THE NATURE AND
ORGIN OF LIFE
PRESENTED BY: Iqra Iftikhar (s/2019-2431)
Aneeza Shahid (s/2019-2433)
Presented to: Mam Dr. Zahra Hussain
Subject: Advanced Zoology IV
EVOLUTION
Nature and origin of life
The origin of life is a scientific problem which is not yet solved.
There are plenty of ideas, but few clear facts.
Verse
Did the unbelievers (who do not accept the teaching of the Prophet)
not realize that the heavens and the earth were one solid mass, then
We tore them apart, and We made every living being out of water?
(21:30)
Introduction
 It is presumed that the universe came into existence with a single
titanic explosion called big bang about 15000 million year ago.
 The fragments of the fire ball expanded and cooled to give rise to
many celestial bodies.
 This results in the formation of solar system consisting of sun and
planets.
 The Earth originated about 4.6 billion years ago.
 Earlier life was thought to be created by some super natural power.
 Origin of life on Earth is also called protobiogenesis.
 Several attempts have been made from time to time to explain the
origin of life on earth.
 As a result, there are several theories which offer their own
explanation on the possible mechanism of origin of life.
 Following are some of them:
Theory of Special Creation
Theory of Spontaneous Generation
Theory of Biogenesis
Theory of Catastrophism
Theory of Cosmozoic and panspermia
Modern Theory of Oparin / Haldane
 Theory of special creation –Mythology based theory
Supporter of this theory was father Suarez. According to Bible
life and everything was created by god in 6 days.
 1st day: Earth and heaven
2nd day : Sky and water
3rd day : Land and plants
4th day : Sun, moon and stars
5th day : Fishes and birds
6th day : Land animals and first man Adam and from his 12th Rib
first woman Eve.
 Theory of special creation was the theory that had only religious
belief and proved that organisms are created as they are. The
scientists were unable to prove it scientifically. Theories that came
in contradiction to the theory of special creation were the theory of
spontaneous generation.
 According to hindu mythology the world was created by God
Brahma. (The first man was Manu and the first woman was
Shraddha). According to it life has not changed ever since its
origin. Special creation theory lacks scientific evidences so it is not
accepted.
Theory of Spontaneous Generation
 A popular theory that was held throughout the middle ages until the 19th century, is the
hypothesis that some vital force contained in or given to organic matter can create living
organisms from inanimate objects.
 A theory that complex life was thought to arise spontaneously and continually from
nonliving matter.
 This theory is NOT true but it was believed for almost 2000 years • People observed
things that made them think living things could come from non-living things
 This theory was disproven by the experiments that used the scientific method as early as
the 17th century and decisively rejected in the 19th century
 The idea that life came from nonlife more than 3.5 billion years ago on Earth. .
 Aristotle (384-322 B.C. )
 He proposed that worms, insects, fish, frogs and even mice Developed from soil.
 Tapeworms from the excreta of animals, crabs salamanders from the earth and slime.
Theory of biogenesis :
 Biogenesis is the formation (production) of new living organisms or
organelles. Theory of biogenesis states That , life does not
spontaneously arise from non-living material.
 This theory could not explain first life on earth but able to explain
continuity of life.
 Living organisms are always produced from pre-existing living
forms by reproduction and not from non-living or lifeless matter.
 According to Louis Pasteur living things come only from other
living things, by means of reproduction.
Francesco Redi (1668)
 In 1668, Francesco Redi, an Italian physician, did an experiment with flies and
wide-mouth jars containing meat.
 He took rotting meat pieces in jars. He sealed some of these jars tightly and other
left open.
 After few days maggots appeared in open jars in which the flies went freely in
and out and laid their eggs on meat.
 But in sealed jars in which the flies could not enter did not show any maggots.
 Redi concluded that the maggots arise from the eggs laid down by the parent flies
and that the maggots can not appear spontaneously.
 Redi set up new experiment in which he covered jars with fine muslin cloth of
sealing them tightly and allow free air in out of the jars.
 After some time maggots appeared only in some jars.
 Redi concluded that free air considered as vital force necessary for spontaneous
origin.
Francesco Redi experiment
Lazzaro Spallanzani’s Experiment:
 Italian scientist Spallanzani poured hay infusion in eight bottles and boiled
all of them.
 He four eight bottles just corked other four were made airtight.
 He observed a thick layer of microorganisms in the corked bottles.
 To the porous nature of the cork, outside air was in contact with the
matter inside the corked bottles. There was no formation of
microorganisms in airtight bottles.
 He concluded that air contains microorganism which came in
contact with the matter in the corked bottles and is the cause of
contamination and formation of microorganisms.
Theory of Catastrophism of Origin of Life:
 This theory was given by Georges Cuvier.
 It is a modification of the theory of special creation.
 According to this theory, there have been several creations of life by
God, each preceded by a catastrophic event due to some kind of
geological disturbance. Each catastrophe completely destroyed the
existing life and new life is created by God again.
 Each new creation consisted of life forms different from that of
previous ones.
 This theory has no practical evidence.
Cosmozoic Theory
 This idea was proposed by Richter in 1865 and supported by
Arrhenius (1908).
 According to this theory, life has reached the planet Earth from other
heavenly bodies such as meteorites, in the form of highly resistant
spores of some microorganisms. The spores of some
microorganisms are called cosmozoa or panspermia because they
are preserved inside meteorites coming to the earth from the outer
space.
 These meteorites struck the barren earth to release the cosmozoa and
they developed into different creatures on the earth.
 This theory lacks evidence.
Cosmic panspermia theory:
 Proposed by Arrhenius.
 According to this theory organisms existed throughout the universe
and their spores could freely travel through space from one star to
the other.
Modern Theory or Oparin-Haldane
Theory of Origin of Life:
 Oparin-Haldane theory is also called chemical theory or
naturalistic theory. A. I. Oparin (1894-1980) was a Russian Scientist.
He published his book “The origin of Life” in 1936.
 According to this theory ‘life’ originated upon our earth spontaneously
from non-living matter.
 This is called chemical evolution which cannot occur under present
environmental conditions upon earth. Conditions suitable for origin of life
existed only upon primitive earth.
 Atoms 》Molecules 》Simple Compounds 》Complex Compound 》
Living Cell
Modern Theory or Oparin-Haldane
Theory of Origin of Life:
 Chemical Evolution
 Biological Evolution
Chemical Evolution:
 . The atomic stage:
The earth was originated about 4.6 billion years ago. Early earth had
free atoms of all those elements which are essential for the
formation of protoplasm. The lightest atoms like carbon, hydrogen,
nitrogen and oxygen formed the primitive atmosphere. Most
abundant of all of them was hydrogen.
Formation of Inorganic Molecules:
 Free atoms combined to form inorganic molecules such as
H2 (Hydrogen), N2 (Nitrogen), H20 (Water vapour), CH4 (Methane),
NH3 (Ammonia), C02 (Carbon dioxide). Hydrogen atoms were most
numerous and most reactive in primitive atmosphere.
 First hydrogen atoms combined with all oxygen atoms to form water
and leaving no free oxygen. Thus primitive atmosphere was reducing
atmosphere (without free oxygen) unlike the present oxidising
atmosphere (with free oxygen).
 Hydrogen atoms also combined with nitrogen, forming ammonia
(NH3). So water and ammonia were probably the first molecules of
primitive earth.
Formation of Simple Organic Molecules
(Monomers):
 The early inorganic molecules interacted and produced simple organic
molecules such as simple sugars (e.g., ribose, deoxyribose, glucose, etc.),
nitrogenous bases (e.g., purines, pyrimidines), amino acids, glycerol, fatty
acids, etc.
 Torrential rains must have fallen. As the water rushed down, it must have
dissolved away and carried with it salts and minerals, and ultimately
accumulated in the form of oceans. Thus ancient oceanic water contained
large amounts of dissolved NH3, CH4, HCN, nitrides, carbides, various gases
and elements.
 CH4 + C02 + H20 —> Sugars + Glycerol + Fatty Acids
 CH4 + HCN + NH3 + H20 —> Purines + Pyrimidines
 CH4 + NH3 + C02 + H20 —> Amino Acids
Chemical Evolution
 Some external sources must have been acting on the mixture for
reactions.
 These external sources might be:
(i) solar radiations such as ultra-violet light, X-rays, etc.
(ii) energy from electrical discharges like lightning
(iii) high energy radiations
 There was no ozone layer in the atmosphere.
 A soup-like broth of chemicals formed in oceans of the early earth
from which living cells are believed to have appeared, was termed
by J.B. Haldane (1920) as ‘prebiotic soup’ (also called ‘hot dilute
soup’).
 Organic compounds accumulated in water because their
degradation was extremely slow in the absence of any life or
enzyme catalysts.
Formation of Complex Organic Molecules
(Macromolecules):
 The small simple organic molecules combined to form large
complex organic molecules.
 For Example:
 Amino acid units joined to form polypeptides and proteins, simple
sugar units combined to form polysaccharides, fatty acids and
glycerol united to form fats, sugars, nitrogenous bases, and
phosphates combined into nucleotides which polymerized into
nucleic acids in the ancient oceans.
 Sugar + Sugar ———-> Polysaccharides
 Fatty Acides + Glycerol ———-> Fats
 Aminoacids- + Aminoacids ———–> Proteins
 Nitrogenous Bases + Pentose Sugars + Phosphates ———>
Nucleotides
 Nucleotides + Nucleotides ———–> Nucleic Acids
Experimental Evidence:
 By Stanley Miller. Who was a student of Harold Urey. In this experiment Miller took
the mixture of methane, ammonia and hydrogen (ratio 2 : 1 : 2) in a large flask and
passed steam over it by boiling water and connecting it with a glass tube. Electric
spark was discharged at 800 °C in the mixture by using two tungston electrodes as
source of energy.
After 18 days this fluid was collected and analysed. This dark red fluid was found
to contain.
 Simple amino acids – glycine, alanine, aspartic acid.
 Simple organic acids – farmic, acetic, oxalic, lactic, succinic acids. etc.
Biological Evolution:
 On Earth life began at least 4 billion years ago and it has been evolving
every year.
 In the beginning all living things on earth were single celled organism,
after several years multicellular organism evolved after that diversity in life
on earth increased day by day.
1. Protobionts or Protocells:
 An aggregation of organic molecules, surrounded by a membrane, that
abiotically coalesces into resemblances of living matter; thought to be the
precursors of prokaryotic cells.
 These are at least two types of fairly simple laboratory produced
structures— Oparin’s coacervates and Fox’s microspheres which possess
some of the basic essential of proto cells.
(i) Coacervates:
 The first hypothesis was proposed by Oparin (1920). According to this
hypothesis early proto cell could have been a coacervate. Oparin gave
the term coacervates. These were non-living structures that led to the
formation of the first living cells from which the more complex cells have
today evolved.
 Oparin speculated that a proto cell consisted a carbohydrates, proteins, lipids and nucleic
acids that accumulated to form a coacervate. Such a structure could have consisted of a
collection of organic macromolecules surrounded by a film of water molecules.
 This arrangement of water molecules, although not a membrane, could have functioned
as a physical barrier between the organic molecules and their surroundings. They could
selectively take in materials from their surroundings and incorporate them into their
structure.
 Coacervates have been synthesized in the laboratory. They can selectively absorb
chemicals from the surrounding water and incorporate them into their structure. Some
coacervates contain enzymes that direct a specific type of chemical reaction.
 Because they lack a definite membrane, no one claims coacervates are alive, but they do
exhibit some life like characters. They have a simple but persistent organization. They
can remain in solution for extended periods. They have the ability to increase in size.
(ii) Microspheres:
 A microsphere is a non-living collection of organic macromolecules
with double layered outer boundary.
 The term microsphere was given by Sydney Fox.
 Sidney Fox demonstrated the ability to build microspheres from proteinoids.
 Proteinoids are protein like structures consisting of branched chains of amino acids.
Proteinoids are formed by the dehydration synthesis of amino acids at a temperature of
180°C.
 Some of the proteinoid material produces a double-boundary structure
that encloses the microsphere.
 They do exhibit some membrane like characteristics and suggest the
structure of a cellular membrane.
 They have the ability of motility, growth, binary fission into
two particles and a capacity of reproduction by budding and
fragmentation.
 Their budding resembles with bacteria and fungi.
Origin of Prokaryotes:
 Prokaryotes were originated from proto cells about 3.5 billion years ago in the sea.
 The atmosphere was anaerobic because free oxygen was absent in the
atmosphere.
 Prokaryotes do not have nuclear membrane,cytoskeleton or complex organelles.
 They divide by binary fission.
Evidence of Ancient Life
 Stromatolites:
 Stromatolites are the oldest known
macrofossils
 3.2 billion years ago
 Layers of sediment left by
cyanobacterial mats
Oxygen Revolution:
 As the number of photoautotrophs increased, oxygen was released
in the sea and atmosphere. Free oxygen than reacted with methane
and ammonia present in the primitive atmosphere and transformed
methane and ammonia into carbon dioxide and free nitrogen.
 CH4 + 202 ————- > CO2 + 2H2O
 4NH3 + 3O2 ———– > 2N2 + 6H2O
Formation of Ozone Layer:
 As oxygen accumulated in the atmosphere, the ultraviolet light changed some of oxygen
into ozone.
 2O2 + O2 ———- > 2O3
 The ozone formed a layer in the atmosphere, blocking the ultraviolet light and leaving the
visible light as the main source of energy.
Origin of Eukaryotes:
 About 1.5 billion years ago.
 The first eukaryotes evolved from ancestral prokaryotes by a process
endosymbiosis that involved internalization of prokaryotes by an ancestral
eukaryotic cell, resulting in the formation of the mitochondria and
chloroplasts.