Origin of organisms on earth in various time period.

2. OVERVIEW
The total life span of the earth
from the time of its origin is called
Geological time.
The geological time scale is a
record of the life forms and
geological events in earths history.
Aim of time scale by studying
earth layers and fossils worldwide.
Radio active dating helped
determine the absolute divisions in
the time scale and it helps
understand the evolution of earth

3. Change of Earth
Available evidence indicate that the age of earth is about 5
billion years. Change of earth classified the following manner
1. Changes Occur Suddenly: Catastrophism
a. Catastrophism: the principle that states that all geologic
change occurs suddenly.
b. Supporters of catastrophism thought that Earth’s features,
such as mountains and
seas, formed during sudden events called catastrophes.
2. Changes Occur Gradually: Uniformitarianism
a. About 250 years ago, James Hutton established a principle
that is now known as uniformitarianism.
b. Uniformitarianism: the idea that the same geologic
processes that shape Earth today have been at work
throughout Earth’s history.
c. The principle also states that the average rate of geologic
change is slow and has remained relatively constant over time.

4. Classification of Time
scale
The largest portions are called “eons”
Eons are divided into “eras”
Eras are divided “periods”
Periods are divided into “epochs”

5. Eons
•Earth’s 4.6-billion-year history is divided into
four eons: Hadean, Archean, Proterozoic,
Phanerozoic
•The Hadean, Archean, and Proterozoic eons
together are called Precambrian time.
•Precambrian time makes up almost 90% of
Earth’s history.
•The Phanerozoic Eon, the present eon, is
divided into three eras: the Paleozoic,
Mesozoic, and Cenozoic.
•The periods of the Cenozoic, the present era,
are further divided into epochs.

6. Classification of
Eons

7. Classification of
Eras
Geological time scales consists of 7 major eras
1. Azoic
2. Archaeozoic
3. Proterozoic
4. Palaeozoic
5. Mesozoic
6. Coenozoic
7. Psychozoic

8. The geological time scale. Image by Jonathan R. Hendricks. This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License

9. Eons
•No many changes were observed in the eons of
Hadean, Archean and Proterozoic.
•But the Phanerozoic eon is divided into many
eras
1. Mesozoic
2. Coenozoic
3. Psychozoic

10. Palaeozoic
eras
It is the era of ancient life.
It had duration of about
370 million years (Starting
about 600 & ending by 230
million years ago).
This era was age of
higher invertebrates, fishes
and amphibians.
The Palaeozoic era is
divided into many periods
Periods are

11. Cambrian Period
The rocks were documented and
discovered first in this period.
Duration is 75 million years
Its was started the melting of
glaciers and rise the sea level
Fossils of this period is Algae,
fungi, bacteria, protozoan, sponges,
coelenterates, annelids molluscs
echinoderms,
The primitive arthropods are
plenty and predominant constituted
about 50% of total fauna This painting is a 1997 illustration
of an assortment of Cambrian era
creatures by D.W. Miller.

12. Ordovician Period
Duration is 65 million years.
The first vertebrates
Ostracoderms appear during
this period.
Fossils of Algae, Corals
gastropods & branchiopods
are dominant.
The corals, snails, clams,
Nautilus and echinoderms
made their appearance
during this period.
Ordovician Period fossils

13. Silurian Period
Duration is 35 million
years.
The Land Plants (ferns)
& Air breathing
invertebrates appeared
in this period.
Placoderms and Sea
lilies were predominant. Silurian period fossils

14. Devonian Period
Duration is 45 million years.
It is described as Age of fishes.
Ostraderms are predominant in this period.
First land vertebrate amphibians & Ammonites
group of Cephalapods were appeared .
Land Plants are predominant.
Ammonites fossils Fish fossils

15. Mississippian Period
Duration is 25 million years.
It has dense forests, coal, oil, gas, lead, zinc, gold,
silver, gypsum and rock salts are formed during this
period.
Salamander like amphibians appeared
Sharks and Sea lilies were predominant.
Sea lilies fossils Other fossils from Mississippian period

16. Pennsylvanian Period
Duration is 25 million years.
It has dense insects, few dragon flies with longer
wing span (30 inches). In addition the amphibians
are high and dominant.
First reptiles namely stem reptiles appeared.
Mississippian and Pennsylvanian periods are
together called Carboniferous period because of
rich formation of coal on this earth .
Dragon fossils
First Millipedes

17. Permian Period
During this period greater changes of Climate and
topography
Climate very cold and drier
Dense of hard wood plants and freshwater fish
New genera of beetles dragon and may flies were
appeared.
Also first appearance of reptiles during this period.

18. Mesozoic Era
It is called period of middle life (between Primitive
Palaeozoic & advanced Coenozoic animals).
Duration of this era is 150 million years.
Reptiles are predominant during this period. Hence
it is called Golden age of Reptiles.
Era witnessed the rise and fall of reptiles and the
origin of birds and origin of mammals.
It has three period

19. Triassic Period
It is first period of Mesozoic era.
Duration of this period is 60 million years.
Climate was very harsh and dry
Dinosaurs and Pterosaurs originated during this
period
Egg laying mammals was originated
Some of the primitive amphibians are extinct
during this period.

20. Jurassic Period
It is second period of
Mesozoic era.
Duration -30 million years
The climate was warm and
humid.
Dinosaurs multiplied and
dominated
Toothed birds and
insectivores appeared
Archaeopteryx, the fossil
connecting link was
discovered.
Archaeopteryx- connecting link
between reptiles and birds

21. Cretaceous Period
It is third period of
Mesozoic era.
Duration -60 million
years
Dinosaurs and toothed
bird become extinct
Morden birds and
Archaic mammals are
originated.

22. Coenozoic Era
The Cenozoic era represented up to the present.
It is age of Mammal.
Man appeared during this era.
It has two periods namely
1. Tertiary
2. Quaternary
The Giant Mammals of the Cenozoic Era

23. Era
Traditional
Periods
New Periods Epochs
CenozoicEra
Quaternary Period Neogene
Period
Holocene Epoch
Pleistocene Epoch
Tertiary Period
Pliocene Epoch
Miocene Epoch
Paleogene
Period
Oligocene Epoch
Eocene Epoch
Paleocene Epoch
Coenozoic Era

24. Period Epoch Continental Positions New Mammals
N
e
o
g
e
n
e
Pliocene
 Africa closes off the
Mediterranean Sea
 North and South
America join at
Panama
 The Geography of the
earth similar to today
 First hominids-
human ancesters
Miocene
 Africa is pushing into
Europe-forms the Alps
 Arctic becomes
covered with ice
 Horses,camels,and
rhinos
 Beaver-like animals
 many apes and
other primates

25. P
a
l
e
o
g
e
n
e
Oligocene
 Australia separates from
Antarctica
 India crashes into Asia-
forms Himalayans
 Antarctica is covered by
glaciers
 Sea levels are low
 Dogs, cats, and
pigs
 toothed whales
Eocene
 Europe and North America
separate
 Bats
 Elephant ancestors
 Whales
 Eohippus-the first
horse
Paleocene
 Europe is joined with North
America
 Australia is joined with
Antarctica
 India a land unto itself
 Atlantic Ocean is forming
 The condylarths-
ancestors of
modern hoofed
herbivores
 Rodents
 The first Primates

26. https://www.digitalatlasofancientlife.org/learn/geological-
time/geological-time-scale/
https://www.wahpeton.k12.nd.us/ourpages/auto/2015/8/20/53494933/
U2%20L4%20Notes.pdf
https://www.fossils-facts-and-finds.com/
Reference

27. Thank you
For any Clarification Contact;
Dr. T. RAMESH
Assistant Professor of Zoology
PG & Research Department of Zoology
Vivekananda College Tiruvedakam
+91 99420 58831
faunaldiversity@gmail.com