Lectures on earth geology

1. Department of Civil Engineering
GEOLOGY Lecture-8
Topic – Geological Time Scale
Faculty - Er. Arpit Singh Bhadoriya
Assistant Professor
Department of Civil Engineering,
Poornima College of Engineering,
ISI-6 RIICO Institutional Area Goner Road, Jaipur

2. Geologic
Time
Scale
A BRIEF HISTORY OF
EARTH SINCE 4.6
BILLION YEARS.

3. Measuring
Time
•
•
•
The Geological time
scale is a record of the
life forms and
geological events in
Earth’s history.
Scientists developed
the time scale by
studying rock layers
and fossils world
wide.
Radioactive dating
helped determine the
absolute divisions in
the time scale.

4. Giving Time a
Name
• The largest sections are called “eons”.
• “Eons” are divided into “eras” (the 2nd
largest section).
• “Eras” are divided into
“periods”.
• ‘Periods’ are
divided into ‘epochs”.

5. Eon
s
• Largest, most general
division of time.
• 2 Eons
• The eons are:
Cryptozoic
(Precambrian) eon
and Phanerozoic eon.
• Precambrian and
Phanerozoic eon both
consists of three eras

6. Era
s
•
•
Each Eon is broken up into
Eras. Major eras in Earth’s
history:
• Archean (4600 mya - 2500
mya)
• Proterozoic (2500 mya - 540
mya)
• Paleozoic (540mya - 250mya)
• Mesozoic (250 mya - 65.5
mya)
• Cenozoic (65.5 mya –
*mya refers to million years
ago.

7. Period
s
• Each Era is divided
into even more
specific blocks of time
called periods.
• Various geologic
events are associated
with each period.
• Each period is again
classified into
different epochs.

8. How is Time
Divided?
•
•
Major changes in Earth’s history mark the
boundaries between the sections.
Most sections have been divided because a major
organism developed or went extinct in each
section.

9. Cryptozoic eon (Precambrian
time)
•
•
•
•
•
Lasted from 540 million years
ago to 4600 million years ago.
Oldest and longest (covers almost
90% of earth’s history).
simple organisms- bacteria,
algae, protozoa was born.
Oldest rocks that we know were
found in this eon which dates to
about 3.5 billion years old.
Divided into 2 eras: Proterozoic
and Archean era.

10. Archean
era
• Lasted from 2500 million
years ago – 4600 million
years ago.
• Earliest plants (marine
algae) developed.
• The first life bacteria came
into existence (3800 million
years ago).
• The oldest rocks (3500
million years ago) were
formed in this era.

11. Proterozoic
era
• Lasted from 540 million
years ago to 2500 million
years ago.
• Marine invertebrates
were probably common,
few with shells.
• Glaciations took place in
this era, probably
worldwide.

12. Phanerozoic
eon
• Begin from 540 million years
ago and is still continuing
today.
• Divided into three eras:
i) Paleozoic era (Past life)
ii)Mesozoic era (Middle
life) iii)Cenozoic era
(Present life)

13. Palaeozoic
Era
•
•
•
•
Began 570 million years ago
and ended 250 million years
ago.
Divided into 6 periods
(Permian, Carboniferous
period, Devonian, Silurian,
Ordovician, Cambrian).
For the first time on Earth,
organisms had hard parts
(shells, exoskeletons).
Evolution and development of
pteridophytes, amphibians,
reptiles, fishes, wing bearing
insects, trilobites etc.

14. Mesozoic
era
• Lasted from 250 million
years ago to 65 million
years ago.
• Popularly known as Time
of Reptiles.
• Divided into three periods:
Triassic, Jurassic and
Cretaceous.
• Dinosaurs, mammals
and gymnosperms

15. Cenozoic
era
• From 65 million years
ago to present days.
• Divided into two
periods: Tertiary and
Quarterny.
• Development of
modern mammals,
angiosperms and
human beings.

16. Phanerozoic Eon in
brief:

17. IMPORTANT PERIODS IN THE
HISTORY OF EARTH
i) Carboniferous Period
It lasted from 360 million years to
300 Million years. It is an
important period of Paleozoic
era.
During this period, first
reptiles and pteridophytes
were formed and coal plants
got spread. The dead
bodies got buried in this
period forming the coals that we
use today.

18. ii)
Permian
It lied between 300 million
years to 250 million years. It
is also an important period of
Palaeozoic
era. Largest mass
extinction happened in
this period.
Scientists are not sure what
caused this mass
extinction (maybe climate
change & volcanoes).

19. iii)
Jurassic
Jurassic is an important
period of Mesozoic era. It
lasted from 250 million
years ago to 200 million
years ago. During this
period, first birds and
mammals were formed.
Gymnosperms were
dominating plants. The
dinosaurs were formed in
Triassic period reached at
their peak in this period.

20. iv)
Cretaceous
It is a period of Mesozoic era
which lasted from 150 million
years ago to 65.5 million years
ago. It marked the end of the
Mesozoic Era and the
beginning of the Cenozoic
Era. All of the dinosaurs and
half of the other animals &
plants went extinct in this
period. Scientists think an
asteroid hit Earth, the dust
clouds blocked out the sun.
As a result, plants died, then
herbivores, then carnivores.

21. v)Quarternery
period
It is a period of Cenozoic
era which has been
lasting from
1.8 million years ago to
present days. In this
period, the humans
evolved as the most
intelligent creature of
earth and took over. It is
divided into 2 epochs
namely: Pleistocene and
Holocene.