidium(aseedfern)wasthe
dominantsouthernhemispheretreeduringtheEarlyTriassicperiod.
2.Jurassicflora:Extantconiferfamiliesthatflourishedduringthe
Jurassic
includedtheAraucariaceae,Cephalotaxaceae,Pinaceae,Podocarpace
ae,TaxaceaeandTaxodiaceae.TheextinctMesozoicconifer
familyCheirolepidiaceaedominatedlowlatitudevegetation,asdid
theshrubbyBennettitales.Cycads,Ginkgoandtreefernswerealso
common.
3.Cretaceousflora:Thefirstrepresentativesofmanymoderntrees,
includingfigs,planesandmagnolias,appearedintheCretaceous.At
thesametime,someearlierMesozoicgymnosperms,likeConifers
continuedtothrive,althoughothertaxalikeBennettitalesdiedout
beforetheendoftheperiod.

15. •Cenozoic flora
•It was the age of savannas and other flowering
plants. At 35 Ma,grassesevolved from among
the angiosperms.