Chapter 26.
Origin of Life
AP Biology
2004-2005
The historical tree of
life can be documented
with evidence.
The Origin of Life on
Earth is another story…
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2004-2005
Origin of Life hypothesis
 Abiotic synthesis of organic molecules

amino acids & nucleotides
 Building polymers
joining molecules into polymers
 proteins & nucleic acids

 Protobionts
packaging polymers into membranebound droplets
 maintain internal chemistry

 Origin of self-replicating molecules

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makes inheritance possible
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Conditions on early Earth
 Reducing atmosphere
electron-adding
 water vapor, CO2, nitrogen, NOx, CH4,
NH3, H2, H2S

 Energy source

lightning, UV radiation, volcanic
What’s
missing from
that atmosphere?!
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2004-2005
Abiotic synthesis
 Testable hypothesis
1920
Oparin & Haldane
propose reducing
atmosphere
hypothesis
 1953
Miller & Urey
test the
hypothesis

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2004-2005
Stanley Miller
University of Chicago
yielded
amino acids
hydrocarbons
N bases
other organic
molecules
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Protobionts
 Life  reproduction & metabolism
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2004-2005
RNA world
 RNA is likely first genetic material
multi-functional molecule
 codes information
 enzyme functions

 ribozymes
 replication
regulatory molecule
 transport molecule

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Dawn
of natural selection
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Key Events in Origin of Life
 Key events in
evolutionary
history of life on
Earth

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life originated
3.5–4.0 bya
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Prokaryotes
 Prokaryotes dominated life
on Earth from 3.5–2.0 bya
3.5 billion year old
fossil of bacteria
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modern bacteria
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Stromatolites
fossilized mats of
prokaryotes
resemble modern
microbial colonies
Lynn Margulis
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2004-2005
Oxygen atmosphere
 Oxygen begins to accumulate 2.7 bya

photosynthetic bacteria
 cyanobacteria (blue-green algae)

reducing  oxidizing atmosphere
 corrosive
 banded iron in rocks = rusting
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Endosymbiosis
 Evolution of eukaryotes

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membrane bound organelles = 2.1 bya
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Cambrian explosion
 543 mya

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within 10–20 million years most of the major
phyla of animals appear in fossil record
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Diversity of life & periods of mass extinction
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The Chicxulub impact crater in the
Caribbean Sea near the Yucatan
Peninsula of Mexico indicates an
asteroid or comet struck the earth and
changed conditions 65 million years ago
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2004-2005
Early mammal evolution
 125 mya mammals
began to radiate
out & fill niches
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Classification
 Linnaeus used structural similarity
 1969
Robert Whittaker devised 5 Kingdom
system
Monera
 Protista
 Plantae
 Fungi
 Animalia

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2004-2005
Re-Classifying Life
 New groupings
molecular data challenges 5 Kingdoms
 Monera is too diverse

 2 distinct lineages of prokaryotes

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Protists are too diverse
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3 Domain system
 Super Kingdoms
Bacteria
 Archaea

 extremophiles = live in extreme environments

Eukarya
 eukaryotes
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2004-2005
1500
2000
PHANEROZOC
2500
3000
3500
PRECAMBRIAN
1000
Bacteria Archae- Protista Plantae Fungi
bacteria
Oldest definite fossils
of eukaryotes
Appearance of oxygen
in atmosphere
Oldest definite fossils
of prokaryotes
4000
Molten- hot surface of
earth becomes somewhat
cooler
4500
Formation of earth
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Animalia
Colonization of land
Paleozoic by animals
Appearance of animals
and land plants
First multicellular
organisms
ARCHEAN
Millions of years ago
500
Cenozoic
Mesozoic
PROTEROZOIC
0
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Kingdom
Bacteria
Kingdom
Archaebacteria
Kingdom
Protista
Kingdom
Fungi
Kingdom
Plantae
Kingdom
Animalia
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2004-2005