THEORIES ON HOW LIFE CAME ABOUT

1. PREBIOTIC EVOLUTION
By: Alizay
BS MICROBIOLOGY AND
MOLECULAR GENETICS
THE WOMEN UNIVERSITY MULTAN

2. • Evolution, as the term is used here, signifies any
development or change adapting to the
environment.
• Prebiotic Evolution refers to evolution before
life, describing ideas about how life
began from a ‘prebiotic soup’.

4. CONDITIONS ON EARTH BEFORE
• Earth’s early atmosphere
probably contained hydrogen
cyanide,carbon dioxide,
carbon monoxide,
nitrogen,hydrogen sulfide, and
water.
• Volcanic activity probably
formed it. Released great
amounts of water vapor that
later condensed to form
oceans.
• Released CO2 that warms the
atmosphere by absorbing
outgoing heat.

5. • A common theme is that the ingredients for
life were generated by the flow of energy
(sunlight, lightning, or thermal
radiation) through the primordial
hydrosphere so that the putative
mechanisms for the origin of life should be
compatible with the conditions that would
have prevailed in the early atmosphere and
oceans.

6. How life came about?
FOSSIL EVIDENCE HYDROTHERMAL VENTS
• However, evidence of
extant organisms
appears in fossilized
stromatolites in Western
Australia from 3.5
billion years ago,
suggesting that the
appearance of life
occurred quite rapidly
on a geologic time scale
once the conditions
were favourable
• These vents release important
hydrogen-rich Molecules
Mineral catalysts could have
critical reactions occurs faster

7. CLAY PANSPERMIA
• Clay may have provided the
foundation for first organic
compounds.
• Mineral crystals in clay could
have arranged organic
compounds into organized
patterns.
• Life could have come from
outer space in a comet or
meteorite.

8. ELECTRIC SPARK
• A historic demonstration of
the feasibility of
prebiotic simulations was
performed by Stanley Miller
during the fall of 1952 in the
laboratory of Harold Urey at
the University of Chicago
• They theorized that electric
spark can generate amino
acids and sugars from an
atmosphere loaded with water,
methane, ammonia
and hydrogen

9. OPARIN-HALDENE THEORY (Primordial
Soup Theory)
• Oparin reasoned that O2
prevents the synthesis of
certain organic compounds
that are necessary building
blocks for the evolution of Life
• Oparin proposed that the
"spontaneous generation of
life" did in fact occur once, but
was now impossible because
the conditions found on the
early Earth had changed
• Oparin argued that a
"primeval soup" of organic
molecule could be created in
an oxygen-less atmosphere.

11. BIOGENESIS
Biogenesis states that every living thing came
from a pre-existing living thing.
In 1668 Francesco Redi, proved that no maggots
appeared in
meat when flies were prevented from laying eggs.
In 1768, Lazzaro Spallanzani demonstrated that
microbes were present in the air, and could be killed
by boiling.
In 1861, Louis Pasteur performed a series of
experiments which demonstrated that organisms
such as bacteria and fungi do not spontaneously
appear in sterile, nutrient-rich media.

15. Appearance of oxygen
• About 2.7 b.y.a., cyanobacteria or blue-
green algae began photosynthetic reactions
• About 1.8 b.y.a, the atmosphere contained
abundant free oxygen.
• Allowed for the development of more complex,
oxygen-breathing life forms
• Caused the first mass extinction of organism
that had evolved in an oxygen-less planet
• Ended the process of chemical
• evolution

16. Spirulina

17. Physical Structures That May Have
Given Rise To The First Cells
• Cell like structures, including microspheres
and coacervates, form spontaneously in
certain kinds of solutions.
• Polysaccharides form coacervates in solution.
▫ Membrane-like boundary
▫ Act like cells
▫ Absorb molecules and release products
▫ Form new spheres by budding

18. ENDOSYMBIOTIC THEORY
According to the endosymbiotic theory, eukaryotic cells
formed from a symbiosis among several different prokaryotic
organisms.

19. RNA-World Hypothesis
• RNA is a complex molecule found in all living
things that seems to be able to catalyze its own
reproduction.
• According to this "RNA World" hypothesis, RNA
was the crux molecule for primitive life and only
took a backseat when DNA and proteins—which
perform their jobs much more efficiently than
RNA—developed.

20. • But the RNA World hypothesis doesn't explain
how RNA itself first arose. Like DNA, RNA is a
complex molecule made of repeating units of
thousands of smaller molecules called
nucleotides that link together in very specific,
patterned ways.
• While there are scientists who think RNA could
have arisen spontaneously on early Earth, others
say the odds of such a thing happening are
astronomical.

21. Cyanide
• John Oro at the University of Houston in 1960
made a startling observation: adenine, a
constituent of RNA as well as the nicotinamide
and flavin cofactors, was formed after acid
hydrolysis of ammonium cyanide solutions,
which were deemed prebiotic starting materials
based on the prior detection of HCN in the
Miller-Urey electric discharge reactions

23. • HCN oligomerization also provides a
source of the RNA component, uracil, which
was first identified in such a mixture by Alan
Schwartz and Andries Voet at the University of
Nijmegen