Abiogenesis

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Abiogenesis the Invisible World

• Science progresses by observation...

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To set the scene...

• Observations are often FLAWED by INTERPRETATIONS
  that attempt to explain what was observed.

• Scientists often propose explanations (hyptheses)
  in an attempt to interpret natural events.

• Hypotheses proposed by early scientists were
  almost never tested by experiment.

• Often, one unsubstantiated hypothesis became the
  basis for another scientists moved further
  further from the truth...

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Aristotle

• Great philosopher of ancient Greece
• Theory of Abiogenesis states that nonliving
  things can be transformed into living things
  spontaneously (sometimes called spontaneous
  generation).
• Aristotles theory was accepted for nearly 2000
  years!

frogs and fish did not fall from the sky but
came from the mud
4
Jean van Helmont

• Only 300 years ago
• concluded that mice could be created from grains
  of rice a sweaty shirt within 21 days
• the sweat in the shirt caused the wheat to
  ferment..
• the bubbling wheat eventually transformed into
  mice

Until now, science had been based on logical
analysis rather than on experimentation.
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Francesco Redi (1668)

• Tested hypothesis that rotting meat could
  transform into flies
• I placed bits of eel, snake, fish, veal in
  four different jars
• open set experimental group
• closed jars control set
• critics claimed that the active ingredient
  (air) was not permitted into the sealed jars
  where no flies appear
• I experimented with fine mesh tops

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A Window on the Invisible World
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Antony van Leeuwenhoek (1632-1723)

• Expert lens maker
• Remarkable observant scientist
• His scopes were the first to reveal
  microorganisms human blood cells!

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Abiogenesis Microbes
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John Needham (1713-1781)

• Re-examined theory of spontaneous generation
• Observed meat broth left unsealed soon changed
  color gave off a putrid smell
• Tested his hypotheses through experimentation
• Boiled flasks with meat broth in LOOSELY sealed
  flasks for a few minutes to kill microbes
• After a few days the murky contents were examined
  under a microscope
• The broth was FULL of microbes!
• Needham rushed to retest the experimentusing
  different types of broths.
• Microbes continued to appear.
• Needham concluded that this was a result of
  spontaneous generation

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Lazzaro Spallanzani (1729-1799)

• 25 years after Needhams experiments
• By prolonging the heat and more carefully sealing
  the vessels, Spallanzani was able to show that
  such broths generated no microorganisms as long
  as the vessels remained sealed.
• Abiogenesis did NOT occur!

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Louis Pasteur (1822-1895)

• The FINAL BLOW to the theory of abiogenesis
• Swan-necked flask
• Boiled broth for a long time
• Microbes became trapped in the curve of the
  glass!

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Emergence of the Cell Theory

• Thats another class! ?