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
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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 Diversity
Squid
• Arose in PreCambrian era
• ~1 billion years ago
• Fossils, 610-540
million years ago
• Invertebrates
• Major body plans
formed at Cambrian
period
Ammonites
Trilobites
Nautilus
Invasion of the land
• Adaptations for life on
land:
• Gravity
• Breathing
• Water
• Movement
• Reproduction
Thinking about the chapter
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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?
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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?
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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.
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5. What advantages and disadvantages would terrestrial existence
have had for the first plants to invade the land? For the first land
animals?