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

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

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

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

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

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

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

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

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)

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)

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