3. Original Conditions on Primitive Earth
to make life….
• Presence of liquid water
• Moderate temperature range
• Free oxygen in the atmosphere
• Adequate sunlight
• Absence of toxic substances in atmosphere
• Absence of lethal radiation
4. Volcanoes Play a BIG Role
• Water vapor (eventually condensed and fell as RAIN)
• Methane
• Hydrogen
• Nitrogen
• Ammonia
• Carbon Dioxide (we now have oxygen b/c of photosynthetic
bacteria)
• Carbon Monoxide
5. Earth History
• Evolution is studied using concepts about earth history. The
earth is between 4.3 and 4.5 billion years old.
• Approximately 3.9 billion years ago, the surface was likely
cool enough for water vapor to condense and form oceans
• Geological evidence suggests that cells similar to modern
bacteria were common 3.8 billion years ago.
6. How did life on Earth begin?
Until the 1700’s people believed that living things
could come from nonliving substances, spontaneous
generation.
7. Spontaneous generation: Pasteur’s experiment
• Experiment: Pasteur filled a flask with broth with a long S shaped neck.
He boiled it to kill all life. It was open and exposed to air, but anything in
the air got stuck on the curves of the neck.
• Conclusion: Spontaneous generation was disproved and biogenesis
theory was substantiated. Contamination came from other
microorganisms, not “air”.
QUESTIONS
• What was the hypothesis? What was the experimental group? The
control group? The constants? The variable?
8. Theory of Chemical Evolution
“Primordial Soup Theory”
• Conditions on the early Earth were
very different.
• The atmosphere had no oxygen
• Energy sources, such as lightning, volcanic activity, and ultraviolet
sunlight (no ozone layer)
9. Chemical Evolution
• Earth’s early atmosphere: HCN, CO2, CO, N, H, S, H2O
• “Life arose from the oceans”
• He believed that energy from lightning and the sun can
spark chemical reactions to create AMINO ACIDS that made
proteins.
10. Chemical Evolution
Urey and Miller
• created in the
laboratory, the
conditions of early
Earth.
• They discharged
sparks in an
“atmosphere” of
the Miller-Urey
model consisted of
H2O, H2, CH4, and
NH3 gases.
• produced a variety
of amino acids and
other organic
molecules.
11. Chemical Evolution
• Alternate sites proposed for the synthesis of organic
molecules include
• submerged volcanoes and deep-sea vents where
hot water and minerals gush into the deep ocean.
12. Prokaryotes
• Prokaryotes were the earliest organisms on
Earth and evolved alone for 1.5 billion years.
• two prokaryotic domains:
Bacteria and Archaea
13. Prokaryotes
• have a cell wall external
to the cell membrane
• Lack membrane bound
nuclues and organelles
• Double-stranded DNA
molecule is in a single
ring shaped
14. OXYGEN ATMOSPHERE The evidence of oxygen gas
formation can be seen in rocks
• Remember the atmosphere of early when layers of iron oxide on the
Earth was made up of nitrogen, bottoms of oceans stopped
carbon dioxide, water vapor, but no forming when oxygen appeared.
free oxygen
• Oxygen comes from photosynthesis
when leaving oxygen gas.
• About 2 billion years ago, the oxygen
level in the atmosphere started to
rise. Cyanobacteria created the
oxygen in the atmosphere.
• Aerobic metabolism, much more
efficient than anaerobic, became
possible. Question
What are the reactants in
photosynthesis?
The products?
Notes de l'éditeur
Experimental group: Exposed for 1 year, no microorganismsControl Groups : Removed “S” curve and exposed it for 1 day and microorganisms grewConclusion: Spontaneous generation was disproved and biogenesis theory was substantiated. Contamination came from other microorganisms, not “air”.
