Life, living matter are those that shows certain attributes that include responsiveness, growth, metabolism, energy transformation and reproduction. In biology origin of life or abiogenesis is the natural process by which life has arisen from non-living matter, such as simple organic compounds. It means the emergence of heritable and evolvable self-reproduction. It is a complex subject and oftentimes controversial. Several attempts have been made from time to time to explain the origin of life on earth. There are several theories which offer their own explanation on the possible mechanism of origin of life.

1. ASSAM UNIVERSITY, SILCHAR
DEPARTMENT OF LIFE SCIENCE
PRESENTED BY:
KUKI MONJORI BORUAH
ROLL NO- 11
DEPT. OF EARTH SCIENCE
ORIGIN OF LIFE

2. CONTENT
INTRODUCTION
EVIDENCE FOR ORIGIN OF LIFE
THEORIES OF ORIGIN OF LIFE
 PRE-MODERN THEORIES
 MODERN THEORIES
RECENT DEVELOPMENTS
CONCLUSION
REFERENCES

3. INTRODUCTION
 Life, living matter are those that shows
certain attributes that include
responsiveness, growth, metabolism,
energy transformation and reproduction.
 In biology origin of life or abiogenesis is
the natural process by which life has
arisen from non-living matter, such as
simple organic compounds.
 It means the emergence of heritable and
evolvable self-reproduction.
 It is a complex subject and oftentimes
controversial.

4. EVIDENCE FOR THE ORIGIN OF LIFE
 There are at present four primary sources of information
a) The record of the early solar system, as preserved in
comets or carbonaceous chondrites.
b) The record of terrestrial rocks- geology.
c) The record of ancient microorganisms and their
physiological activities- palaeobiology.
d) The phylogenic history recovered in the nucleotide
and amino acid sequences found in molecular cells-
molecular phylogeny.

5. THEORIES OF ORIGIN OF LIFE
 Several attempts have been made from time to time to
explain the origin of life on earth.
 There are several theories which offer their own
explanation on the possible mechanism of origin of life.
 They can be categorized into two groups-
 Pre-Modern theories
 Modern theories

6. ORIGIN
OF LIFE
SPECIAL
CREATION
EXTRA-
TERRESTRIAL
ORIGIN
SPONTANEOUS
ORIGIN
BIOCHEMICAL
EVOLUTION
SINGLE
BEGINING
RNA
WORLD
CHILLY
START
DEEP SEA
VENT
COMMUNITY
CLAY
ELECTRIC
SPARK

7. PRE-MODERN THEORIES
 THEORY OF SPECIAL CREATION
o Life formation on the earth have
been taken place due to
supernatural or divine forces.
o It has no scientific explanations.
o Hindu Concept- lord Brahma
created the living world in one
stroke.
o Christian and Islam Concept-
God created this universe, plants,
animals and human beings in
about six days.

8.  THEORY OF SPONTANEOUS
ORIGIN
o Life may have evolved from
non-living things, decaying and
rotting matter like straw, mud
etc.
o Hypothesis was generated by
Aristotle.
o According to Aristotle, every
living being is made up of a
compound of matter and form.
o He believed that male semen and
female matter (menstrual blood)
were produced by bodies as a
result of their proportions of
heat, ingested food and were a
byproduct of the elements earth
and water.

9.  THEORY OF BIOGENESIS
o Life comes from pre-existing life,
“Omnis vivum exovos”.
o In 1665, Redi’s Spallanzani and
Pasteur’s experiment proved that
all living things arise from other
living things and are composed of
minute cells.
o Italian scientist Francesco Redi,
is the first to disprove
spontaneous generation by
conducting an experiment.
o He placed thoroughly cooked
meat in three jars.
• one uncovered – maggots
developed
• Covered with parchment – no
maggots developed
• Covered with muslin – fly laid
eggs over it.

10. o John needham creates a rebuttal
towards Redi’s results and followed
by Spallanzani.
o Finally Louis Pasteur conducted an
experiment.
o Pasteur sterilized two swan neck
flasks and filled them with nutrients
containing broth which will allow
organisms to grow on it.
o The swan neck ensured that broth
won’t be contaminated by outside
air.
o No organism arose from the broth
showing that living organisms
cannot arise spontaneously.
o But when he broke one of the swan
necks living organisms appeared in
that one thus proving that organisms
can come from pre-existing

11.  THEORY OF EXTRATERRESTRIAL ORIGIN
o Given by Richter in 1865, and also known as theory
of Panspermia.
o Primitive life had come to the earth as seed or spores
from other heavenly bodies through meteorites.

12. MODERN THEORIES
 THEORY OF BIOCHEMICAL
EVOLUTION
o Presented in the 1923
independently by A.I. Oparin
and later supported by J.B.S.
Haldane in 1928.
o Life could have arisen through a
long series of physico-chemical
changes, first inorganic and then
organic compounds in
accordance with ever changing
environmental conditions.
o It can be studied in three
categories-
 Chemical evolution of life
 Biological evolution of life
 Cognogeny

13. Chemical Evolution of life
1.Formation of simple inorganic molecules
•The atmosphere of primitive earth had various elements like
hydrogen, oxygen, nitrogen etc. These free atoms combine
to form molecules and simple inorganic compounds like
ammonia, water vapour, HCN etc.
2.Formation of simple organic molecules
•The simple inorganic compounds formed in atmosphere
interacted and combined to produced simple organic
compounds such as simple sugars, purines, pyrimidines,
amino acids etc.
•The source of energy – UV rays, lightening, radiations from
radioactive rocks and heat of earth.
•Water bodies changed into a broth or premordial soup or
prebiotic soup.
•Stanley Miller and Harold Urey tested this step by used an
experimental set up to recreate what environmental
conditions were believed to be like on early earth known as
Urey Miller Experiment.

14. UREY MILLER EXPERIMENT
 Recreate what environmental
conditions were believed to be like
on early earth.
 Subjected methane, ammonia and
hydrogen (in 2:1:1 ratio) and steam
(coming from water boiling in small
flask) to electric discharge(sparking)
from electrodes in a large chamber
for about a week.
 Various types of amino acids,
purines and pyrimidines have
generated in the U-tube at the base of
the apparatus.
 Drawbacks
• By examining rocks dated to be 3.7
billion years old geologists
determined that earth had an
oxygenic atmosphere not rich in
methane and ammonia.
• Oxygen is an oxidizing agent and
would inhibit chemical evolution.

15. 3. Formation of complex organic molecules
•Simple organic compounds combined and
recombined through the process of condensation,
polymerization and oxido-reduction to form complex
organic molecules like proteins, polysacchrides,
peptides, polypeptides etc. in the primitive ocean.
•Synthesis of protein was the starting point for the
origin of life.
4. Formation of complex biomolecules
• In due course of time nucleotides underwent
polymerization to form nucleic acids- DNA and RNA
in primitive ocean.
• Enzymes and coenzymes came into existence.
• Certain enzymatic proteins associate with nucleic
acids forming nucleoproteins as self duplicating
system.

16.  Biological evolution of life
1. Formation of coacervates
The complex organic molecules of premordial soup in ocean
aggregated together through the colloidal system and
bounded water layer were called coacervates which were
presumed to formed in primitive water about 308 billion
years ago.
They are the intermediate between molecule and organism.
2. Formation of protocells
Some of the coacervates having DNA and RNA evolved
further and they developed lipoprotein membrane and
enzyme mediated reactions.
3. Formation of first cell
Protocells evolved into first true cell, the procaryotic
unicell.
They absorb organic molecules from outside for body
building and energy.

17. 4. Development of autotrophs
 When supply of existing organic
compounds was exhausted some of the
early procaryotes might have evolved into
autotrophs.
 They are capable of synthesizing their
own organic compounds by
chemosynthesis, hence chemoautotrophs.
 They develop the chlorophyll through
which the autotrophs can prepare the food
and oxygen evolved during this process
which are started to accumulate in the
atmosphere.
 Cognogeny
 With increased meant in number of
photoautotrophs oxygen released in great
extent in ocean and came into
atmosphere, thus an oxidising type
atmosphere has been formed.
 Procaryotes gradually modified to be
adapted to the aerobic mode of
respiration.
 Gradually many types of algae, fungi,
protozoa and other organic living
organisms developed.

18. DIAGRAMMATIC REPRESENTATION OF
BIOCHEMICAL EVOLUTION OF LIFE

19.  DEEP SEA HYDROTHERMAL
VENT THORY
• The deep-sea vent theory
suggests that life may have
begun at submarine
hydrothermal vents, spewing
key hydrogen rich molecules.
• These rocky nooks may have
concentrated molecules together
and provided mineral catalysts
for critical reactions.
• Today these vents, rich in
chemical and thermal energy,
sustain vibrant and strange non
photosynthetic ecosystem.

20. RECENT DEVELOPMENT
 In April 2011, researchers in Italy found that if they mixed
formamide, a simple chemical present in space, with material
from a meteorite, and then heated the mixture, that they
produced nucleic acids (building blocks of DNA and RNA),
the amino acid glycine and a precursor to sugar.
 In February 2010 scientists at the Scripps Research Institute
in San Diego announced that they synthesized RNA enzymes,
known as ribozymes, that can replicate themselves without
the help of any proteins or other cellular components.
 In May 2009, a team led by John Sutherland, a chemist at the
University of Manchester in England discovered how the
basic nucleotides of RNA could spontaneously assemble. He
formed the RNA nucleotide

21. CONCLUSION
All the evidence gathered thus far has revealed a
great deal about the origin of life, but there is still
much to learn.
Because of the enormous length of time and the
tremendous change that has occurred since then,
much of the evidence relevant to origin has been
lost.
Most relevant theory regarding the origin of life is
‘Theory of Biochemical Evolution’ by Oparin and
Haldane, because it is scientifically proven.
But none of these theories is 100% correct.
Research is going on to unravel the mystery of
origin of life.

22. REFERENCES
 Jain, P.C. and Anantharaman, M.S.: Palaeontology
(palaeobiology) evolution and Animal Distribution.
 Arora, P. Mohan; 3rd Edition: Evolutionary Biology.
 https://www.thedailystar.net/science/7-theories-the-
origin-life-77163
 https://bioprinciples.biosci.gatech.edu/module-1-
evolution/origin-of-life/
 https://www.lkouniv.ac.in/site/writereaddata/siteConten
t/202004261258144367alka_maths_Theories_of_life.p
df

23. THANK YOU