Presented by

D r. A PA R N A M. YA D AV

A s s i s t a nt Pro f e s s o r

D ep t . o f B o t a n y

J . M. Pa t e l C o l l eg e o f A r t s , C o m m e r c e & S c i e n c e ,

B h a n d a r a

What is Geological Time Scale ?

• Sequence of geological periods in the Earth’s history is geological time scale.

• The GTS is a system of chronological dating that relates geological strata

(stratigraphy) to time, and is used by geologists, palaeobotonists,

palaeontologists and other Earth scientists to describe the timing and

relationships of events that have occurred during Earth’s History.

• GTS is put in a tabular form where sequence of geological periods in the

history of Earth is shown.

• This table also shows “length of time occupied by different geological

periods” and the unit of measurement of time is “millions of years”

[1 Million = 10, 00, 000 years].

What is Geological Time Scale ? …..

• The table of geological timescale was constructed by studying rock strata,

which was exposed by excavation, mining or where rivers have cut deeply

into the Earth crust.

• With the knowledge of rate of erosion and rate of deposition, the interval

occupied by different periods can be roughly estimated by measuring the

relative thickness of the rock strata. More accurate dating can be done by

radiometric dating.

• Also the fossils found in each strata have been studied and their age was

determined.

• Units were named as they were discovered. Sometimes unit names were borrowed from

local geography, from a person, or from the type of rock that dominated the unit.

Examples-

• Cambrian: From the Latin name for Wales. Named for exposures of strata found in a type-section

in Wales by British geologist Adam Sedgwick.

• Devonian: Named after significant outcrops first discovered near Devonshire, England

• Jurassic: Named for representative strata first seen in the Jura Mountains by German geologist

Humboldt in 1795

• Cretaceous: From the Latin “creta” meaning chalk by a Belgian geologist

Major divisions and subdivisions of GTS

• GTS has been divided into two major groups called Eon.

• These eons are then subdivided into Eras.

• Each era has been subdivided into Period.

• Each period has been again subdivided into Epochs.

• These epoch further subdivided into Age.

Major divisions and subdivisions of

GTS…

• Different periods are recognised mainly on the basis of

i. Changes in the composition of fossils &

ii. Occurrence of major geological events

e.g. episodes of mountain building or major changes in sea level.

• The earliest era is the Precambrian, which began around 4600 million years ago. It has very few fossil

records. Abundant fossils have been reported in succeeding eras Palaeozoic era, Mesozoic era and

Cenozoic era.

• The earliest time of the Earth is called the Hadean and refers to a period of time for which we have

no rock record, and the Archean followed, which corresponds to the ages of the oldest known

rocks on earth. These, with the Proterozoic Eon are called the Precambrian / Cryptozoic Eon.

The remainder of geologic time, including present day, belongs to the Phanerozoic Eon.

We are living in the Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch.

Eons:Precambrian: Earliest span of timePhanerozoic: Everything since

Eras:PaleozoicMesozoicCenozoic

Periods:CambrianOrdovicianSilurianDevonian

Carboniferous (Missipp. & Pennsylvanian)

PermianTriassicJurassicCretaceousPaleogeneNeogeneQuaternary

Epochs:PaleoceneEoceneOligocene

MiocenePliocene

PleistoceneHolocene

Paleozoic“Age of

Invertebrates”

Mesozoic “Age of Reptiles”

Cenozoic“Age of

Mammals”

The Earth Through Time

• 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 in

Archean period and it became more complex and successful over

the next 3 billion years: Prokaryotes then Eukaryotes

• Cyanobacteria begins producing free oxygen (photosynthesis).

• First simple multi celled animals appear.

• Land masses gather to make up a continent called “Rodinia”

The Cambrian Period:

• Explosion of life

• All existing phyla come into being at this time

• Life forms in warm seas as oxygen levels rise enough to support

life

• Dominant animals: Marine invertebrates (trilobites and

brachiopods)

• Supercontinent Gondwana forms near the South Pole (note

position of present-day Florida)

The Proterozoic Period:

9

The Ordovician period:

The Silurian period:

• The 1st animals with bones appear, though dominant animals are

still trilobites, brachiopods and corals

• The beginning of the construction of South Carolina

• A very cold time in Earth’s history: there was a great extinction

due to ice caps in present-day Africa

• Four main continents: Gondwana, Baltica, Siberia and Laurentia

• First land plants appear and land animals follow.

• Bryophytes evolved.

• Laurentia collides with Baltica and closes Iapetus Sea.

• Coral reefs expand and land plants begin to colonize barren

land.

• First millipede fossils and sea scorpions (Euryptides) found in

this period

10

• Pre-Pangea forms. Dominant animal: fish

• Oceans still freshwater and fish migrate from southernhemisphere to North America.

• Present-day Arctic Canada was at the equator andhardwoods began to grow.

• Amphibians, evergreens and ferns appear.

• The Acadian Orogeny, leading to S.C. metamorphism

11

Devonian (Age of the Fish)

Mississippian:

• First seed plants appear

• First land vertibrates

• Much of North America is covered by shallow seas

and sea life flourishes (bryoza, brachipods, blastoids)

Pennsylvanian:

• Modern North America begins to form

• Ice covers the southern hemisphere and coalswamps formed along equator.

• Lizards and winged insects first appear.

Permian:

• Last period of the Paleozoic

• Pangea forms. Reptiles spread across continents.

• The Appalachians rise

• Permian-Triassic extinction event occurs 251 Ma.

• 90% of Earth’s species become extinct due to

volcanism in Siberia. This marks the end of trilobites,

ammonoids, blastoids, and most fish.

Triassic:

• First dinosaurs appear

• First mammals- small rodents appear. Life and fauna re-

diversify.

• Gymnosperms evolved at the end of Triassic Period

(225MA) & dominated the earth in Paleocene epoch.

• First turtle fossil from this period

• Pangea breaks apart

Jurassic:

• Pangea still breaking apart.

• Angiosperm evolved during this period.

• Dinosaurs flourish “Golden age of dinosaurs”

• First birds appear

• Atmospheric CO2 levels 4–5 times the present day levels

• North America continues to rotate away from Africa

Cretaceous:

• T-Rex develops

• First snakes and primates appear

• Deciduous trees and grasses common

• First flowering plants established

• Mass extinction marks the end of the Mesozoic Era, with

the demise of dinosaurs and 25% of all marine life.

Tertiary:

• First horses appear and tropical plants dominate

(Paleocene)

• Grasses spread and whales, rhinos, elephants and other

large mammals develop.

• Sea level rises and limestone deposits form

• Aapes appear (Oligocene) & Hominids develop

• Horses, mastadons, camels, and tigers roam free

• Modern mammal and bird families become recognizable

• Grand Canyon forms (Pliocene)

Quaternary:

• Modern humans develop and ice sheets are predominant-

Ice age (Pleistocene)

• Holocene Humans flourish (Holocene)