Transcript Stage 3: Packaging of polymers into protobionts

Conditions on early Earth made the origin of life
possible
○ Possible composition of Earth’s early atmosphere
– H2O vapor
– N2
– CO2, CH4, NH3,
– H2, and H2S
○ Energy sources
 Lightning, volcanoes, UV radiation
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 Earth formed 4.6 billion years ago
 Oldest fossils are 3.5 billion years old
○ Photosynthetic bacteria in stromatolites
 The first living things are thought to be simpler
and arose much earlier
○
Heterotroph hypothesis
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 1920s
○ Oparin and Haldane
 independently proposed that organic molecules
could have formed on the early Earth
 1953
○ Stanley Miller tested the Oparin-Haldane
hypothesis
– Miller set up an airtight apparatus with gases
circulating past an electrical discharge, to
simulate conditions on the early Earth
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 After a week, Miller’s setup produced abundant
amino acids and other organic molecules
–
Similar experiments used other atmospheres and
other energy sources, with similar results
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Chemical conditions
Stage 1
Stage 2
Stage 3
Stage 4
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Physical conditions
Abiotic synthesis of
monomers
Formation of polymers
Packaging of polymers into
protobionts
Self-replication

Stage 2: The formation of polymers
– Monomers could have combined to form organic
polymers
– Same energy sources
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
Stage 3: Packaging of polymers into
protobionts
– Polymers could have aggregated into complex,
organized, cell-like structures
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 Stage 4: Self-replication
– RNA may have served both as the first genetic
material and as the first enzymes
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Monomers
1 Formation of short RNA
polymers: simple “genes”
2 Assembly of a
Monomers
1 Formation of short RNA
polymers: simple “genes”
complementary RNA
chain, the first step in
replication of the
original “gene”
 A variety of protobionts could have existed on the
early Earth
 Some of these protobionts contained selfreplicating RNA molecules
How could natural selection have acted on these
protobionts?
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