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The Origin
and Early
Evolution of
Life
Chapter 18
Learning Objectives
1.
2.
3.
4.
Differentiate between chemical evolution and
organic evolution.
Describe the conditions on the primitive earth
predicted by laboratory experiments that favored
the spontaneous development of organic
molecules.
Explain the probable sequence in the origin of the
first cells, and describe how this cell interacted with
its environment.
Review the theories proposed to explain the origin
of eukaryotic organelles.
The Big
Bang
• 12-15 billion years ago all
matter in the universe was
compressed into a mass
the size of our sun
• Sudden instantaneous
explosion of matter and
energy throughout the
known universe
p. 288
• About 4.6 to 4.5 billion years ago
• Minerals and ice orbiting the sun
started clumping together
• Heavy minerals moved to Earth’s
interior, lighter minerals floated to
surface
– Produced outer crust and
inner mantle
• Chemical evolution produced the
primordial sea and the early
atmosphere that would support
the biosphere of the future.
Earth Forms
Earth Is “Just Right” for Life
The Planet:
Early Atmosphere:
• If smaller in diameter,
gravity would not be great
enough to hold onto
atmosphere
• Hydrogen gas
• If closer to sun, water
would have evaporated
• If farther from sun, water
(the solvent of life) would
have been locked up as
ice
• Nitrogen
• Carbon monoxide
• Carbon dioxide
• No gaseous oxygen
p. 288
Stanley Miller’s Experiment
• Mixed methane,
hydrogen, ammonia,
and water
• Simulated lightning
• Amino acids and
other small
molecules formed
electrodes
to
vacuum
pump
CH4
NH3
H2 O
H2
spark
discharge
gases
water out
condenser
water in
What, at a minimum, is
needed to form a cell-like
structure from these
molecules?
p. 289
water droplets
boiling water
water containing
organic compounds
liquid water in trap
Possible Sequence
p. 291
Why is RNA
believed to
be the first
genetic
information?
Why is DNA
a better
molecule for
heredity?
START:
membrane-bound proto-cells
living cells
END
“Organic Evolution”
self-replicating system enclosed in a
selectively permeable, protective lipid sphere
DNA
RNA
formation of
protein-RNA systems,
evolution of DNA
enzymes and
other proteins
formation of
lipid spheres
spontaneous formation of lipids,
carbohydrates, amino acids, proteins,
nucleotides under abiotic conditions
informational molecules
separation of environments
“Chemical Evolution”
The First Cells
• Prokaryotic heterotrophs
Describe what this means.
• Secured energy through
anaerobic metabolism
…Describe.
– No oxygen present
…Why not?
Is there fossil evidence for
these first cells?
p. 291
Fossil Evidence
• photosynthetic eubacteria
• Oxygen producing
• permits aerobic respiration
3.5 bya
p. 292
2.1 bya
1.2 bya
Possible Origin of
ER & Nuclear Envelope
DNA
infolding of plasma membrane
aka: Autogenous Theory
p. 294
Endosymbiotic Theory
p. 295
Cyanophora paradoxa