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Life on Earth
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Early Earth
What was Early Earth like?
Scientific Theories about evolution of organic
molecules
Chemicals before cells
Pasteur/Virchow, Oparin, Urey/Miller
Biochemical studies
Search for evidence
Early Earth
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Origins of Universe
10-20 billion yrs old
Big Bang
Expanding ever since
Some parts condensed to form Solar Systems or
groups of solar systems called Galaxies
Earth about 4.5 billion yrs old: most /all of the
elements we know today had formed
What was Early Earth like?
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Clouds of water vapour originally surrounding
Earth,condensed to form oceans and seas, still HOT!
One/two large land masses – Pangaea
Volcanoes spewed ash and lava
Atmosphere: gases Hydrogen, carbon monoxide, carbon
dioxide (lots), methane, ammonia, nitrogen BUT NO
OXYGEN
Electrical storms and cosmic rays produced explosive
energy able to penetrate THIN atmosphere
CARBON (organic) compounds managed to originate in
this hostile environment, 4 billion yrs ago
Once biological chemicals were present, primitive
cells emerged about 3.5 billion yrs ago.
Scientific Theories about the
evolution of organic molecules
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SPONTANEOUS GENERATION: people
thought life arose from non-living matter.
 They ‘saw’ maggots appear in rotting meat,
frogs arise from moist earth and fish from
muddy water.
 Not scientifically tested until 1668 – Redi
demonstrated that the maggots in decaying
meat came from eggs laid by flies fig 3.2.1
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100yrs later- Spallanzani : microorganisms
that appeared in broth came from air (but
this could not EXCLUDE spontaneous
generation) fig 3.2.2
 100 yrs later 1862- Louis Pasteur convinced
people that Spontaneous Generation did
NOT occur fig 3.2.3
Chemicals before Cells
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Pasteur / Virchow and others stated that
“All life comes from pre-existing life”
 1923 Oparin: ‘before living things could
arise, living chemicals must be formed”
 He believed gases in primitive atmosphere
could be converted ito molecules of
biological chemicals
 NOT tested until 1950’s by Urey+ Miller
Urey – Miller
Experiment
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Simulated conditions of early earth
and to test for biological chemicals
Fig 3.2.4
Set up apparatus containing gases- hydrogen, methane,
ammonia and water vapour.
Gases were circulated between lower chamber of water
(‘oceans’) and upper chamber (‘atmosphere’)
Electrical discharge passed through atmosphere chamber to
simulate energy in early atmosphere
Samples withdrawn from fluid and atmosphere chambers
contained amino acids and other organic molecules!!
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Further experiments: used UV light instead
of electricity and this produced nitrogenous
bases, ribose, nucleotides and amino acids.
 It did NOT prove conclusively however, the
origin of life but DID prove it was possible
for non-living matter to produce living
matter and this Chemosynthetic Origin of
Life is believed by most biologists today.
Chemicals from Outer Space
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NO concrete evidence that chemicals came
from outer space
 However, carbon has been detected on other
planets, meteorites and comets and floating
freely in giant space clouds.
 Meteorites found on Earth contain organic
chemicals such as Amino acids and what
appears to be fossils.
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Significance of
Chemosynthetic and Outer
Space theories
Universe began
 protons, neutrons + electrons + hydrogen
present
 specific conditions (heat and pressure)
 other elements formed
 simple compounds form
Biochemical Studies
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All living organisms contain same type of basic
chemicals eg Amino acids and sugars
 Most elements and many simple compounds:
hydrogen sulfide, ammonia, methane, water –
existed for 6 billion yrs at least but NO biological
chemicals
 Nonliving (early compounds) before biological
compounds (chemosynthetic theory) or came from
Outer space as ready made cells???
Search for Evidence
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Most experiments try to replicate evolution of
chemicals (Urey-Miller)
 Search Outer space for more living matter
 All scientists agree that for living matter to evolve,
the chemicals of life must be present first for them
to then become organised into cells.
 Evolution from a cellular state to present day life
forms took long periods of time therefore
chemicals must have evolved before first cells
appeared