Evolution PPT Biology Class 12

 Page 1


EVOLUTION
Page 2


EVOLUTION
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 W ay galaxy , earth was supposedto
have been formed about 4.5 billion years back.
Page 3


EVOLUTION
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 W ay galaxy , earth was supposedto
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.
? W ater 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 H
2
escaped.
? Oxygen combined with ammonia and methane to form water ,  
CO
2 
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.
Page 4


EVOLUTION
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 W ay galaxy , earth was supposedto
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.
? W ater 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 H
2
escaped.
? Oxygen combined with ammonia and methane to form water ,  
CO
2 
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 ‘killedyeast’.
? This disproved the theory of spontaneous generation.
Page 5


EVOLUTION
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 W ay galaxy , earth was supposedto
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.
? W ater 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 H
2
escaped.
? Oxygen combined with ammonia and methane to form water ,  
CO
2 
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 ‘killedyeast’.
? This disproved the theory of spontaneous generation.
Oparin – Haldane theory of origin of life:
? 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 –
? High temperature.
? V olcanic storms.
? Reducing atmosphere containing CH
4
, NH
3
etc.
?
? In 1953, S.L. Miller an American Scientist created similar conditions in a  
laboratory scale.
? He created electric discharge in a closed flask to raise temperature upto 800oC as
it was in primitive earth.
? Used CH
4 
H
2
, NH
3 
and water vapor inside theflask.
? He observed the formation of amino acids.