theories of origin of life

1. Origin of Life
Course: B.Tech Biotech
Subject: Basic of Life Science
Unit: I

2. ORIGIN OF EARTH
 The earth is presumed to have originated either
planetesimal hypothesis and nebular hypothesis.

3. Origin of the Universe
The universe began about 14.4
billion years ago
The Big Bang Theory states
that, in the beginning, the
universe was all in one place
All of its matter and energy
were squished into an infinitely
small point, a singularity
Then it exploded
The tremendous amount of
material blown out by the
explosion eventually formed the
stars and galaxies
After about 10 billion years, our
solar system began to form.
1.

4. Gradual condensation of interstellar dust from
which our entire solar system is presumed to be
formed.
The Nebular Hypothesis
2.

5. Earth is ~ 4,570,000,000 years old
The Age of the Earth
Meteorites give us access to debris left over from the
formation of the solar system
We can date meteorites using radioactive isotopes and their
decay products

6. THEORIES OF ORIGIN OF LIFE
 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:

7. 1. THEORY OF SPECIAL CREATION
 All the different forms of life that occur today on
planet earth : created by super natural power.
 This idea is found in the ancient scriptures of
almost every religion.
 Hindu mythology : Lord Brahma, the God of
Creation,
 Christian : God created this universe, plants,
animals and human beings in about six natural
days.
 Sikh mythology : all forms of life including
human beings came into being with a single word
of God.

8.  Special creation theory believes that the things
have not undergone any significant change since
their creation.
 The theory of Special Creation was purely a
religious concept, acceptable only on the basis of
faith.
 It has no scientific basis.

9. 2. COSMOZOIC THEORY (THEORY OF
PANSPERMIA
 According to this theory, life has reached this
planet Earth from other heavenly bodies(plnet or
stars) such as meteorites, in the form of highly
resistance spores of some organisms.
 Highly resistant spores : lead to life on earth,
named as “cosmozoa”.
 This idea was proposed by Richter in 1865 and
supported by Arrhenius (1908) and other
contemporary scientists.
 This theory lacks evidence, hence it was
discarded.

10. 3. THEORY OF CATASTROPHISM
 modification of the theory of Special Creation.
 It states that there have been several creations of
life by God, each preceded by a catastrophe
resulting from some kind of geological
disturbance.
 According to this theory, since each catastrophe
completely destroyed the existing life, each new
creation consisted of life form different from that
of previous ones.

11. 4. THEORY OF SPONTANEOUS
GENERATION/ABIOGENESIS
 Living organisms could arise suddenly and
spontaneously from any kind of non-living
matter.
 One of the firm believers in spontaneous
generation was Aristotle, the Greek philosopher.
 Dead leaves falling from a tree into a pond would
transform into fishes and those falling on soil
would transform into worms and insects.

12.  Some insects develop from morning dew and
rotting manure.
 Egyptians believed that mud of the Nile river
could spontaneously give rise to many forms of
life.
 Thales (624-548 BC) suggested that oceanic
water was the mother from which all living
forms originated.
 According to Empedocles life originated by itself
from non living matter and imperfect forms were
replaced by perfect forms.

13.  Aristotle (384-322 BC) proposed that living
forms are animated forms of non-living matter.
He further stated that the vital forces operate
constantly and improve the living world.
 In the 17th century the idea of abiogenesis was
opposed by an Italian physician Francisco Redi
(1621-1697). For the first time he proposed
through experiments, that life could arise only
from pre-existing living things.

14.  Experiment: sealing meat inside four closed
flask, while leaving another four meat filled
flasks open. Soon the meat in the open flasks was
full of maggots.
 Flies were entering and leaving the flask. Even
after many days no worm appeared in the closed
and sealed flask. This experiment confirmed his
idea that new life can come only from early life.

15. 14.2 The Origin of Life
Origins: Early Ideas
The History of Life
 Spontaneous generation is the idea that life arises
from nonlife.
 Francesco Redi, an Italian scientist, tested the idea
that flies arose spontaneously from rotting meat.
Chapter
14
3.

16.  The theory of biogenesis states that only living
organisms can produce other living organisms.
The History of Life
 Louis Pasteur designed an experiment to show that
biogenesis was true even for Microorganisms.
5. Theory of Biogenesis
Chapter
14
4.

17. Origins: Modern Ideas
Biochemical origin of life
 Simple organic molecule formation
 The primordial soup hypothesis was an
early hypothesis about the origin of life.
 Organic molecules could have been
synthesized from simple reactions.
 UV light from the Sun and electric
discharge in lightning might have been
the primary energy sources.
Modern Hypothesis of origin of Life
Chapter
14

18.  Stanley Miller and
Harold Urey were the
first to show that
simple organic
molecules could be
made from inorganic
compounds.
The History of Life
 Later, scientists found
that hydrogen cyanide
could be formed from
even simpler molecules
in simulated early Earth
environments.
14.2 The Origin of Life
Chapter
14
5.

19. THE ORIGIN OF LIFE
 Origin of life is NOT an event
 Origin of life is a continuous process
 Stages
inorganic production of key simple organic molecules
production of more complex molecules that can synthesize
more of the same molecule
development of a genetic code of self-replicating
molecules (RNA,DNA,proteins)
production of the first cell by separation of these codes
from the outer world by a membrane
 Ocean environment by 4.0 by- fossils evident at
3.8by

20. THE ORIGIN OF LIFE
 Many complex organic molecules must have formed
before an organism produced
 This process cannot occur on Earth today because the
simple organism would be destroyed by oxidation or
predation.

21. STEPS IN THE ORIGIN OF LIFE
 Aerobic vs. Anaerobic
 oxygen poisons living cells so early life was anaerobic
 Lack of free Oxygen >> No Ozone layer
 UV radiation kills cells so life had to originate at depth
 Water depths of 10m or more
 Models
 non-oxidizing secondary atmosphere rich in the constituent
chemicals for life--H2O, CO2, N
 Energy in the form of UV radiation & Hot springs

22. STEPS IN ORIGIN OF LIFE
 Before the first cell>>Chemical Evolution
production of significant molecules necessary for life
 Phosphoric acid -can bond molecules and promote
long chain molecule formation
 Amino acids formed first since they do not form if
oxygen present
probably formed on clay surfaces since they are attractive
and absorptive, also protection from UV
 Larger Molecules
amino acids are linked together by dehydration synthesis
(water loss), clays have potential to absorb water, thus
amino acids could be linked on clay surfaces

23. EXPERIMENTAL STUDIES A. I. Oparin- 1930s
Produced sugars and fatty acids from the constituents of
an early atmosphere
 Urey and Miller- 1953
Production of cyanide, formaldehyde and 4 different
amino acids from water vapor, methane, hydrogen and
ammonia and electrical sparks
 Subsequent Experiments
Production of 18 of the 20 known amino acids and
extremely simple forms of DNA from gases rich in water
vapor, CO2, and nitrogen and UV radiation
S.W. Fox (1959) produced protein-like (protenoids)
chains from a mixture of 18 amino acids at 70o
C in the
presence of phosphoric acid

24. THE ENVIRONMENT FOR LIFE
 Volcanic Hot Springs
 Oceanic hydrothermal
vent system
 Deep (below the level of
UV penetration)
 Clays and/or Zeolites as
templates
 Similarity with present
day chemosynthetic
heterotrophic organisms

25. THE FIRST CELLS
 All cells use the same genetic code
 Archaeobacteria- most primitive
Heterotrophs: obtain energy from surroundings by
some chemical reaction
Obtain energy by converting CO2 and H2 to CH4 or by
the reduction of sulfur compounds
 Eubacteria
10 Phyla, including cyanobacteria (Autotrophs:
manufacture their own food source)
 First Cells poorly developed metabolic systems
absorbed nutrients directly
fermentation

26. LIFE
 Prokaryota
 Appear 3.8-3.6 by
 no nucleus
 single loop chromosome with all genes
 reproduction-binary fission
 Eukaryota
 Single cell appear 2 by
 Multicellular appear as trace fossils 1by and as body fossils
700my
 Nucleus with 2 pairs of chromosomes (2 copies of all genes)
 Asexual and SEXUAL reproduction>> more combinations

27. HOW DID LIFE ORIGINATE?
 Living things (even ancient organisms like
bacteria) are enormously complex.
 Instead life almost certainly originated in a
series of small steps, each building upon the
complexity that evolved previously:
1. Simple organic molecules were formed.

28.  Simple organic molecules (nucleotide)- the
building blocks of life.
 Experiments suggest that organic molecules
could have been synthesized in the atmosphere of
early Earth and rained down into the oceans.
 RNA and DNA molecules — the genetic material
for all life — are just long chains of simple
nucleotides.

29.  2. Replicating molecules evolved and began
to undergo natural selection.
All living things reproduce, copying their genetic
material and passing it on to their offspring.
 Thus, the ability to copy the molecules that
encode genetic information is a key step in the
origin of life — without it, life could not exist.
 This ability probably first evolved in the form of
an RNA self-replicator — an RNA molecule that
could copy itself.

30.  Many biologists hypothesize that this step led to
an "RNA world" in which RNA did many jobs,
storing genetic information, copying itself, and
performing basic metabolic functions.
 Today, these jobs are performed by many
different sorts of molecules (DNA, RNA,
and proteins, mostly), but in the RNA world,
RNA did it all.

31. 3. Replicating molecules became enclosed within a cell
membrane.
The evolution of a membrane surrounding the genetic material
provided two huge advantages: the products of the genetic
material could be kept close by and the internal environment
of this proto-cell could be different than the external
environment.

32.  4. Some cells began to evolve modern
metabolic processes and out-competed
those with older forms of metabolism.
 everything changed when some cell or group of
cells evolved to use different types of molecules
for different functions: DNA (which is more
stable than RNA) became the genetic material,
proteins (which are often more efficient
promoters of chemical reactions than RNA)
became responsible for basic metabolic reactions
in the cell, and RNA was demoted to the role of
messenger, carrying information from the DNA
to protein-building centers in the cell.

33.  Cells incorporating these innovations would have
easily out-competed "old-fashioned" cells with
RNA-based metabolisms, hailing the end of the
RNA world.
 5. Multicellularity evolved.
 As early as two billion years ago, some cells
stopped going their separate ways after
replicating and evolved specialized functions.
 They gave rise to Earth's first lineage of
multicellular organisms, such as the 1.2 billion
year old fossilized red algae.

34. BOOK AND WEB REFERENCES
 Book Name : 12th
Std NCERT
 http://en.wikipedia.org/wiki/Abiogenesis
 http://www.livescience.com/13363-7-theories-
origin-life.html
 http://education-portal.com/academy/lesson/the-
origin-of-life-on-earth-theories-and-
explanations.html

35. IMAGES REFERENCES
 1.http://d2hh5u5wjpwmol.cloudfront.net/wp-
content/uploads/2011/03/universe.jpg
 2.http://upload.wikimedia.org/wikipedia/common
s/4/48/Planet_formation.jpg
 3.http://bekarice.com/wpcontent/uploads/2014/07/
spontaneous-generation.jpg
 4.https://encryptedtbn1.gstatic.com/images?
q=tbn:ANd9GcR1b_XWavXhz_GyL64OOa3ylkaw
CKXVta2rctLCcA_zxHa_UhRF
 5.http://users.rcn.com/jkimball.ma.ultranet/Biolo
gyPages/M/Miller.gif