EVOLUTION
CHAPTER 7 XII BIOLOGY NOTES
ORIGIN OF LIFE:
• Stellar distances are measured in light years.
• The universe is very old – almost 20 billion years old.
• The Big Bang theory attempts to explain to us the origin of universe.
The Big Bang theory:
• A singular huge explosion unimaginable in physical term.
• The universe expanded and hence the temperature came down.
• Hydrogen and Helium formed sometime later.
• The gases condensed under gravitation and formed the galaxies of the present day universe.
• In the solar system of the Milky Way galaxy, earth was supposed to have been formed about 4.5
billion years back.
Condition of early earth:
• Earth formed 4.5 billion years back.
• There was no atmosphere on early earth.
• Water vapor, methane, carbon dioxide and ammonia released from molten mass covered the
surface.
• The UV rays from the sun broke up water into Hydrogen and oxygen and lighter H2 escaped.
• Oxygen combined with ammonia and methane to form water, CO2 and others.
• The ozone layer was formed.
• As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
• Life appeared 500 Million years after the formation of earth.
Origin of life:
• Early Greek thinkers thought units of life called spores were transferred to different planets
including earth.
• ‘Panspermia’ is still a favorite idea for some astronomers.
• For a long time it was also believed that life came out of decaying and rotting matter like straw,
mud etc.This was the theory of spontaneous generation.
Louis Pasteur experiment:
• Careful experimentation demonstrated that life comes only from pre-existing life.
• He showed that in pre-sterilized flasks, life did not come from killed yeast while in another flask
open to air, new living organism arose from ‘killed yeast’.
• This disproved the theory of spontaneous generation.
Oparin – Haldane theory of origin of life:
1
Notes by KC Meena
, • Oparin of Russia and Haldane of England proposed that the first form of life could have come from
pre- existing non-living organic molecule (e.g. RNA, protein etc.).
• Formation of life was preceded by chemical evolution i.e. formation of diverse organic molecule
from inorganic constituents.
Urey and Miller experiment:
• The conditions on earth were –
o High temperature.
o Volcanic storms.
o Reducing atmosphere containing CH4, NH3 etc.
• In 1953, S.L. Miller an American Scientist created similar conditions in a laboratory scale.
o He created electric discharge in a closed flask to raise temperature upto 800oC as it
was in primitive earth.
o Used CH4 H2, NH3 and water vapor inside the flask.
o He observed the formation of amino acids.
Acceptance of chemical evolution theory: (evidences)
• Miller observed the synthesis of amino acids from simple inorganic chemicals in simulated
condition in the laboratory.
• In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.
• Analysis of meteorite content also revealed similar compounds indicating that similar processes are
occurring elsewhere in space.
2
Notes by KC Meena
CHAPTER 7 XII BIOLOGY NOTES
ORIGIN OF LIFE:
• Stellar distances are measured in light years.
• The universe is very old – almost 20 billion years old.
• The Big Bang theory attempts to explain to us the origin of universe.
The Big Bang theory:
• A singular huge explosion unimaginable in physical term.
• The universe expanded and hence the temperature came down.
• Hydrogen and Helium formed sometime later.
• The gases condensed under gravitation and formed the galaxies of the present day universe.
• In the solar system of the Milky Way galaxy, earth was supposed to have been formed about 4.5
billion years back.
Condition of early earth:
• Earth formed 4.5 billion years back.
• There was no atmosphere on early earth.
• Water vapor, methane, carbon dioxide and ammonia released from molten mass covered the
surface.
• The UV rays from the sun broke up water into Hydrogen and oxygen and lighter H2 escaped.
• Oxygen combined with ammonia and methane to form water, CO2 and others.
• The ozone layer was formed.
• As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
• Life appeared 500 Million years after the formation of earth.
Origin of life:
• Early Greek thinkers thought units of life called spores were transferred to different planets
including earth.
• ‘Panspermia’ is still a favorite idea for some astronomers.
• For a long time it was also believed that life came out of decaying and rotting matter like straw,
mud etc.This was the theory of spontaneous generation.
Louis Pasteur experiment:
• Careful experimentation demonstrated that life comes only from pre-existing life.
• He showed that in pre-sterilized flasks, life did not come from killed yeast while in another flask
open to air, new living organism arose from ‘killed yeast’.
• This disproved the theory of spontaneous generation.
Oparin – Haldane theory of origin of life:
1
Notes by KC Meena
, • Oparin of Russia and Haldane of England proposed that the first form of life could have come from
pre- existing non-living organic molecule (e.g. RNA, protein etc.).
• Formation of life was preceded by chemical evolution i.e. formation of diverse organic molecule
from inorganic constituents.
Urey and Miller experiment:
• The conditions on earth were –
o High temperature.
o Volcanic storms.
o Reducing atmosphere containing CH4, NH3 etc.
• In 1953, S.L. Miller an American Scientist created similar conditions in a laboratory scale.
o He created electric discharge in a closed flask to raise temperature upto 800oC as it
was in primitive earth.
o Used CH4 H2, NH3 and water vapor inside the flask.
o He observed the formation of amino acids.
Acceptance of chemical evolution theory: (evidences)
• Miller observed the synthesis of amino acids from simple inorganic chemicals in simulated
condition in the laboratory.
• In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats.
• Analysis of meteorite content also revealed similar compounds indicating that similar processes are
occurring elsewhere in space.
2
Notes by KC Meena
