Earth and Life Science
Quarter 2
MODULE
1
Week 1
Introduction to Life Science
Historical Development of the Concept of Life
We are part and we live in a vast universe that we have only begun to explore. Up to now, we know
of only one planet – Earth – that has life and has liquid water. In addition, the similarities of biochemical,
metabolic, and genetic make-up among Earth’s species imply that all evolved from a common ancestor that
lived billion years ago.
This module will focus on historical development of the concept of life. It will provide you with
information and activities that will help you understand and appreciate the essence of life.
After going through this module, you are expected to:
1. explain the evolving concept of life based on emerging pieces of evidence (S11/12ES-IIa-1).
Activity 1: Picture Analysis
On this specific activity your honesty is a must. This is just a self- assessment if you have previous knowledge
on the topic we’re going to discuss. You may write your answer in your activity notebook. Just try it. Answer
key is provided on the last page of this module.
Observe the picture above. It shows a timeline of the history of life on Earth. Give three (3) observations
about the picture.
1. ______________________________________________________________________________
2. ______________________________________________________________________________
3. ______________________________________________________________________________
Think about the first life forms on Earth. Many theories about the origin of life have emerged. Cite at least
one theory that you know and explain it briefly.
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
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The Earth began to exist about 4.6 billion years ago. As believed by many scientists, the existence of life
started from the moment the Earth’s environment became stable to support life. For billions of years now, life is believed
to have existed on Earth. Scientists do not precisely know when did life begin on planet Earth.
However, they can trace how life has developed and evolved using some pieces of evidence.
Origin of Life
There are many emerging theories about the origin of life. Some believed that living organisms
were placed and put to Earth by some divine forces. Others say that life originated from other planets, not from
Earth. But among scientists and theorists, the most accepted theory about the concept of life is that life came
from inanimate matter.
Primordial Soup Theory
This theory was proposed by Alexander Oparin and John Haldane. According to this theory, life
started in a primordial soup of organic molecules. Some form of energy from lightning combined with the
chemicals in the atmosphere to make amino acids, the building blocks of protein.
Also, several scientists conducted different experiments that modeled conditions which may have
enabled the first life forms to evolve. Among these experiments are: the Electrical Discharge Experiment,
Thermal Synthesis, and The Protocell Experiment.
Electrical Discharge Experiment
In this experiment, Stanley Miller and Harold Urey verified the primordial soup theory by simulating the
formation of organic molecules on the early Earth. They had confined methane, ammonia, water, and hydrogen
in a closed system and applied continuous electrical sparks to trigger the formation of the building blocks of
life. They observed a change of color in the solution after a day. After a week, the solution was tested. They
found out that several amino acids were produced. The purpose of this experiment was not to try and produce
amino acids. Its main purpose was to explore and discover the conditions of the early Earth and what the
naturally occurring results would be.
Thermal Synthesis
Sidney Fox demonstrated in his experiment the origin of life with the use of a specific mixture of
pure, dry amino acids. As observed in his experiment, after heating the mixture, an aqueous solution was formed
and cooled into microscopic globules called protenoid microspheres. The globules looked like coccoid bacteria
and seemed to be budding. Budding is a form of reproduction in some microorganisms. Sidney Fox claimed
that the protenoid microspheres constituted protocells – almost true cells and multiplied through division like
true cells. He believed that these cells were the link between the true living cells and the primordial
environment.
The Protocell Experiment
In this experiment, Jack Szostak contemplated on how early life forms formed in a primordial
chemical environment. Szostak then thought that the simplest possible living cells or protocells just required
two components to be formed. The components include: a nucleic acid genome to transmit the genetic
information and a lipid sac which encapsulated the genome and let itself grow and divide.
Szostak developed and built lipid sacs made in fatty acids and a replicase – an RNA molecule that
catalyzes its own replication in the test tube. He discovered that lipid sacs with more RNA grew faster. He
recommended that such test tube evolution was possible. The results suggested that the early life forms with
just a single gene, an RNA gene, could have undergone a Darwinian evolution.
Early Forms of Life
About 3.5 billion years ago, the first form of life is believed to have appeared. The first evidence
of life is found and seen in microfossils – are fossils that contain the remains of tiny plants and animals. These
are very small and can be measured in millimeters. Some could only be identified under a microscope.
Some of the remains of organisms do not have a nucleus so they were called as prokaryotes – they
are known to be the earliest forms of life. They have endured and survived the extreme conditions of the early
environment. They started to produce and make their own food by utilizing the carbon dioxide in the atmosphere
and the energy from the sun. These are the photosynthetic organisms. The process of photosynthesis produced
more oxygen that modified and changed the Earth’s early atmosphere. This change in the atmosphere has
allowed oxygen-breathing organisms to exist. The first photosynthetic organisms to form are the cyanobacteria.
Their microfossils are among the easiest to identify. Their morphology remained the same, and they left
chemical fossils in the form of broken products from pigments.
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The first microfossil was seen in rocks about 1.5 billion years old. It showed remains of organisms
with differences in structure from the simple form of life. They are larger than bacteria, and they have internal
membranes and thicker wall. These findings have marked the beginning of eukaryotic organisms on Earth.
How did multicellular organisms evolve?
It is believed that multicellular organisms have evolved from unicellular eukaryotes. Some single
eukaryotic cells, like unicellular algae, formed multicellular aggregates through association with another cell
producing colonies. The organisms evolved to form multicellular organisms from colonial aggregates through
cell specialization. Protozoans, sponges, and fungi came to being.
The first fossilized animals which were found 580 million years ago were soft- bodied. The
emergence of complex and diverse plants and animals, including human beings was brought about by the
continuous process of cell specialization.
Evidence from fossil layers had proved that different forms of life were present and have evolved
through time. According to Charles Darwin, organisms change over time because of adaptation to their
environment to survive. He published his thoughts about evolution and natural selection in his book – On the
Origin of Species.
Activity 2: Match Me! Choose the letter of the best answer. On this specific activity your honesty is a must.
This is just a self- assessment if you learned something on the topic we discuss. You may write your answer in
your activity notebook. Just try it. Answer key is provided on the last page of this module.
A. Electrical Discharge Experiment
B. Primordial Soup Theory
C. Thermal Synthesis
D. The Protocell Experiment
_____ 1. Simulated the formation of organic molecules on the early Earth
_____ 2. The combination of chemicals in the atmosphere and energy from lightning had formed amino acids.
_____ 3. Performed by Jack Szostak
_____ 4. Used a mixture of dry amino acids
_____ 5. Proposed by Oparin and Haldane
_____ 6. The proponent of this experiment is Sidney Fox
_____ 7. Used a nucleic acid genome to transmit the genetic information and a lipid sac to let itself grow and
divide
_____ 8. Miller and Urey demonstrated this experiment
Important Reminder:
If you have queries, please do not hesitate to contact me.
Ma’am Carren G. Parungao - 0975-928-5229
Subject Teacher
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