The origin of life on Earth is a mystery of science, with no widely accepted theory but many hypotheses supported by evidence. The earliest known fossils are 3.5 billion years old, but there is evidence that bacteria-like organisms lived on Earth 3.5 billion years ago, and may have existed even earlier, when the first solid crust formed, almost 4 billion years ago. Scientists think that early life may have formed from lighting strikes or arisen in deep sea vents.

1. EMERGENCE OF THE FIRST
LIVING CELL
HARD CORE- 2.3
RASHMI M G
P01AG23S028017
MAHARANI’S SCIENCE COLLEGE FOR
WOMEN
MYSORE

2. INTRODUCTION
• Origin of life is one of the most fascinating
problem in biology.
• Belief- life originated on the earth sometimes in
the remote past from non living substances.
• Life was eventual outcome of long process of
chemical evolution which took place during the
early stages of the earth’s history.
• Modern concept/ naturalistic theory- suggests
that there was no trace of life on this planet
about 2 billion years ago.
• Earth's origin – about 4.5 billion years ago.

3. Enormous
heat
generated
Atmosphere
contained many
lighter elements in
gaseous state
It contained water,
ammonia,
methane,
hydrogen
sulphide,
hydrogen,
nitrogen, carbon
dioxide
Gradually
cooled.
Upper crust
became
hardy and
rocky
Below the
surface had
trapped
Hydrogen and
oxygen molecules
were condensed
into water
Water
escaped from
the Earth and
formed
atmospheric
vapour
Earth’s
surface
cooled
gradually,
condensing
of vapour
into water
poured down
into rain
Unending downpour resulted
in erosion of rocks on the
Earth forming vast ocean
Minerals commonly found
in oceans formed a
prebiotic soup

4. PREBIOTIC EARTH
• Generally it is believed that the primitive forms of life must have
depended on some kind of energy.
• Agents responsible for catalytic reactions in the prebiotic Earth are-
sunlight, ultraviolet radiations, electric discharges and heat.
• Electric discharges catalyze reactions to synthesize molecules, a
phenomenon that has been experimentally proved.
• Sunlight can produce large amount of oxygen by splitting water and
producing hydrogen, which is capable of enhancing the reducing
power of the atmosphere.
• Haldane long ago suggested that in the prebiological Earth
ultraviolet radiations were responsible for generation of complex
molecules. As evidenced by the presence of formaldehyde and
glyoxal in mixtures irradiated with UV rays

5. Urey' postulates
Earth cloud contained hydrogen, methane, inert gases,
iron compounds, ammonia silicates
It was originally a very hot and homogeneous gaseous ball
Cooled down due to cosmic cooling effect and 3 zones
became differentiated- core, mantle, solid crust
Condition of primitive earth were not suitable for life as
free oxygen was not available in the earth’s atmosphere.
Oxygen was in combined state either in the form of
water or as oxides .

6. Mantle (2900km)
Crust (8-40km)
Core(2500km)
Formation of core, mantle, crust of
earth

7. In the cooling process,
several physical
changes took place
as a result of these
changes oceans and
mountains were
formed
Chemical reactions
took place.
Water was first formed
was not in liquid state
but remained in
vaporized state for
long time.
Water vapour
accumulated and
became condensed to
form dense cloud
around the earth
Water vapour on
cooling precipitated in
the form of rain drops
Rain drops reaching the
hot surface and
vaporized and the
vapour again
accumulated to form
clouds
Water accumulated
formed oceans and
other water bodies
Volcanoes and fissures
gushed methane,
steam, ammonia and
carbon dioxide
accumulated around
the earth and formed
earth’s first
atmosphere
Air contained 4
elements of life-
carbon, hydrogen,
oxygen, nitrogen
Short wave cosmic
radiations or UV
radiations and was
stabbed by incessant
lightning
Origin of earth
and its atmosphere

8. How life originated on this earth?
1924, A I Oparin, put forth the concept that living matters
might have originated form the on-living or inorganic
matters.
Accepted by JBS Haldane and R Bentner
Oparin’s book ‘the origin of life’ in 1936, in which he
stated that in the first place carbon must have been
present in the atmosphere or primitive earth in the form
of hydrocarbon .
Hydrocarbons might have united with other compounds
to produce a variety of organic compounds –alcohols,
aldehydes, carboxylic acids.
Some of carboxylic acids reacted with ammonia to form
amino acids, the basic molecules of life.

9. Miller’s experiment
CH4
NH2
H2O
ELECTRIC DISCHARGE
GASEOUS MIXTURE
COOLING JACKET
TRAP
BOILING WATER FLASK
VACCUM PUMP
AMINO ACID

10. Miller’s experiment
1953, Stanley Miller, a student of Dr. Urey performed one
such experiment in which he exposed a mixture of water
vapour, methane, ammonia and hydrogen gases to
continuous electric sparking for a week and at the end of
the experiment he found sugars, aldehydes, amino acids
such as glycine, alanine and number of more complex
organic compounds.
This experiment provided clue that such complex organic
compounds were formed in the atmosphere as a whole in
the remote past during continuous rains and lightning.
Cosmic radiations might have made the course of reactions
more easy by supplying tremendous energy required in the
process

11. Pyrimidines nucleoproteins
Purines nucleotides
Amino acids proteins
Glycerol fats
Sugars polysaccharides
Formation of organic chemicals in
primitive ocean

12. Spherules (coacervates)
Coacervates
Dr. Calvin has estimated that molecular life must have evolved about 2 billion years before
the first living cell appeared.
Fox, Harada and Kendrick (1959) have reported that a large number of small uniform
microscopic elastic spherules with firm outline were formed when hot saturated solution of
proteinoides was cooled down.
These spherules behaved in many ways like bacteria and they clung together in chains as
one celled blue green algae sometimes do.
Although these spherules are not true cells, as they lack Deoxyribose nucleic acid (DNA)
and genes and they are simpler than any other contemporary life, yet they do possess
many cellular properties.

13. Origin of first living organisms

14. Anaerobic phase rich in
Hydrogen and with energy
entering the system as UV
rays, ionizing radiations,
potential chemical energy
and local heat which was
responsible for the initiation
and accumulation of organic
substances
Anaerobic phase
poor in Hydrogen
when slow
accumulation of
molecular oxygen
blocked the
penetration of short
wave UV rays.
the oxygen
assumed the
state of
excitation and
became ozone
Simple anaerobic
organisms
distinguishable from
their surroundings
such as purple
bacteria came into
existence
Depletion of accumulated
organic substances from the
environment by anaerobic
micro organisms of the early
period with anaerobic
photosynthesis utilizing
visible light as the energy
source.
Intense competition was set
Combination of Porphyrins
and manganese-protein
complexes led to the
formation of chlorophyll and
then the photosynthesis of
typical green plant cells
became dominant
Liberation and
accumulation of free
oxygen into
atmosphere and
water led to the
disappearance of
anaerobic organisms
Oxygen itself became an evolutionary force which caused
extinction of most anaerobic microbes and at the same
time enabled achlorophyllous descendents of green cells
as animal cells to make use of energy potential of
biological oxidation of organic substances

15. CONCLUSION
The origin of life is a gradual event occurred
several years ago in the primitive earth about
4.5 billion years ago. It is suggested that it is
formed by inorganic components with the
absence of oxygen in primitive earth. Several
experiments, postulates have proved this fact.

16. REFERENCE
Cell Biology, Genetics, Molecular Biology,
Evolution and Ecology: Evolution By PS
Verma, VK Agarwal.