Origin of Life
AP & Pre-AP Biology
Serrano High School
History of Life on Earth
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4.5 billion years ago – origin of Earth
3.8 billion years – age of oldest rock
3.5 billion years – age of oldest fossil
2.7 billion years ago – O2 began to accumulate
2.1 billion years ago – eukaryotic life began
543 million years ago – Cambrian explosion of
animal life
65 million years ago – extinction of dinosaurs
Origin of Life – 4 Stage
Hypothesis
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Abiotic synthesis of small organic
molecules
Abiotic synthesis of polymers
Origin of self-replicating molecules
Origin of protobionts
Origin of Life – 4 Stage
Hypothesis
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Abiotic synthesis of small organic
molecules
Oparin & Haldane – 1920’s
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Conditions on primitive Earth favored abiotic
synthesis
Atmosphere
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Contained less O2
Less oxidizing
More reducing
Origin of Life – 4 Stage
Hypothesis
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Abiotic synthesis of small
organic molecules
Miller & Urey – 1953
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Tested Oparin & Haldane’s
hypothesis
Created conditions of primitive
Earth in lab
Used atmosphere of H2O, H2,
CH4, and NH3
Added spark
Created organic matter
Origin of Life – 4 Stage
Hypothesis
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Abiotic synthesis of polymers
Scientists observed abiotic polymerization
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Dripped solution of monomers on hot sand & clay
Heat vaporized water
Some monomers bonded together
Metal ions (Fe) could have acted as catalysts
Origin of Life – 4 Stage
Hypothesis
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Origin of Self-Replicating
Molecules
Inheritance
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Based on self-replicating
molecules
Way to pass on instructions
for making molecules
Today – DNA
DNA very stable
Origin of Life – 4 Stage
Hypothesis
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Origin of SelfReplicating Molecules
RNA
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May have been 1st
hereditary molecule
May have been 1st
enzymes
Origin of Life – 4 Stage
Hypothesis
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Origin of Self-Replicating Molecules
Molecular replication in RNA world
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In lab, copied short segments of RNA
Zinc acted as catalyst
1980’s discovered RNA could act as enzyme
(ribozymes)
Origin of Life – 4 Stage
Hypothesis
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Origin of Self-Replicating Molecules
Natural selection in RNA world
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RNA shape varies
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Has a genotype – nucleotide sequence
Has a phenotype – shape of molecule
RNA molecules must compete for monomers to
replicate
Molecules that replicate faster & better suited
prevailed (survived)
Origin of Life – 4 Stage
Hypothesis
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Origin of Protobionts
Aggregates of abiotically produced molecules
Internal chemistry different from external
Not capable of precise replication
In lab, protobionts can form spontaneously