PP29_Geological_time_scale_and_cambrian_explosion_1471878457.ppt

geological time scale

1. Life sciences Grade 10
CAPS: structured, clear, practical
Helping teachers unlock the power of NCS
KNOWLEDGE AREA: Diversity, change and continuity
Topic 12: History of life on Earth
Geological time scale and Cambrian explosion and
Pre-Cambrian

2. Agenda or Summary Layout
The Geological Time-Scale
1
2
3
Discussion Item One
The Geological Time-Scale
Discussion Item Two
The Beginning of Life
Discussion Item Three
Cambrian Explosion

3. The Geological Time-Scale
The Geological Time-Scale
The Earth’s Geological Time Scale

4. The Geological Time-Scale
Remember that the history of life took place millions
and millions of years ago.
Therefore scientists had to develop a time scale that
uses bigger units than century.
This time scale is called the Geological Time-Scale.
What does it mean?

5. The Geological Time-Scale
This time scale divides the Earth’s history into three main eras.
These eras are the Paleozoic, Mesozoic and the Cenozoic .
This goes back to about 543 million years ago.
These eras are then divided into time periods.
There are about 13 time periods like Triassic, Jurassic and
Neogene.
Then the Cenozoic time period is divided into smaller time
periods called an Epoch.
Before the Cambrian period is described as the Pre-Cambrian
Time .
How does it work?

6. Something for you to do.
1. Describe the time period in which you live using the
geological time-scale.
2. How long ago did the Holocene Epoch begin?
3. Can you describe 10 000 years in million years?
Can you answer this question?

7. Solution
1. Holocene Epoch of the Quaternary Period of the
Caenozoic Era.
2.10 000 years ago.
3. 0.01 million years ago
The answer is…

8. The Geological Time-Scale
Scientists believe that the Earth began about 4-6 million
years ago.
It was a huge ball of fire with rocks and burning gas.
When it cooled, gases were released from the inside it.
Hydrogen, methane, ammonia and nitrogen were the main
gases.
Water vapor was also present. It formed from the water
that was found on the Earth’s surface.
How did life begin?

9. The Geological Time-Scale
These gases together with the water vapour formed the
atmosphere.
Notice that there is no oxygen.
However some scientists believed that oxygen was present in
very small quantities.
A Russian scientist A.I Oparin and an English scientist J. B. S
Haldane put forward an hypothesis about how life began in the
1920’s.
They hypothesized that uv light and lightening changed these
gases into organic molecules.
How did life begin?

10. The Geological Time-Scale
These organic molecules were proteins and fatty acids.
These molecules combined to form the cell membranes.
It is believed that this was how cells were formed.
Fossil evidence suggests that cells existed from about 3.4
billion years ago.
However there is no fossil evidence on how they formed
because gases and liquids do not form fossils.
How did life begin?

11. The Geological Time-Scale
The hypothesis put forward by Oparin and
Haldane was tested by Stanley Miller in 1953.
Miller worked under the guidance of
Harold Urey at the University of Chicago.
In his experiment he pumped out the air of the closed
apparatus.
The air was replaced with water vapour, methane, hydrogen and
ammonia.
How did life begin?

12. The Geological Time-Scale
At that time Earth experienced violent storms, Miller
recreated this by heating the water and passing the
gases past a high voltage electric spark.
The electric spark represented the lightening.
After a week the contents of the flask had turned red.
These contents were then removed and studied.
Miller found amino acids and other organic compounds.
How did life begin?

13. The Geological Time-Scale
However there were scientist that did not support
Miller’s findings.
They believed that primitive Earth did contain oxygen
and that the levels of oxygen were high enough to
prevent the formation of organic compounds.
How did life begin?

14. The pre-Cambrian times
occurred before the
Cambrian Period.
Scientist often describe
the time or year in
which a particular
organism evolved or
arose as the year or
time period in which
the first fossil appeared.

The chart alongside is
based on these fossil
findings.
Life During the Pre-Cambrian Times.
Before 543 million years ago

15. Something for you to do.
Can you do this?
Answer this question.

16. The information shown in the chart in the can
be translated into a time line.
  0.5- Earliest Animals
1.0-
Billions of 1.5- Earliest prokaryotes
years ago 2.0-
2.5- Accumulation of oxygen
3. 0- } different types of bacteria
3.5- Prokaryotes (photosynthetic bacteria)
4.0- Possible origin of earliest life forms
4.5- Formation of Earth
 
 

17. The Cambrian Explosion
This period lasted for about 38 million years
It started 543 million years ago and lasted until about 505 million
years ago.
The most notable happening during this period was the
explosion of the animal groups.
The animals suddenly appeared in the first 5 to 20 million years.
These animals appeared on Earth in a very short period of time.
The animal explosion.

18. The Cambrian Explosion
The fossil record shows the major animal
groups appeared as follows:
• the coelenterates520 million years ago
• sponges 540 million years ago
• molluscs 536 million years ago
• arthropods 513 million years ago
• chordates 524 million years ago
• annelids 520 million years ago
• echinoderms 518 million years ago
The animal explosion.

19. End of the Cambrian times to the modern
period
The epoch in which we now live is called the Holocene
epoch. We shall now look at the history of life from the
end of the Cambrian time until the modern epoch.
Based on fossil records scientists think that the
following organisms appeared as follows:
• fish about 438 million years ago
• amphibians about 380 million years ago
• reptiles about 385 million years ago
• birds about 180 million years ago
• mammals about 150 million years ago
• humans about 150 000 to 200 000 years ago
History of life from the end of the Cambrian period to the Holocene Epoch

20. End of the Cambrian times to the modern
period
The first bipedal animals of the human family appeared about 2
million years ago.
According to the fossil records there were many species of these
bipedal ape- like ancestors.
They showed a gradual increase in height, brain size and a
gradual flattening of the face.
It is believed the earliest ape-like ancestors of humans lived
millions of years ago in Africa.
Human history

21. Terminology
Geological Time-Scale: the time scale that is used to trace the
history of life.
Eras: these are the time period in which the Earth’s history is
divided into.
Time periods: are the smaller time periods that the eras are
divided into
Epoch: is the smaller time period into which the time periods of
the Caenozoic Era is divided into.
Pre-Cambrian Time : is the period before the Cambrian period.
These are the terms you must know

22. Something for you to do
1.The three main Eras of Earths history.
A. Paleozoic, Mesozoic and Caenozoic
B. Holocene, Paleozoic and Triassic
C. Quaternary, Mesozoic and Triassic
D. Caenozoic, Triassic and Paleozoic

23. 2.The periods of the Caenozoic Era is called…
A. Era
B. Time period
C. Epoch
D. Cambrian

24. 3.The gases found on Earth 4-6 billion years ago…
A. Oxygen, methane and nitrogen
B. Hydrogen, carbon and oxygen
C. Hydrogen, methane and ammonia
D. Nitrogen, oxygen and water.

25. 4.The two scientists that hypothesized that uv light
and lightening changed the gases found on earth
into organic molecules are…
A. Miller and Urey
B. Oparin and Haldane
C. Oparin and Urey
D. Miller and Oparin

26. 5.The scientist that tested the above hypothesis was
called…
A. Miller
B. Oparin
C. Urey
D. Haldane

27. 6.The earliest life forms of the pre-Cambrian times
were…
A. Prokaryotes
B. Eukaryotes
C. Humans
D. Fish

28. 7.The earliest eukaryotes developed about ___ years
ago.
A. 0.5
B. 1.5
C. 2.0
D. 4.5

29. 8.The organism that was responsible for releasing
oxygen into the atmosphere during the pre-
Cambrian times were…
A. Fungi
B. Plants
C. Photosynthetic cyanobacteria
D. bacteria

30. 9.The first organisms of the animal kingdom appeared
____ thousand years ago.
A. 200
B. 150
C. 610
D. 300

31. 10.The Holocene belongs to the _____ period.
A. Quaternary
B. Neogene
C. Palaeocene
D. Triassic

32. 11.The Neogene period is a part of the ___ era.
A. Caenozoic
B. Mesozoic
C. Paleozoic
D. None of the above.

33. 12.The Cretaceous period began about ___ million
years ago.
A. 4500
B. 0.01
C. 144
D. 208

34. 13.The gas that was in extremely small quantities or
completely absent when life on Earth began.
A. Methane
B. Hydrogen
C. Ammonia
D. Oxygen

35. 14.The gas that increased in the Earth’s atmosphere
when the photosynthetic bacteria developed.
A. Methane
B. Hydrogen
C. Ammonia
D. Oxygen

36. 15.The geological time period that we are now living in.
A. Quaternary
B. Neogene
C. Palaeocene
D. Triassic

37. 16.The geological time period in which the major
groups of animals appeared.
A. Cambrian
B. Triassic
C. Jurassic
D. Permian

38. 17.The geological time period when the dinosaurs
flourished.
A. Cambrian
B. Triassic
C. Jurassic
D. Permian

39. 18.The oldest phyla of invertebrates that appeared on
Earth.
A. Coelenterates
B. Sponges
C. Molluscs
D. Arthropods

40. Solution:
1.A
2.C
3.C
4.B
5.A
6.A
7.B
8.C

41. 9.C
10.A
11.A
12.C
13.D
14.D
15.A
16.A
17.C
18.D