Origin of Life Theories
1. Early Earth
• Formed ~4.8 billion years ago
• Collision of particles in space
• Atmosphere :hot, inhospitable; Water
vapor,carbon dioxide and nitrogen,
hydrogen cyanide, hydrogen sulfide,
carbon monoxide--NO OXYGEN
• ~3.8 b.y.a.- cooled, atmosphere
condensed, water remained liquid
(formation of oceans)
2.Primordial soup theory continued
• 1930’s: A.I. Oparin proposed gases in
early Earth combined through chemical
reactions to form organic molecules
needed for life due to energy from the sun,
volcanoes and lightning. Rain probably
washed molecules into oceans.
• 1953: Stanley Miller & Harold Urey’s
experiments provide first evidence for
Oparin’s hypothesis
Figure 17-8 Miller-Urey Experiment
Section 17-2
Mixture of
gases
simulating
atmospheres
of early Earth
Spark
simulating
lightning
storms
Condensation
chamber
Water
vapor
Cold
water
cools
chamber,
causing
droplets
to form
Liquid containing
amino acids and
other organic
compounds
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Section:
3. Protocells
• Scientists suggest microspheres may have
formed
• 1950’s Sydney Fox produced protocells
(microspheres)
• Microspheres have a semi-permiable
membrane & a way of storing/releasing
energy
4. Evolution of Cells
• 3.5 b.y.a. prokaryotic organism
(anaerobic)
• 2.2 b.y.a. oxygen releasing organisms
• Free oxygen drives evolution of aerobic
organisms
• Endosymbiotic Theory proposes that
eukaryotic cells arose from communities of
prokaryotic cells.
Figure 17-12 Endosymbiotic
Theory
Section 17-2
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Plants and
plantlike
protists
Photosynthetic
bacteria
Mitochondrion
Primitive Photosynthetic
Eukaryote
Ancient Anaerobic
Prokaryote
Go to
Section:
Primitive Aerobic
Eukaryote
Animals, fungi, and
non-plantlike protists
Concept Map
Section 17-2
Evolution of Life
Early Earth was hot; atmosphere contained poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the oceans..
Small sequences of RNA may have formed and replicated.
First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.
Later prokaryotes were photosynthetic and produced oxygen.
An oxygenated atmosphere capped by the ozone layer protected Earth.
First eukaryotes may have been communities of prokaryotes.
Multicellular eukaryotes evolved.
Sexual reproduction increased genetic variability, hastening evolution.
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Section: