This document provides an overview of the timeline of life on Earth based on emerging geological and biological evidence. It begins with the earliest geological record of the Earth around 4.6 billion years ago when conditions were violent and chaotic without oxygen in the atmosphere. The first evidence of life appears around 3.5 billion years ago in the form of prokaryotic organisms like bacteria. Around 3 billion years ago, the first photosynthetic cyanobacteria produced oxygen. Eukaryotic, multicellular organisms emerged around 2 billion years ago. The document then outlines the major eras in the timeline of life on Earth from the Paleozoic through the Cenozoic, when humans evolved. It also summarizes theories on the origin

1. Evolving Concept of Life
Based on Emerging Pieces of
Evidence
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2. Target of the Day!
◍ identify the sequence of events of the
history of life on earth;
◍ name the pieces of evidence on the
evolution of life on earth;
◍ recognize the importance of knowing
the history of life on earth
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3. “
What is a timeline?
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4. The Earth’s Timeline
A peek to the early origins of Life
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5. The Earth’s Timeline
◍ 4.6 BYA – Earliest Geologic Record of
the Earth
○ This would also pertain to the “Earth’s Age”
◍ Violent, Chaotic and Disorder
○ 4.6-3.8 BYA - because of the meteorites and
volcanic eruptions. With this condition, zircon
crystal was formed.
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6. The Earth’s Timeline
◍ Early Atmosphere
○ Probably contained CO2, CO, Nitrogen, Ammonia,
Methane
○ But, No Oxygen! (wouldn’t support life)
◍ 3.8 BYA
○ Earth cooled enough for liquid water to
form
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7. When did Life Began?
◍ 4.28 BYA
○ Fossils (microfossils) discovered in
hydrothermal vent precipitates
◍ 3.5 BYA
○ Life on Earth initially began with prokaryotes,
discovered in sedimentary rock formations called
stromatolites.
◍ Prokaryotes – cells that do not have
Nucleus (Bacteria and Archea) 7

8. Going back…
◍ Early Atmosphere
○ Probably contained CO2, CO, Nitrogen, Ammonia,
Methane
○ But, No Oxygen! (wouldn’t support life)
◍ Anaerobic organism – capable of
surviving without oxygen
◍ 3.0 BYA - The first photosynthetic
organism thrived the earth which is blue
green algae called cyanobacteria. 8

9. The Earth’s Timeline
◍ Unicellular organisms >> Multicellular
Organism
◍ 2.0 BYA - Appearance of the first
eukaryotes and the influx of
multicellular organisms occurred 1.2
billion years ago.
○ Eukaryotes – multicellular, with true nucleus
○ The first eukaryotes were protists
◍ Evolution play a pivotal role
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11. The Earth’s timeline
◍ 500 MYA The Paleozoic era when the
trilobites and cephalopods became
dominant in the ocean particularly
during the
Cambrian and Ordovician
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12. 251 to 65.5 MYA
◍ The Mesozoic era-the age of reptiles
that has a span of 251 to 65.5 MYA
divided into Triassic, Jurassic and
Cretaceous period
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14. ◍ 250 TYA
◍ The Cenozoic era- recent life and based
on paleontological evidence. Homo
erectus have evolved.
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15. “
THE CONCEPT OF WHEN IS
ALWAYS DEBATABLE
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16. “
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D
B
A
C
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18. THEORIES ON THE
ORIGIN OF LIFE

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22. THEORIES ON THE ORIGIN OF LIFE
◍ DIVINE CREATION
○ Life is created by a Supreme Being.
◍ ABIOGENESIS THEORY (SPONTANEOUS
GENERATION)
○ Life could appear from non-living material
◍ BIOGENESIS THEORY
○ Life could appear from living material
◍ PANSPERMIA THEORY
○ Extraterrestrial Origin
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23. Theory of Biochemical Evolution
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24. Classical Experiments
on Evolution of Life

25. “
Why is it important to falsify or
verify a claim through an
Experiment?
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26. “
Spontaneous Generation
(Abiogenesis)- The hypothesis
that life arises regularly from
non-living thing
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28. Biogenesis Theory
Life could appear from living material
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29. Classical Experiments on Evolution of
Life
Italian physician and poet, Francesco Redi
(1668)
◍ Hypothesis: Maggots arose from tiny,
non-visible eggs laid on meat
◍ Procedures:
○ Put pieces of meat in several jars, leaving half
open to the air
○ Cover the other half with thin gauze to prevent
entrance of flies
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30. Classical Experiments on Evolution of
Life
◍ Results:
After a few days, meat in all jars
spoiled and maggots were found
only on the meat in the uncovered
jars
One of the first documented
experiments to use a control!
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31. Classical Experiments on Evolution of
Life
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32. Classical Experiments on Evolution of
Life
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33. Classical Experiments on Evolution of
Life
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34. Classical Experiments on Evolution of
Life
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35. Classical Experiments on Evolution of
Life
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36. Classical Experiments on Evolution of
Life
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37. Classical Experiments on Evolution of
Life
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38. Classical Experiments on Evolution of
Life
◍ French scientist, Louis Pasteur (1859)
○ The French Academy of Sciences held a contest for the best
experiment either proving or disproving spontaneous generation
◍ Hypothesis: Microorganisms do not arise from meat
broth
◍ Procedures:
○ Place meat broth in a flask with a long, curved neck. (This permitted
air to enter, but trapped dust and other airborne particles)
○ Boil the flask thoroughly to kill any microorganisms
○ Do NOT seal the open end of the flask
○ Wait an entire year before gathering results 38

39. Classical Experiments on Evolution of
Life
◍ Results:
○ After a year, no microorganisms could be
found in the broth!
○ Pasteur then removed the curved neck,
permitting dust and other particles to
enter. In just one day, the flask contained
microorganisms!
○ Microorganisms had clearly entered the
flask with the dust particles from the air
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41. thanks!
Any questions?
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