How life originated on earth is still a very tough question. We have found many evidences, we have a lots of hypothesis, but still we have miles to go. This PPT summarizes the findings of research on origin of life on earth.

1. ORIGIN OF LIFE ON EARTH
JANMONI BORAH
BARNAGAR COLLEGE

2. DEFINITION OF LIFE
• There is not a single, perfect definition of life, because life is a
process, it is not a substance.
• One popular definition is that organisms are open systems that
maintain homeostasis, are composed of cells, have a life cycle,
undergo metabolism, can grow, adapt to their environment, respond
to stimuli, reproduce and evolve.
• According to NASA, life is “a self-sustaining chemical system capable
of Darwinian evolution:.
• More simply, life is “matter that can reproduce itself and evolve”

4. DIFFERENT TYPES OF LIFE

5. TYPES OF CELL : PROKARYOTIC AND
EUKARYOTIC

6. BIOMOLECULES
• Biomolecules are special molecules of Carbon.
• Carbohydrates, lipids, proteins and nucleic acids are the main
classes of biomolecules.
• Carbohydrates provide energy, lipids are the main structural
components of cell membranes, proteins are the building
blocks and catalyst.
• DNA and RNA are the peculiar class of biomolecule that can
reproduce and replicate themselves. They also act as the
genetic and hereditary material.

8. ORIGIN OF LIFE
• Almost every religion believe God created the earth and all the organisms.
• Charles Darwin was the first person to challenge the God as the creator and
he postulated that all the organisms on the earth evolved through natural
selection from a single common ancestor who existed long long ago.
• Some people believe the seed of life on earth came from other parts of the
universe along with meteorites and this theory is called the ‘panspermia’
theory.
• Till today, our Earth alone is known to host life. There may be billions of
earth like places in the universe with more advanced civilizations, or may
not be. Titan and Europa, two moons of Saturn are strongly believed to be
home of living forms in our solar system.

9. THE PREBIOTIC EARTH
• Our solar system originated about 4.567 billion years ago.
• During the first billion years, earth was inhospitable to life. It
was very hot, there was no water, soil, oxygen.
• The oldest fossil till discovered dated 3.8 billion years ago.
• It is now impossible to recreate the original environment of
earth in laboratory. It is unknown where and when exactly the
first life originated on earth.

10. THE ABIOGENESIS THEORY
• Oparin and Haldane(1929) postulated that life originated in the primitive
environment of earth from simple inorganic substances.
• Different lighter atoms like Hydrogen, oxygen, nitrogen, carbon etc.
combined to each other to form inorganic compounds like NH3, H2O, H2S
etc. The energy required for such chemical reaction was obtained from
sunlight, volcanic activity, thunderstorm etc.
• These simple inorganic molecules further reacted with each other to form
some simple organic molecules like amino acids, sugars, nucleotides etc.
• Small organic molecules polymerized to form large biomolecules like
carbohydrates, lipids, protein, nucleic acids etc. These molecules later
organized themselves to form the first cell-like structure which can
reproduce and evolve.

11. UREY AND MILLER’S EXPERIMENT
• Experimental proof to the abiogenesis theory was provided by Urey
and Miller(1951)
• They tried to recreate the primitive environment of earth in
laboratory. CH4, NH3, H2 and H20 was kept in a specially designed
chamber for almost a week, provided with heat and electric shock.
• They analysed the water after the completion of the experiment and
confirmed the presence of simple amino acids, sugars etc.
• This experiment proved that the biomolecules necessary for life
process were created from simple inorganic molecules in primitive
environment of earth.

13. • Almost all scientists now a days believe this theory of inorganic
origin of life.
• Darwin postulated hot primitive ponds to be origin of life.
• Some scientist believe under surface uranium-rich pockets served
as the home for primordial life.
• Underwater volcanos, hot springs etc are also believed to be the
first place where life first originated.

14. • Darwin’s warm little pond

15. UNDERWATER VOLCANIC POCKETS

16. LUCA (LAST UNIVERSAL COMMON
ANCESTOR)
• With the help of tools of molecular biology, the probable
ancestor of all life forms on present day earth has been traced,
and found to be an organism who lived almost 3.8 billion years
ago. But no fossil evidence found till date.
• It shares almost 350 genes with all life forms.
• It was an unicellular prokaryotic microbe.
• It was chemotrophic.
• It had RNA as genetic material.

17. LUCA

18. EVOLUTION
• Evolution is the process by which one life form gradually changes to
a different one. It is a very slow but continuous process.
• All the living organisms on earth are the result of evolution. All
organism, including human, continue to evolve.
• Evolution started from the point of formation of first organic material
on earth. Hence, organic evolution.
• Forces behind evolution include mutation, chromosomal
abberrations, natural selection, bottleneck effect, genetic drift etc.

19. • Origin of life

20. THANK YOU