Evolution Unit

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Evolution Unit

• Chapter 14 The History of Life

What do scientists think it was like on Earth
billions of years ago? Where conditions different
than they are today? What were the first life
forms?
http//www.cosmic-art.co.uk/graphics/earlyearth.jp
g
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I. Biogenesis vs Spontaneous Generation

• How did Scientist prove that spontaneous
  generation did not occur?
• Experiments by
• Francesco Redi (1626-1697)
• Lazzaro Spallanzani (1729-1799)
• Louis Pasteur (1822-1895)

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Redis Experiment

• Most people believed maggots spontaneously
  generated from rotting meat.
• Redi began to study maggots, noticed the
  different developmental stages of flies.
• Experiment- net covered meat that kept adult
  flies away had no maggots. Control jar- had
  maggots.
• Result- many
• people no longer
• supported
• spontaneous
• generation.

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Vital Force Microbes

• The microscope was invented about the time Redi
  did his experiment.
• Scientists then thought these simple life forms
  arose spontaneously from- vital force in the
  air.
• Spallanzani set up
• an experiment to test
• spontaneous generation
• of microbes.

http//www.jasa.net.au/images/peopled.htm
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• Spallanzanis Experiment Broth was heated in
  both experimental control flask.Immediately
  sealed experimental flask.
• Result No growth in sealed flask.
• Spallanzani concluded that growth occurred only
  if microorganisms from the air contaminated it.
• Opponents- said he
• had destroyed the
• vital forcewith heat.

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Pasteurs Experiment

• By mid- 1800s- sp. generation debate was fierce.
• Paris Academy of Science offered prize if an
  experiment could prove one side.
• Pasteur made a curve neck flask- that would
  prevent microbes, but not air, from entering
  flask.
• Boiled flask- no growth. If neck broken growth.
• Pasteur won the prize ended the debate.

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II. Earths History

• 1. The Formation of the Earth
• About 5 billion years ago, solar system was
  probably a swirling mass of gas dust.
• Earth formed by collisions gravitational pull
  of debris?
• 2. Earths Age
• Estimates of about 4 billion years old.
• How did scientists come up with this since it was
  so long ago?
• Sedimentary rock layers
• Radiometric dating

http//www.aerospaceweb.org/question/astronomy/q02
47.shtml
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3. First Organic Compounds

• Early Earths atmosphere Probably had an
  atmosphere with CO2 (similar to Venus) and
  compounds like ammonia( NH3) hydrogen gas (H2),
  water vapor (H20) and methane (CH4)
• Reducing atmosphere
• Todays Atmosphere Contains 21 oxygen
  probably from photosynthesis.
• Oxidizing Atmosphere
• Alexander Oparin(1894-1980)- hypothesis that
  First Simple Organic Compounds- may have been
  able to form in oxygen free atmosphere.

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Miller/Urey Experiment

• By the 1950s, scientists were in hot pursuit of
  the origin of life.
• What kind of environment would be needed to allow
  life to begin?
• In 1953, Stanley L. Miller and Harold C. Urey,
  working at the University of Chicago, conducted
  an experiment that tested Oparins hypothesis
• They took molecules which were believed to
  represent the major components of the early
  Earth's atmosphere and put them into a closed
  system, added lightening
• Results could synthesize organic compounds

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• Gases used were 1. methane (CH4), 2.
  ammonia(NH3) 3. hydrogen (H2), and water (H2O).
• Ran electric current through to simulate
  lightning storms (believed to be common on the
  early earth.)
• Observed that as much as 10-15 of the carbon was
  now in the form of organic compounds. 2 of
  carbon formed some of the amino acids which make
  proteins.

http//www.chem.duke.edu/jds/cruise_chem/Exobiolo
gy/miller.html
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Other theories

• There is a lot of controversy about whether the
  early earth atmosphere was really as reducing
  (enough that amino acids could be produced) as
  Miller/Urey made their experiment. Probably too
  extreme.
• Some scientists hypothesize that organic
  compounds could have been carried to Earth by
  debris from space on Meteorites
• ( the Earth was frequently impacted and organic
  compounds could have accumulated this way)

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How did science explain molecule to cell jump?
Some ideas

• Spheres of proteins organized as membrane
• Microspheres
• Droplets which contain organic molecules
• Coacervate
• These do not have the properties of life.

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What came 1st- The cell, the DNA or the RNA?

• RNA may have been first.
• RNA may act as enzymes, templates, can self-
  replicate.
• Early cells may have been the basis for early
  cell genetics.

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The First Cells

• Early Earth conditions
• little or no Oxygen available,
• many organic molecules
• Have some fossils that seem to be the same size
  shape of bacteria
• Lack direct evidence, but the list supports the
  idea that the first
• cells were probably
• ANAEROBIC
• HETEROTROPHIC
• PROKARYOTIC

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PHOTOSYNTHESIS

• Some forms of life probably became photosynthetic
  due to competition about 3 billion years ago.
  (like cyanobacteria)
• Oxygen, a by-product of photosynthesis was
  damaging to anaerobic organisms
• Bonding Oxygen was probably an early function of
  areobic respiration.
• May have taken a billion years for oxygen to
  reach current atmospheric levels.

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The First Eukaryotic Cells

• Endosymbiosis- the theory that a small aerobic
  prokaryotic cell was engulfed by a larger
  anaerobic prokaryote and began to live
  reproduce inside it.
• Evolved into modern mitochondria, or chloroplasts
  other organelles.