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General Biology 2
Quarter 3-Module 2:
History of Life on Earth

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General Biology 2 – Grade 12
Quarter 3– Module 2: History of Life on Earth

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Published by the Department of Education

Secretary: Leonor Magtolis Briones
Undersecretary: Diosdado M. San Antonio

Development Team of the Module

Compiler/Writer: Ms. Cristina C. Genosa
Editors/Reviewers: Ms. Celia C. Gepitulan
Mrs. Jocelyn C. Butanas
Mr. Bonnie James A. Saclolo
Language Editor: Mrs. Roquesa B. Sabejon

Management Team: Dr. Rhea Mar A. Angtud

Schools Division Superintendent
Dr. Bernadette A. Susvilla
Assistant Schools Division Superintendent
Dr. Grecia F. Bataluna
Chief, Curriculum Instruction Division
Dr. Luis O. Derasin, Jr.
EPS-Aral. Pan./SHS Division Coordinator
Mrs. Vanessa L. Harayo, LLB.
Division EPS In-Charge of LRMS
Mrs. Raylene S. Manawatao
EPS, Science

Department of Education – Schools Division of Cebu City, Region VII

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 MODULE 2
History of Life on Earth
Quarter : Third Quarter
Content Standard : The learners demonstrate an understanding of the
history of life on Earth.
Performance Standard : The learners should be able to illustrate through a
diagram the sequence of the geologic time scale and the
major groups of organisms present during these time
periods.
Learning Competency : Describe general features of the history of life on
Earth, including generally accepted dates and sequence
of the geologic time scale and characteristics of major
groups of organisms present during these time periods
(STEM_BIO11/12-IIIc-g-8)
Duration : 1 Week
Topic : History of Life on Earth

Hello STEM learners!

In this module, you will travel back in time to revisit the beginnings of life
on Earth and discover the major groups of organisms that represented the
periods in the geologic time scale. You will also learn about the events that lead
to the diversity of organisms and the extinctions of major group of organisms.
The module is divided into two lessons, namely:
Lesson 1—The Precambrian Supereon
Lesson 2—The Phanerozoic Eon

After going through this module, you are expected to:

1. distinguish between eons, eras, periods, and epochs;
2. describe the characteristics of the major groups of organisms present
during the periods of the geologic time scale;
3. illustrate through a diagram the sequence of events of the geologic time
scale;
4. identify the major mass extinctions that happened in the past and
determine their roles in the diversification of life in the present Earth;
5. appreciate the contributions of geology in the development of the
geologic time scale.

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Direction: Write the letter of the correct answer on a separate sheet of paper.

1. Which geologic era is known as the "Age of Invertebrates”?

A. Cenozoic C. Paleozoic
B. Mesozoic D. Proterozoic
2. Which of the following represents the longest time?
A. Cenozoic C. Phanerozoic
B. Mesozoic D. Precambrian
3. Which of these is NOT a period of the Paleozoic Era?
A. Jurassic C. Ordovician
B. Mississippian D. Permian
4. Which geologic period is known as the "Age of Amphibians"?
A. Carboniferous C. Permian
B. Ordovician D. Silurian
5. Which geologic era is known as the "Age of Mammals"?
A. Cenozoic C. Paleozoic
B. Mesozoic D. Proterozoic
6. Which of these eras was dominated by dinosaurs?
A. Cenozoic C. Paleozoic
B. Mesozoic D. Proterozoic
7. When did the first true mammals first appear?
A. Triassic period C. Paleogene period
B. Jurassic period D. Cretaceous period
8. Which geologic period ended the reign of the dinosaurs?
A. Cretaceous B. Jurassic C. Paleogene D. Permian
9. Which geologic period did the "mother of mass extinctions" occur, wiping out
more than 90% of species?
A. Cretaceous B. Devonian C. Ordovician D. Permian
10. Which geologic period did most of the coal beds form which is the main
source of the fossil fuel we have today?
A. Cambrian C. Cretaceous
B. Carboniferous D. Permian
11. What is age of the oldest fossil of the first eukaryote?
A. 1.2 byo B. 1.6 byo C. 3.8 byo D. 4.6 byo
12. Which dating method can provide geologists with the exact age in years of
rocks, fossils, and other ancient materials on Earth?
A. Relative dating C. Fossil Succession
B. Absolute dating D. All of the given.
13. How many mass extinction events were recorded in the geologic time scale?
A. 2 B. 3 C. 4 D. 5
14. Which geologic era is known as the "Age of Reptiles"?
A. Cenozoic C. Paleozoic
B. Mesozoic D. Proterozoic
15. When did the first modern human beings appear?
A. Holocene B. Miocene C. Pleistocene D. Pliocene

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 Introduction: Geology and the Geologic Time Scale

The science that deals with studying the Earth—its materials and
processes is known as geology. Modern geology began in late 1700s when James
Hutton introduced the Principle of Uniformitarianism, which became the
fundamental principle of geology today. The principle states that forces and
processes that can be observed shaping the Earth at present, have been at work
for a long time since the Earth’s beginnings. Many of the important contributions
in the advancement of geology began with the study of rocks and its layering
(strata). Ancient rocks have unlocked various types of evidences of ancient lives
that have been hidden for millions, even billions of years. Today, scientists like
geologists, paleontologists (scientist who study fossils), chemists, and biologists
have worked together to analyze the physical, chemical, and biological materials
in ancient rocks. Geologists use the principles of relative dating and the
principle of fossil (remains of dead organisms) succession in determining the
age of rocks, which became the start of the development of the geologic timescale,
a scale that can place rock evidence into specific time interval and recreate the
events of the past to the present time. These methods were limited at comparing
the relative age (older vs younger) of the layers of rocks and comparing rock
layers with layers from other locations.

The discovery of radioactive isotopes in rocks and the hidden materials

within it, allowed chemists to introduce an absolute dating method that uses
these radioactive isotopes to determine the exact age (in years) of rocks, fossils,
and other materials. This method is also known as radiometric dating and
together with relative dating methods have allowed geologists to retell the history
of the Earth and most importantly, the history of life on Earth, in the geologic
time scale. It is important to remember that several evidences are still being
unearthed even up to now and so, we must understand that the geologic time
scale is still a work in progress.

Let us review.
Direction: Answer the following items on a separate sheet of paper.
1. Differentiate the following terms:
a) Geology vs Paleontology-

b) Relative age vs Absolute age-

2. What is the importance of fossils in the construction of the geologic time

scale?
_______________________________________________________________________

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The Geologic Time Scale

The geologic time scale divides the history of the Earth into time intervals
which are: eons, eras, periods, and epochs. The longest time interval is eon
which can be subdivided into smaller intervals called eras, and eras can be
divided into periods, and periods into much smaller intervals called epochs. The
geologic time scale gets the formal names based on rock evidence (which may
include fossils and other chemical evidence) that is date specific. The
International Committee on Stratigraphy (ICS), a committee of the
International Union of Geological Sciences are responsible for determining and
formalizing the time intervals of the Geologic Time Scale.

Figure 2.1. The Geologic Time Scale

As you can see in figure 2.1, the geologic time scale is divided into the
Precambrian supereon and Phanerozoic eon. The Precambrian supereon is an
informal name for the longest time interval which represents about 88% of the
Earth history which began 4.6 billion years ago (bya). This time interval is
divided into the Hadean (informal name) eon, Archean eon, and Proterozoic eon.
Informal names are names given to the earliest time intervals where no available
details or evidence exist, these times are uncertain but are otherwise given
informal names to represent them.

The Phanerozoic eon is the time interval that began 541 million years ago
(mya) and is derived from Greek words meaning “visible life”, which is
appropriate as this eon represents a large collection of evidences of diverse life
forms that showed major evolutionary transitions.

Let us review.
Direction: Answer the following items on a separate sheet of paper.
1. Arrange the following time intervals from the longest (4) to the shortest (1)
time interval.
a) Eon _____
b) Epoch _____
c) Era _____
d) Period _____

2. Study figure 2.1, how long (in years) did the Precambrian supereon happen
before the Phanerozoic eon started? (Use your Math skills to answer the
question.) Hint: 1 billion years=1,000 million years
_______________________________________________________________________

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 Lesson 1: The Precambrian Supereon

Archean eon
The Archean eon is said to be the time when first signs of life began. The
oldest rock known is found in an area of Greenland called the Isua formation
which is about 3.85 billion years old. These rocks contain quartz crystals that
preserved organic deposits of carbon isotopes which are found in organisms.
This finding showed a glimpse of the first simple organisms that lived in this
eon. They did not use oxygen but used organic molecules that formed near the
end of the Hadean eon, which became sources of carbon and energy. Carbon
dioxide was also said to be abundant in the atmosphere during the Archean eon.
Then, after millions of years, organisms started to evolve and utilize light energy
and atmospheric CO2 for photosynthesis. These organisms were known as
photosynthetic bacteria and archea, thus, the term Archean eon for the
dominant groups of bacteria (classified as prokaryotes) that are able to survive
in extreme environment.

By that time, the Earth’s atmosphere changed dramatically becoming rich

with oxygen gas. Many of the organisms were believed to have died due to the
presence of oxygen which was toxic for them. But, for those able to evolve and
utilize oxygen gas, gave rise to the aerobic organisms. This evolution of simple
anaerobic to aerobic organisms went on for millions of years. Evidence of the
oldest known fossils were about 3.7 billion years old in rocks found in Australia
and South Africa which resembled the huge formations of cyanobacteria called
stromatolites. The massive oxygenation event in the Archean eon can be
evidenced by the extensive iron deposits in layers of sedimentary rocks dated
2.0 bya. The iron which were said to be previously dissolved in the oceans
reacted with dissolved O2 in the oceans, these created a rusty colored layering
in these rock sediments.

Proterozoic eon
After the prokaryotes dominated the archean eon, the rise of the
eukaryotes (unicellular organisms with true nucleus) followed. Fossil evidence
show that eukaryotes emerged about 1.9 to 1.4 bya. Recorded fossils from
Australia dated 1.69 byo are chemically similar to eukaryotic membranes. The
evolution of eukaryotes can be explained in the Endosymbiotic Theory
proposed by Lynn Margulis.

In another million years after the eukaryotes evolved, the multicellular

organisms arose which is said to have occurred 1.2 bya. The earliest fossil
evidence of multicellular organisms are from the red alga dated about 1.25 bya
to 950 million years ago (mya) in Canada and abundant fossils are also found in
eastern Russia dated 1.0 bya.

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 For many millions of years, unicellular (prokaryotes and eukaryotes) and
multicellular organisms evolved while some became extinct due to many events
that shaped the Earth. The events that we have been experiencing at present are
similar events that have shaped the Earth in the past, these are important events
that have allowed organisms to evolve. While many became extinct during these
events, it paved the way for new organisms to flourish.

Did you know…

Did you know that the suffix -zoic found in the names of the events in the
geologic time scale refer to animal life forms? This means that animal life forms
were dominant during these events.

Comparing Fossil Evidence in the Precambrian supereon

Direction: Copy the table below. Put a check ( ) mark under the column of the
eon if the identified fossil evidence dates to that eon.
Fossil evidence Archean Proterozoic
1. red alga (1.25 bya)
2. quartz crystals containing organic deposits (3.85
bya)
3. huge formations of cyanobacteria called
stromatolite (3.7 bya)
4. fossils containing similar chemical components of
eukaryotic membranes (1.69 bya)
5. iron-containing sediments (2.0 bya)

Direction: To check your understanding of the concepts in lesson 1, fill in the

appropriate term/s to complete the statements below. Write your answers
immediately on a separate paper.
In this module, I have learned that…
1. The _______________________ is a tool that geologists use to subdivide the
history of the Earth into events.
2. The geologic events are subdivided into time intervals which include
______, eras, ______, and ______.
3. The longest time interval (formal) is an _______ and the shortest (in our
notes) is an _______.
4. To construct the geologic time scale, geologists rely on two methods to
determine the age or date of the layers of rocks, these are _____________and
____________ dating.

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 5. The major part or 88% of the Earth’s history is identified as the
_________________ supereon.
6. The most recent eon is referred to as the ____________________ eon.
7. Geologists subdivided the Precambrian supereon into the _____________
(informal name), ________________, and _______________ eons.
8. The Hadean eon is estimated to have started ____________ billion years ago
(bya), which said to be the age of the Earth.
9. The single-celled organisms, also known as __________________ organisms,
first appeared in the Archean eon which were mostly anaerobic bacteria.
10. By the end of the Proterozoic eon, _________________ organisms arose 1.25
bya, which is evidenced by fossils of the ancient red alga found in Canada.

Illustrating the Precambrian Supereon

Instructions
1. On a separate bond paper draw either one of the eons of the Precambrian
supereon to illustrate the kind of landscape and organisms that may have
dominated during that time.
2. Include the most significant things that can be used to describe that eon
and label them. Use any type coloring materials for your illustration. (Refer
to the rubric for the illustrations.)
3. Answer the review questions that follow.

Rubrics for the Illustrations

CATEGORY 4 3 2 1
Presentation The drawing The drawing The drawing
The drawing clearly communicates indirectly does not
communicates the some of the communicates sufficiently
main idea and important ideas the idea and communicate
strongly promotes and slightly hardly promotes any idea that
awareness. promotes awareness. can promote
awareness. awareness.
Creativity and All of the graphics Most of the The graphics The graphics
Originality used on the drawing graphics used on were made by the were not made
reflect an exceptional the drawing student but were by the student.
degree of student reflect student copied from the
ingenuity in their ingenuity in their designs or ideas
creation. creation. of others.

Accuracy and Most graphics in Some graphics in The graphics in

All graphics in the
Relevance of the the drawing are the drawing are the drawing are
drawing are accurate
Content accurate and accurate and neither accurate
and related to the
related to the related to the nor related to
topic.
topic. topic. the topic.
Required The drawing All required Few required Required
Elements includes all required elements are elements are elements are
elements as well as included. included. missing.
additional
information.

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Let us review.

Direction: After reading the materials in the previous pages, briefly answer the
questions below. Write answers on a separate sheet of paper.

1. Based on the evidence collected by scientists, how old is the present

Earth? ________________________________________________________________
2. Do you think that living organisms could have survived the Hadean eon?
Explain your answer.___________________________________________________
3. What are the most significant differences between the Archean and
Proterozoic eons? ______________________________________________________

Lesson 2: The Phanerozoic Eon

The geologic time scale is divided into the Precambrian supereon and the
Phanerozoic eon.

Let us review.

Direction: Fill in the names of the events in the figure below. Write answers on
a separate paper.

Figure 2.2 The Geologic Time Scale—Label the Events.

The Phanerozoic eon is the more recent eon and is subdivided into eras
which include Paleozoic era, Mesozoic era, and Cenozoic era (shown in figure
2.3). These eras are further subdivided into periods and the most recent periods
are subdivided into shorter time intervals called epochs. Phanerozoic is derived
from the Greek word that means “visible life” which is appropriate as this eon
represents the widest collection of small to large fossils from different organisms
that show evolutionary transitions which are found in rock layers dated from
541 mya to present.

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 Figure 2.3. Geologic Time Scale- Phanerozoic Eon

In the following section, we will know more about the subdivisions of the
phanerozoic eon.

Paleozoic Era (“Age of Invertebrates”)—541-252 mya

The Paleozoic Era represents the time of the “ancient life” which was
dominated by ancient marine invertebrates. Paleozoic era is subdivided into six
periods namely: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and
Permian, arranged in sequential events from the oldest to the more recent event.
The subdivisions are represented in figure 2.4.

Figure 2.4. Geologic Time Scale- Paleozoic Era

Cambrian Period
This period is also known as “Cambrian explosion” as fossils of major
groups of animals diversified within a few million years of each other. Most
important fossils were from organisms with hard parts including the insect-like
trilobites, nautiloids, scorpion-like eurypterids, and brachiopods, which looked
like clams. Many of these invertebrates were identified only as “small, shelly
fossils” and coexisted with the abundant red and green algae, sponges,
jellyfishes, and worms which were found in the Cambrian seas.

Ordovician Period
Fossil evidence of the first vertebrates, jawless fishes called ostracoderms,
appeared during this period. Fossil evidence also showed that spore-forming
primitive plants (resembled nonvascular plants today) may have moved to land.
The Ordovician period ended with a large-scale mass extinction of marine
invertebrates.

Silurian Period
The first plants with water-conducting and mineral conducting tissues
known as vascular plants evolved at this time. The first land animals also left
fossil evidence which looked like scorpions which were predators of smaller
animals. Fungi are said to have also colonized land. Aquatic animals also
continued to diversify which is very common after a mass extinction event.

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Varied forms of fishes (jawless and jawed) lived in freshwater and marine
environments, the oceans were rich in corals, trilobites and mollusks.

Devonian Period
This period is known as the “age of fishes” as more fishes diversified as
bony and cartilaginous fishes. By the end of the period, the first amphibian
appeared which resembled fishes but with paddlelike legs and toes. Mass
extinction of marine organisms ended the Devonian period, although many land-
dwelling organisms, such as the highly diversified plants, were mostly not
affected.

Carboniferous Period
This period is known as the “age of amphibians” as more amphibians
dominated both land and water. The carboniferous period is subdivided into two
epochs, namely (oldest to more recent): Mississippian and Pennsylvanian.
Many land plants like ferns and early seed plants and many different kinds of
insects dominated the Carboniferous (meaning “coal bearing”) period. By the end
of the period, many of these plants died which were buried beneath swamps
which formed the rich coal layers of the Earth, which is the source of the fossil
fuel (coal) that we have today.

Permian Period
During this period, gymnosperms (non-flower bearing plants) became
dominant while reptiles were the dominant animals including the ancestors of
dinosaurs. The Permian period ended with the most catastrophic mass
extinctions, also known as “the mother of mass extinctions,” as it affected 90%
of species, which were mostly marine invertebrates found in shallow areas of the
seas.
Mesozoic Era (“Age of Reptiles”)—252-66 mya
The Mesozoic was dominated by small and huge reptiles called the
dinosaurs. This era is subdivided into three periods, namely: Triassic, Jurassic,
and Cretaceous periods (shown in figure 2.5).

Figure 2.5. Geologic Time Scale- Mesozoic Era

Triassic Period
The ancestors of the now-extinct dinosaurs called the archosaurs
increased during this period paving the way of the “age of reptiles”. The ancestors
of mammals called therapsids also appeared and coexisted with the reptiles in
the forested lands. Forests were mainly dominated by gymnosperms such as
cycads, ginkgos, and conifers. Another mass extinction occurred by the end of
the Triassic period affecting smaller reptiles, amphibians, and marine animals.
The larger, more adapted reptiles dominated the land which included the
dinosaurs.

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Jurassic Period
This period is known as the “age of dinosaurs” as this was dominated by
them. Both herbivorous and carnivorous reptiles dominated the land, including
large marine crocodiles, the ancestors of birds (Archeopteryx) and dinosaurs. The
first flowering plants (angiosperms) appeared during this period, but forests were
still dominated by gymnosperms. The first frogs and the first true mammals,
which were the size of rats, appeared at this time.
Cretaceous Period
Huge diversification of organisms both plants and animals occurred at this
time. Flowering plants diversified so fast, and many insects also appeared.
Reptiles hunting other groups of animals and even those of their own was very
common at this time. The Cretaceous period ended with the mass extinction of
75% of species including the large reptiles, the dinosaurs, and thus, ending the
Mesozoic era. The mass extinction cleared the way for the dominance of smaller
organisms that survived the asteroid impact (said to be the cause of the mass
extinction) which included the birds, amphibians, and mammals.

Cenozoic Era (“Age of Mammals”)—66 mya-present

The Cenozoic era is the most recent era and has been dominated by the
greatly diversified mammals. This era is subdivided into three periods, namely:
Paleogene, Neogene, and Quaternary periods (as shown in figure 2.6).

Figure 2.6. Geologic Time Scale-Cenozoic Era

Paleogene Period
Subdivided into three epochs:
• Paleocene epoch—early placental mammals appeared including
the first primates, speciation of birds and insects.
• Eocene epoch—angiosperms dominated, origin of the mammalian
orders including the appearance of the primitive whales.
• Oligocene epoch—origins of the different primate groups including
the apes; tropical rainforests appeared in many continents; pigs,
cats and rhinos appeared; marine life was dominated by mollusks.

Neogene Period
Subdivided into two epochs:
• Miocene epoch—coevolution of angiosperms and insects;
continued speciation of mammals.
• Pliocene epoch—origin of the hominids (Homo)

Quaternary Period (most recent)

Subdivided into two epochs:
• Pleistocene epoch—origin of modern humans; major glaciation
events occurred (ice ages)

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Did you know…

Did you know that the oldest fossils ever recorded in the Philippines dates
back between 777 to 631 thousand years ago (tya) during the Pleistocene epoch?
These findings were discovered in Kalinga, Cagayan Valley of northern Luzon. It
included remains of rhinoceros, stegodon, brown deer, and early hominins yet
to be identified. The most recent identified hominin is Homo luzonensis or Callao
Man dated 67 tya which was found in Callao Cave, Peñablanca, Cagayan by
Armand Mijares and his team from the University of the Philippines.

• Holocene epoch—rise of human civilization, impact of human

activities are widespread and continues to the present time

Did you know…

Did you know that many scientist think that we are now in a new epoch
called the Anthropocene which is marked by extensive human impacts to the
environment? Geologists use markers in the rock strata to determine the end
and beginning of a time in the goelogic time scale, the anthropocene is marked
by road buildings, microplastics, pollutants, extinctions of species, greenhouse
gases and many more wastes found since the beginning of the industrial
revolution or globalization in the 1950s.

Features of the Phanerozoic Eon

Direction: Copy the table below. Put a check ( ) mark under the column which
best fits the description given in the first column from the left.
Description Cenozoic Mesozoic Paleozoic
1. “Age of Mammals”
2. “Age of Reptiles”
3. “Age of Invertebrates”
4. Marked by time of the Cambrian
explosion and the “mother of mass
extinctions”
5. The longest era, so far, in the
phanerozoic eon.
6. Marked by the dominance and
extinction of dinosaurs
7. Marked by the rise and dominance of
humans and other mammals.

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Direction: To check your understanding of the concepts in lesson 2, fill in the
appropriate term/s to complete the statements below. Write your answers on a
separate sheet of paper.
In this module, I have learned that…
1. The _______________________ eon is the more recent eon in the geologic time
scale. This eon is subdivided into: ___________, Mesozoic, and __________
eras.
2. The __________________ era is referred to as the era of “ancient life” which
was mostly dominated by marine ____________________.
3. The __________________ era is referred to as the “middle life” era as this was
in the middle of the phanerozoic eon.
4. The Cenozoic era is subdivided into three periods, they are:
_______________, __________________, and Quaternary.
5. The ____________________ epoch is said to be the time when human
civilizations rose, and human activities changed the face of the Earth.

Illustrating the Phanerozoic Eon

Instructions
1. On a separate bond paper draw either one of the eras of the Phanerozoic
eon to illustrate the kind of landscape and organisms that may have
dominated during that time.
2. Include the most significant things that can be used to describe that eon
and label them. Use any type coloring materials for your illustration. (Refer
to the rubric for the illustrations on page 9 of this module.)
3. Answer the review questions that follow.

Let us review.
Direction: After reading the materials in the previous pages, briefly answer the
questions below on a separate sheet of paper.
1. How many mass extinctions have been identified in the Phanerozoic eon?
Please identify them. __________________________________________________
2. What is the significance of mass extinctions in the history of life on Earth?
_______________________________________________________________________
3. How do you differentiate the events of the Phanerozoic eon from the
Precambrian supereon? Give three sentences.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________

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Direction: Write the letter of the correct answer on a separate sheet of paper.
1. Which of the following is the SECOND event in the geologic time scale?
A. Eukaryotes arose. C. First multicellular organisms arose.
B. Prokaryotes arose. D. O2 accumulated in the atmosphere.
2. Which of the following represents 88% of the Earth history?
A. Cenozoic era C. Phanerozoic eon
B. Mesozoic era D. Precambrian supereon
3. How did the photosynthetic organisms affect the early Earth?
A. They depleted the ozone layer.
B. They added O2 in the atmosphere.
C. They introduced the greenhouse gases into the atmosphere.
D. They increased the amount of hydrogen sulfide in the early ocean.
4. Which of the following represents the correct order of appearance, from the
earliest to the most recent group of organisms in the geologic time scale?
A. Ferns, humans, dinosaurs, mammals
B. Fishes, reptiles, seed plants, trilobites
C. Reptiles, fishes, angiosperms, amphibians
D. Ancient red alga, invertebrates, fishes, gymnosperms
5. Which dating method can provide geologists of the age in years of rocks,
fossils, and other ancient materials of the Earth?
A. Relative dating C. Fossil Succession
B. Absolute dating D. All of the given
6. How many mass extinction events were recorded in the geologic time scale?
A. 2 B. 3 C. 4 D. 5
7. When did the "mother of mass extinctions" occur, wiping out more than 90%
of species?
A. Cretaceous period C. Ordovician period
B. Devonian period D. Permian period
8. Which of these is NOT a period of the Paleozoic Era?
A. Carboniferous C. Jurassic
B. Ordovician D. Permian
9. Which of these bests describes the Mesozoic era?
A. Mass extinctions of dinosaurs and large reptiles ended the Mesozoic
era.
B. It was an era marked by the domination of reptiles and flowering
plants.
C. This era is subdivided into the Triassic, Jurassic, and Cretaceous
periods.
D. All of the above.

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10. Which of these bests describes the Archean and the Proterozoic eons?
A. Both eons are subdivisions of the Phanerozoic supereon.
B. No life is possible during these eons because the Earth was still
inhospitable to living organisms.
C. Both eons provided the timeline for simple organisms (both prokaryotes
and eukaryotes) to evolve to give rise to the multicellular organisms
which eventually lead to the diversity of life-forms we have today.
D. All of the above.
11. When did most of the coal beds form which is the main source of the fossil
fuel we have today?
A. Permian period C. Cretaceous period
B. Cambrian period D. Carboniferous period
12. What is the oldest recorded fossil?
A. Fossils of trilobites
B. Ancient red alga found in Canada.
C. Microfossils of cyanobacteria called stromatolites.
D. Fossils that contain similar chemical signatures as eukaryotic
membranes
13. How old is the oldest recorded fossil that is said to be the evidence of the first
eukaryote?
A. 1.2 byo B. 1.6 byo C. 3.8 byo D. 4.6 byo
14. Which of these bests describes the Cenozoic era? It is/was ___________.
A. dominated by small and huge reptiles called the dinosaurs.
B. dominated by marine invertebrates which included the Cambrian
explosion.
C. the most recent era and has been dominated greatly by the diversified
mammals.
D. largely populated by simple-celled organisms that evolved to become
the first photosynthetic organisms.
15. Modern human beings appeared during which geologic period?
A. Miocene C. Holocene
B. Pliocene D. Pleistocene

17
REFERENCES
Offline sources
Hoefnagels, Marielle. Biology: Concepts and Investigations. New York: McGraw-
Hill Education, 2018.

Lutgens, Frederick K., Edward J. Tarbuck, and Dennis Tasa. Foundations of

Earth Science. Boston: Pearson, 2017.

Urry, Lisa A., Michael L. Cain, Steven Alexander Wasserman, Peter V. Minorsky,
Rebecca B. Orr, and Neil A. Campbell. Campbell Biology. New York, NY:
Pearson, 2020.

Online sources
Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) The ICS
International Chronostratigraphic Chart. Episodes 36: 199-204. URL:
http://www.stratigraphy.org/ICSchart/ChronostratChart2020-03.pdf.

Greshko, Michael, and Maya Wei-Haas. “New Species of Ancient Human

Discovered in the Philippines.” Science. National Geographic, February 10,
2021. https://www.nationalgeographic.com/science/article/new-species-
ancient-human-discovered-luzon-philippines-homo-
luzonensis#:~:text=Humankind's%20tangled%20shrub%20of%20ancestry,
50%2C000%20to%2067%2C000%20years%20ago.

Ingicco, T., G. D. van den Bergh, C. Jago-on, J.-J. Bahain, M. G. Chacón, N.

Amano, H. Forestier, et al. “Earliest Known Hominin Activity in the
Philippines by 709 Thousand Years Ago.” Nature News. Nature Publishing
Group, May 2, 2018. https://www.nature.com/articles/s41586-018-0072-
8.

Geologic time scale. Accessed March 8, 2021.

https://ucmp.berkeley.edu/help/timeform.php.

“EarthViewer.” HHMI BioInteractive, October 16, 2017.

https://www.biointeractive.org/classroom-resources/earthviewer.

“The Anthropocene: Human Impact on the Environment.” HHMI BioInteractive,

January 7, 2019. https://www.biointeractive.org/classroom-
resources/anthropocene-human-impact-environment.

“The Making of Mass Extinctions.” HHMI BioInteractive, January 13, 2016.

https://www.biointeractive.org/classroom-resources/making-mass-
extinctions-0.

18
 19
What’s More
Comparing Fossil Evidence in the Precambrian supereon
Put a check ( ) mark under the column of the eon if the identified fossil evidence dates
back to that eon.
Fossil evidence Archean Proterozoic
1. red alga (1.25 bya)
2. quartz crystals containing organic deposits (3.85 bya)
3. huge formations of cyanobacteria called stromatolite
(3.7 bya)
4. fossils containing similar chemical components of
eukaryotic membranes (1.69 bya)
5. iron-containing sediments (2.0 bya)
What’s New
Let us review.
1. a) Eon 4
b) Epoch 1
c) Era 3
d) Period 2
2. Hint: 1 billion years= 1,000 million years
Beginning of Precambrian supereon →4.6 bya=____mya
4.6 bya x 1,000 mya = 4,600 mya
1 bya
Beginning of Phanerozoic and end of Precambrain supereon→ 541mya
4,600 mya – 541 mya = 4,059 mya or 4.059 bya (the length of the Precambrian supereon
before Phanerozoic started)
What’s In
Let us review.
1. a) Geology is the science that deals with studying the Earth’s materials and processes while
paleontology is the science that deals with the study of fossils and remains of living
organisms.
b) Relative age is used to determine which rock layer is older or younger than the other
layers while the absolute age is very specific in number of years, also known as numerical
age.
2. Fossils are used in the study of fossil succession in layers of rocks and are used in relative
dating.
Lesson 1
 20
What’s More
Features of the Phanerozoic Eon
Put a check ( ) mark under the column (era) which best fits the description given in the
first column from the left.
Description Cenozoic Mesozoic Paleozoic
1. “Age of Mammals”
2. “Age of Reptiles”
3. “Age of Invertebrates”
4. Marked by time of the Cambrian explosion and
the “mother of mass extinctions”
5. The longest era, so far, in the phanerozoic eon.
6. Marked by the dominance and extinction of
dinosaurs
7. Marked by the rise and dominance of humans
and other mammals.
What’s In
Let us review.
1. Precambrian supereon
2. Phanerozoic eon
3. Hadean eon
4. Archean eon
5. Proterozoic eon
Lesson 2
What I Can Do
Let us review. (Suggested answers)
1. The Earth 4.6 byo.
2. No. Much of the Earth was still either too hot or requirements to support life were still not
formed. Many scientists relied on data from observations on other planets to illustrate how
difficult it was for organisms to have survived with the kind of environment the Hadean eon
had.
3. Archean eon was the time that prokaryotes dominated and contributed to changing the
conditions of the Earth. Such conditions made possible the evolution of more complex
organisms in the Proterozoic eon which began the appearance of more complex organisms
such as the red alga.
What I Have Learned
In this module, I have learned that…
1. geologic time scale
2. eons, period, epochs
3. eon, epoch
4. relative, absolute
5. Precambrian
6. Phanerozoic
7. Hadean, Archean, Proterozoic
8. 4.6
9. unicellular
10. multicellular
 21
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Telefax: (632) 8634-1072; 8634-1054; 8631-4985
Meralco Avenue, Pasig City, Philippines 1600
Ground Floor, Bonifacio Bldg., DepEd Complex
(DepEd-BLR)
Department of Education - Bureau of Learning Resources
For inquiries or feedback, please write or call:
What I Can Do
Let us review. (Suggested answers)
1. There were five mass extinctions. These were:
2. Mass extinctions may have killed many species, but it has allowed the less dominant
species to flourish and diversify. Diversification through the mechanisms of evolution,
always follows mass extinctions.
3. Phanerozoic eon involved the great diversification of animals and plants which happened
because the Precambrian supereon provided the means for start-up. All pre-requisite
conditions for larger, complex organisms have been laid down by their unicellular
ancestors. Precambrian took the longest time to make the Earth habitable and soon,
animals in the Phanerozoic diversified, filling the Earth with life.
What I Have Learned
In this module, I have learned that…
1. Phanerozoic; Paleozoic, Cenozoic
2. Paleozoic; invertebrates
3. Mesozoic
4. Paleogene, Neogene
5. Holocene