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?