CHAPTER 25
CAMPBELL and REECE
Conditions on early Earth
made the Origin of Life
possible
 Macroevolution : evolutionary change above the
species level
 examples:
emergence of terrestrial vertebrates
2. mass extinctions impact on diversity of life
3. origin of key adaptations like flight in birds
1.
Where did 1st cell come from?
 4 main stages could have produced very simple cells:
1. The abiotic synthesis of small organic molecules
2. Joining of these small molecules into
macromolecules (proteins, nucleic acids)
3. Packaging of these macromolecules into
protocells, droplets with membranes that
maintained internal chemistry different from their
surroundings
4. Origin of self-replicating molecules that eventually
made inheritance possible
Synthesis of Organic Cpds
on early Earth
 Planets of our solar
system formed ~ 4.6
billion yrs ago
 1st few hundred million
yrs conditions would
not have allowed life
on Earth
st
1
Atmosphere
 Collisions would have
vaporized any water
preventing seas from
forming
 Atmosphere thick with
gases released from
volcanic activity
1st Atmosphere
 1920’s: Oparin (Russian
chemist) and Haldane
(British scientist) each
came to conclusion
early atmosphere was
reducing environment
(gain e-) in which
organic compounds
could have formed
from simpler
molecules
st
1
Organic Compounds
 Energy sources:
 Lightning
 Thermal energy
 Intense UV radiation
Primordial Soup
 Haldane had hypothesized the early seas site of 1st
organic compounds  1st cells
 Miller & Urey (Univ. of Chicago) in 1950’s
 Tested Oparin & Haldane ‘s premise
 Created a reducing atmosphere
 Added compounds considered to have been found
existing on early earth (hydrogen gas – H2,
ammonia – NH3, methane – CH4, and H2O vapor)

Miller & Urey
 Experiment: In 1953, Stanley Miller set up a closed system to
simulate conditions thought to have existed on early Earth
1. Water mixture in “sea” flask was heated; vapor entered atmosphere flask
2. “Atmosphere” flask contained mix of hydrogen gas, methane, ammonia,
and water vapor (believed to mimic early Earth’s atmosphere)
3. Sparks were discharged to mimic lightning
4. Condenser cooled the “atmosphere”, “raining” water and any dissolved
molecules down into sea flask
5. As material cycled through apparatus, Miller periodically collected
samples for analysis
 Results: Miller identified variety of organic molecules common in
organisms (including simple molecules like formaldehyde (CH2O)
and hydrogen cyanide (HCN) and more complex molecules (like
amino acids and hydrocarbons)
 Conclusion: Organic molecules (a 1st step in the origin of life) may
have been synthesized abiotically on early Earth
Miller & Urey’s Experiment
Miller & Urey’s Results
Miller-Urey
Experiment Clip
Miller & Urey’s Results
 Have been repeated using same or similar
ingredients, different recipes for the atmosphere
and they also produced organic compounds
 Still ?s about amounts of methane, ammonia (was
there really enough to make it a reducing
environment?)
 Some repeated experiment in non-reducing, nonoxidizing conditions & still produce organic
compounds
Miller-Urey Experiment
demonstrates:
1. Abiotic synthesis of organic molecules is
possible under various assumptions about the
composition of Earth’s early atmosphere
2. Meterorites may also have been source of
minerals and organic molecules

Contain amino acids, lipids, simple sugars, uracil
Murchison Meteorite
Murchison Meteorite
 Fell to Earth in so named town in Australia in 1969
 large (100 kg) and was quickly retrieved
 2010 article published in Scientific American:
results of mass spectrometry (separating
compounds based on charge & size) have revealed
at least 14,000 unique molecules
Abiotic Synthesis of
Macromolecules
 2009 study showed the abiotic synthesis of RNA
monomers can occur spontaneously from simpler
precursor molecules
 Drip solutions with amino acids (aa) or RNA
nucleotides onto hot sand, rock, or clay 
polymers of aa & RNA (w/out using enzymes or
ribosomes)
Protocells (Protobionts)
 Basic characteristics of life : reproduction &
metabolism:
 So 1st cells would have had to be able to
reproduce which would have required them
to have a source of nitrogenous bases,
sugars, phosphate groups
 Now complex enzymes make this all happen
Vesicles as
st
1
step?
 When lipids & other organic molecules added to
water  vesicles spontaneously form
 lipid bilayer (separation of hydrophilic &
hydrophobic molecules)
 These abiotically produced vesicles
“reproduce” and grow on their own.
 Clay, like from early Earth will be absorbed
into the vesicles
 some vesicles demonstrate semipermeability
Self-Replicating RNA
 RNA (when folded)can act as
enzyme
 RNA catalysts called: ribozymes
 Some can make
complimentary strands of
short pieces of RNA 
mutations  more stable
&/or successful
Ribozyme
 Once self-replicating
RNA possible much
easier for further
changes to happen.
 Once double-stranded
DNA appeared it
would have been more
stable so RNA left with
role we see today