geological time scale

1. Geological time scale
Dr. P. Nithiya
Assistant Professor
Department of Botany
Seethalakshmi Ramaswami college
Trichy- 620002

2. Geological time scale
• Geological time scale is a table showing the
sequence of geological periods in the history of
earth.
• It also shows the lengths of time different
geological periods are assumed to have occupied
It is measured in millions of years.
• It has been constructed by studying rock strata,
where these have been exposed by excavations
or mining or where rivers have cut deeply into
the earth’s crust.

3. • By the technique of radiometric dating (i.e. by
measuring the rates of decay of radioactive
materials in the rocks) more accurate dating
can now be provided.
• In the table of geological time scale, the
results of all such works are summarized.

4. Geological time scale

5. • Table also shows the types of plants that have
been found during different periods.
• The earth has been estimated to be about
4600 million years old.
• Life is believed to have originated about
3000-3500 million years ago on the earth.

6. Million years
• 1 million years = 1,000,000 years
• 10 lakhs years
• 4600 million years= 4,600,000,000 years
• 4,60,00,00,000 years ago

7. Earth formation-4600 million years

8. Major Divisions and Subdivisions of
Geological Time Scale:
• Geological time has been divided into some
major divisions called eras .
• Each era has been divided into periods, which
are then subdivided into epochs.

9. Era
Periods
Epoch
Eon

10. Eon
• An eon is a really, really, super-long,
impossible-to-measure length of time.
• The first principal subdivision is called “Eon”
• Eon goes back to the Greek aiōn, "age.“
• An age is not easy to measure, and neither is
an eon.
• Both are just really long periods of time, but
in science an eon is about a billion years.

11. Eon
• Eon is the spans hundreds to 1000 million
years
Eon
No Life forms Life forms till date
Precambrian Phenerozoic

12. Precambrian
• The Precambrian (or Pre-Cambrian, sometimes
abbreviated pЄ, or Cryptozoic) is the earliest part
of Earth's history, set before the
current Phanerozoic Eon.
• The Precambrian is so named because it
preceded the Cambrian, the first period of the
Phanerozoic eon, which is named after Cambria,
the Latinised name for Wales, where rocks from
this age were first studied.
• The Precambrian accounts for 88% of the Earth's
geologic time.

13. Precambrian

14. Phenerozoic
• The Phanerozoic Eon is the current geologic
eon in the geologic time scale, and the one
during which abundant animal and plant life has
existed.
• It covers 541 million years to the present, and
began with the Cambrian Period when animals
first developed hard shells preserved in the fossil
record.

15. Phenerozoic eon
After completion of precambrian eon, which
continues up to today

16. Hierarchy of geological time scale

17. • Eon: Half billion years or more
• Era: Several hundred million years
• Epoch: Tens of million years
• Age : millions of years

18. Era
• A geological era is a very long division of
geological time, lasting tens of millions of years.
• Its beginning and end are recognized by major
changes in layers of rocks and fossils in the earth.
• As mentioned above, the earliest era is
Precambrian It began about 4600 millions of
years ago.
• Its duration has been 4030 millions of years.

19. Classification of Era
There are four Era in Phenerozoic eon
Precambrian
Paleozoic
Mesozoic
Coenozoic

20. Riddles
• Press the pale button to message the Center
Precambrian
Paleozoic
Mesozoic
Coenozoic

21. • Palaeozoic era began about 570 millions of
years ago.
• Mesozoic era began about 225 millions of
years ago.
• Cenozoic is the most recent era. It began
about 65 million years ago, after the Mesozoic
era, and it is still continuing.

22. Division of Era
• Eras are divided into periods and epochs.
• So a period is a major subdivision of a geological era.
• Major periods of Paleozoic era are
Permian,
Carboniferous
Pennsylvanian
Mississippian
Devonian,
Silurian,
Ordovician and
Cambrian

23. Mesozoic era
• Mesozoic era began about 225 millions of
years ago.
• Mesozoic era is divided into three periods viz.
Cretaceous,
Jurassic and
Triassic.

24. Cenozoic era
• Cenozoic is the most recent era.
• It began about 65 million years ago, after the
Mesozoic era, and it is still continuing.
• Cenozoic era is divided into two periods viz.
Quaternary and
Tertiary

25. Oldest and recent period of geological
time scale
• The oldest known period of geological time
scale is Cambrian (began about 570 million
years ago)
• while the most recent period is Quaternary
(began about 2.5 million years ago).

26. Major Events of Geological Time Scale
1. Bryophytes evolved on the earth during the
Silurian Period of Paleozoic era (i.e. between
395 to 430 million years ago) and are still
surviving.
2. Pteridophytes evolved sometime in Silurian,
dominated the earth during Carboniferous
and are still surviving.

27. Major Events of Geological Time Scale
3. Gymnosperms evolved sometime at the end
of Triassic Period (i.e. about 225 million years
ago) Mesozoic era, dominated the earth
sometime during Palaeocene epoch (i.e. about
65 million years ago) and are still surviving.
4. Angiosperms evolved during Jurassic Period of
Mesozoic era and are now dominating the
earth in the recent epoch of Quaternary
Period of Cenozoic era.

28. Formation of Life in the earth

29. Thank you