2 1 lesson timeline of events and unifying themes in life

Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence
TIMELINE OF EVENTS (Appearance of Life Forms)
4.6 – 3.8 BYA (BILLION YEARS AGO) = The early earth is said to be violent because of the meteorites
and volcanic eruptions. With this condition, zircon crystal was formed.
3.5 BYA = Life on Earth initially began with prokaryotes, discovered in sedimentary rock formations
called stromatolites.
3.0 BYA = The first photosynthetic organism thrived the earth which is blue green algae called
2.0 BYA = Appearance of the first eukaryotes and the influx of multicellular organisms occurred 1.2
billion years ago.
500 MYA = The Paleozoic era when the trilobites and cephalopods became dominant in the ocean
particularly during the Cambrian and Ordovician.
251 MYA – 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.
250 TYA = The Cenozoic era- recent life and based on paleontological evidence. Homo erectus have


(Early Earth

(Period of
Apperance of first

(Recent Life)

(Dominance of

(Period of
apperance of the
first eukaryote)

(Dominance of
appearnce of

The universe is about 4.6 billion years old. Life on earth, probably began only between 3.5 and 4.0
billion years ago. Evidence from fossil records show the emergence of the different life forms. The
common ancestor of all life was prokaryotic.
Since, oxygen was scarce on the early Earth, so the ancestral cell must also have been anaerobic.
There are some challenges encountered in searching for the evidence of early life. Cells are
microscopic and most have no parts to fossilize. The tectonic plate movements have destroyed
nearly all rocks older than about 4 billion years, and most of the younger rocks have been heated or
undergone processes that destroy the traces of biological material. At present, the oldest cell
microfossils (microscopic fossils) are filaments from 3.5 billion-year-old rocks in Western Australia. The
filaments resemble chains of modern photosynthetic bacteria and the rocks in which they occur are
the remains of ancient stromatolites.
The researchers look for biomarkers specific to eukaryotes. It is a substance that occurs only or
predominantly in cells of a specific type. Eukaryotes are organisms having true nucleus. The DNA is

Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence
enclosed within the nucleus whereas DNA of most prokaryotes lies enclosed in the cell’s cytoplasm.
The first eukaryotes were protists.
For life to evolve from simple single-celled organisms to many millions of species of prokaryotic
species to simple eukaryotic species to all the protists, fungi, plants, and animals, took some time. The
first life forms were very basic and this then allowed for the evolution of more complex life forms.
Eukaryotic cells evolved from prokaryotic cells. The evolution of life is brought about the changes in
the environment which are linked to changes in climate and geology. These Earth’s environmental
changes made the Earth’s environment more suitable for a wider variety of life forms.


All living things are made up of cells
Multicellular: animal cells, plant cells, human body, germ cells
Unicellular: paramecium, amoeba, bacteria, yeast
Common ancestor was prokaryotic – do not have a nucleus
o There was a scarcity of oxygen during the Early Earth’s atmosphere so the ancestral cell
must also have been anaerobic meaning capable of living without oxygen

What is the evidence to prove such statement?

Cells are microscopic ad cannot be seen through naked eye and difficult to fossilize

The Oldest Fossil Cells

The divergence that separated the two prokaryotic domains:
➢ Bacteria and archaea – occurred rarely in the history of life, and no fossils from
before this divergence have been discovered.
Paleontologists = scientists who study fossils found microscopic living cells known as microfossils
in rocks that formed 3.5 billion years ago after Earth cooled and solidified using radioisotope
dating (uses radioactive materials such as the radioactive materials such as the radioactive
components of potassium-argon)
The microfossils filaments found in Western Australia resembles chains of modern
photosynthetic bacteria and the rocks in which they occur are thought to be remains of
ancient stromatolites which are mounded, layered structure that forms in shallow sunlit water
when a mat of photosynthetic bacteria traps minerals and sediment. These stromatolites
increase in size over time as new layers from over the old. These organisms have been so
abundant 1.25 billion years ago and were common worldwide.
Many types of bacteria carry-out photosynthesis – cyanobacteria (do so by an oxygenproducing pathway)


Microfossils of cyanobacteria were among the easiest to recognize
Form of these organisms were remained the same and left chemical fossils in the form of
broken products from pigments
1st microfossil showed remains of organisms with differences in structure and characteristics
was seen 1.5 billion years ago on the rocks.
Bigger compared to bacteria and have internal membranes and thicker wall
o Marked the beginning of eukaryotic organisms on Earth


Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence
2.5 billion years ago – oxygen released by these bacteria had began to accumulate in
Earth’s air and creating a new, global selection pressure
Other species died (considered oxygen as toxic)

How do multicellular organisms evolve?

Multicellular organisms are believed to have evolved from unicellular eukaryotes
Single eukaryotic cells, just like unicellular algae, formed multicellular aggregates, through
association with another cell producing colonies.
From colonial aggregates, the organisms evolved to form multicellular organisms through cell
Protozoans, sponges, fungi came to being
Soft bodied animals were the first fossilized animals which were discovered 580 million years
The continuous process of cell specialization bought the emergence of diverse plants and
animals – including human beings
Charles Darwin said that organisms change overtime because of adaptation to their
environment to survive.

Rise of the Eukaryotes
Prokaryotic Cell

Eukaryotic Cell

pro’= pre, ‘karyon’=nucleus present

‘eu’ = true , ‘karyon’= nucleus

Originated about 3.5 billion years ago

Originated about 1.2 billion years ago

Primitive forms




Developing nucleus

True nucleus

Small in size

Larger in Size

Non-bounded membrane


Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence




The DNA (deoxyribonucleic acid) of the
prokaryotes lies on unenclosed in the cell’s
cytoplasm while the DNA of the
eukaryotes are enclosed with an
endomembrane (group of members and
organelles). The nucleus and
endomembrane system evolve when
plasma membrane of an ancestral
prokaryote folded inward

Mitochondria and Chloroplast

Mitochondria and chloroplasts resemble
bacteria in their size and shape, and they
replicate independently of the cell that
holds them. Bacteria have their own DNA
in the form of a singular chromosome and
have at least two outer membranes and
innermost membrane similar to bacterial
plasma membrane. – Chloroplast is the site
of photosynthesis.

Origin of Some Organelles


Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence

Cell Organelles



Makes protein

Golgi Apparatus

Does the packaging and processing of


Contain enzymes to help break the food

Endoplasmic Reticulum

Transports items around the cell


For water or food storage


Present in plants only; uses sunlight to
make food through photosynthesis

Cell wall

Rigid; supports the cell

Functions of Other Cell Organelles


Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence

The unifying theme connects the different subdisciplines that make biology as a science. In addition
to, the living organisms differ from non-living organisms in various aspects.
All levels of life have systems of related parts.
– A system is an organized group of interacting parts.
– A cell is a system of chemicals and processes. It is the basic unit of life.
– A body system includes organs that interact.
– An ecosystem includes living and non-living things that interact.
Structure and function are related in biology.
– Structure determines function.
– The structure is the shape of the object.
– The function is the object’s specific role.
Organisms must maintain homeostasis to survive in diverse environments.
– Homeostasis is the maintenance of constant internal conditions.
– All living organisms must live in a stable environment.
Evolution explains the unity and diversity of life.
– Evolution is the change in living things over time. The genetic makeup of a population of a species
– It accounts for both the diversity and the unity of life.
Traits are being inherited and transferred.
– The continuity of life depends on the inheritance of biological information in the form of DNA
– The genetic information is encoded in the nucleotide sequences of the DNA (Deoxyribonucleic
Organisms reproduce.
– It is necessary part of living; process of making more of one’s own kind.
Organisms are interdependent with one another.
– Organisms have evolved to live and interact with other organisms.
– Ecology deals with the interactions of living organisms with one another and their environment.
Organisms acquire and process energy.
– Living organisms use a source of energy for their metabolic activities.
– Some living organisms capture the light energy and convert it into chemical energy in food.
– Some living organisms use chemical energy stored in molecules obtained

Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence

from food.

In addition to the properties mentioned, the two additional unifying themes in the study of life include
the scientific inquiry and science, technology and society.
Scientific Inquiry
– The process of science includes observation-based discovery and the testing of explanations
through the hypothetic-deductive.
– Scientific credibility depends on the repeatability of observation and experiments.
Science, Technology and Society
– Many technologies are goal-oriented applications of science.
– The relationships of science and technology to society are now more crucial to understand than
ever before.
Characteristics of Life
Life Characteristic



Growth and Development



Living things are able to respond to the
environment through a stimulus.
Irritability is an example. Another example is a
living thing’s response to light by facing the sun
and sweating as our body response to heat
which is also connected to excretion.
Unicellular organisms reproduce by DNA
replication and dividing equally as the new cell
prepares to form two new cells while
multicellular organisms often reproduce using its
gametes to form new individuals. When there is
reproduction, genes with DNA will passed from
generation to generation to make sure that the
offspring belong to the same species having
similar characteristics.
Organisms grow and develop according to its
genes that gives instruction that will direct the
cellular growth and development ensure that
the offspring will grow up and manifest many of
the same characteristics from the parents.
Mitosis and meiosis play an important role in this
Living things take in minerals and food from the
environment to survive and grow. It is the
process of which organism obtain energy and
raw materials from nutrients such as fats,
carbohydrates, and proteins
It is the process in which the energy from the
food eaten is being released in all living cells.
Organisms break down the food within their cells
with a specific process to carry out the following

Lesson 2 | Evolving Concept of Life Based on Emerging Pieces of Evidence
All living things move. Animals move from one
place to another. Plants also move but not as
usually observable than animals. Plants move in
different ways in order to grow and their
movement may be so slow that people cannot
even recognize. A Makahiya leaf being
touched is an example of movement through
All living things also excrete but in different ways.
Excretion is the result of many chemical
reactions happening in cells which they must
remove the waste products which might poison
the cells. Excretion is the removal of toxic
minerals in excess from the organism.

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