1. AP & Pre-AP Biology Serrano High School
Origin of Life
AP & Pre-AP Biology
Serrano High School

2. History of Life on Earth
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

3. Origin of Life – 4 Stage Hypothesis
Abiotic synthesis of small organic molecules
Abiotic synthesis of polymers
Origin of self-replicating molecules
Origin of protobionts

4. Origin of Life – 4 Stage Hypothesis
Abiotic synthesis of small organic molecules
Oparin & Haldane – 1920’s
Conditions on primitive Earth favored abiotic synthesis
Atmosphere
Contained less O2
Less oxidizing
More reducing

5. Origin of Life – 4 Stage Hypothesis
Abiotic synthesis of small organic molecules
Miller & Urey – 1953
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

6. Origin of Life – 4 Stage Hypothesis
Abiotic synthesis of polymers
Scientists observed abiotic polymerization
Dripped solution of monomers on hot sand & clay
Heat vaporized water
Some monomers bonded together
Metal ions (Fe) could have acted as catalysts

7. Origin of Life – 4 Stage Hypothesis
Origin of Self-Replicating Molecules
Inheritance
Based on self-replicating molecules
Way to pass on instructions for making molecules
Today – DNA
DNA very stable

8. Origin of Life – 4 Stage Hypothesis
Origin of Self-Replicating Molecules
RNA
May have been 1st hereditary molecule
May have been 1st enzymes

9. Origin of Life – 4 Stage Hypothesis
Origin of Self-Replicating Molecules
Molecular replication in RNA world
In lab, copied short segments of RNA
Zinc acted as catalyst
1980’s discovered RNA could act as enzyme (ribozymes)

10. Origin of Life – 4 Stage Hypothesis
Origin of Self-Replicating Molecules
Natural selection in RNA world
RNA shape varies
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)

11. Origin of Life – 4 Stage Hypothesis
Origin of Protobionts
Aggregates of abiotically produced molecules
Internal chemistry different from external
Not capable of precise replication
In lab, protobionts can form spontaneously