Origin of Life
• How did life begin?• What were the
earliest organisms like?
• Endosymbiosis• Multicellular
organisms?• Invasion of land
Europa, one of Jupiter’s moons
History of Life on Earth
How did life begin?
• Spontaneous generation refuted
• Francisco Redi• Louis Pasteur
Early Earth
• Sources of organic compounds
• Extra-terrestrial sources: meteorites
• Contain amino acids, small amount
• Concentrated in tide pools
Miller & Urey experiment• Closed system• Simulate conditions of early
earth as suggested by Oparin& Haldane
• Sparks for lightning• Identified:• Amino acids, organic acids,
hydrocarbons• Further work has synthesized
all major groups of molecules.• May not have contained
necessary gases• Deep sea vent and volcanos
RNA
• RNA: Two properties• Genetic material, self
replicating• Enzymes: catalytic
function• Ribozymes
Monomer to Polymers• Abiotic synthesis on hot
clay surface• Spontaneous
polymrerization• Protobionts
(microspheres) • Agitation of proteins and
lipids• Steps appear to be
biologically possible and plausible
First Cells
•Anaerobic prokaryote•Heterotrophic•No nucleus•3.5 billion years old•Photosynthetic bacteria evolved•O2 evolving organisms
Endosymbiont Hypothesis
• Formation of Eukaryotic cells
• 2.1 billion years ago• Aerobic bacterium• Evidence for
Mitochondria• DNA • Membranes• Ribosomes• Amoeba with aerobic
bacterium
Plant Cells
Formation of plastids similar to mitochondria
Multicellular organisms
• Colonial organisms, similar cells
• Multicellular algae• Differentiation• Cellular specialization• Division of labor
Animal DiversitySquid Trilobites
Ammonites Nautilus
• Arose in Pre-Cambrian era
• ~1 billion years ago• Fossils, 610-540
million years ago• Invertebrates• Major body plans
formed at Cambrian period
Invasion of the land
• Adaptations for life on land:
• Gravity• Breathing• Water• Movement• Reproduction
Thinking about the chapter • 1. What is the evidence that life might have originated from nonliving
matter on early Earth? What kind of evidence would you like to see before you would accept this hypothesis?
• .• 2. If the first cells with aerobic metabolism were so much more
efficient at producing energy, why didn’t they drive cells with only anaerobic metabolism to extinction?
• .• 3. Explain the endosymbiont hypothesis for the origin of chloroplasts
and mitochondria.• 4. Name two advantages of multicellularity for plants and two
advantages for animals.• .• 5. What advantages and disadvantages would terrestrial existence
have had for the first plants to invade the land? For the first land animals?