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Hypothetical Steps in the origin of simple cells
- Abiotic synthesis of small organic molecules
- • Amino acids, nucleotides
- 2. Joining small molecules into macromolecules
- • Proteins, nucleic acids
- 3. Packaging of molecules into protobionts (25.3)
- • Droplets of macromolecules within membranes
- 4. Origin of self-replicating molecules
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Miller and Urey Experiments
- Early atmosphere contained ingredients for organic molecules
- •Water vapor, nitrogen compounds, carbon dioxide, sulfur compounds
- –Produced amino acids, sugars, lipids
- • Volcanoes and deep-sea vents also a possible source of energy
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Proposed role of RNA in early life
- RNA can act as enzyme-like catalysts
- –Called ribozymes
- • Some ribozymes can copy RNA
- –Create complementary molecules and/or
- –Capable of self-replication
- –If nucleotide building blocks are present
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Radiometric dating the fossil record
- Based on decay of isotopes (ex. C14->C12)
- –Fossils contains unstable isotope from the organism when it was alive
- –Over time the unstable isotope decays
- –The amount of isotope remaining gives age
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Single celled prokaryotic organisms
- First evidence: fossilized stromatolites
- –Layered rocks that form when prokaryotes bind sediment together
- • Prokaryotes are single celled organisms that lack a nucleus and other membrane bounded organelles
- –3.5 billion years ago
- • Simpler organisms probably existed earlier
- • Still produced today by similar organisms
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Photosynthetic Oxygen Production
- Early atmosphere had little oxygen gas
- • Photosynthesis produces oxygen
- –Likely evolved in Cyanobacteria (> 2.7 bya)
- • Gradually oxygen gas levels build up
- –Allowed the evolution of aerobic respiration
- • Evidence: banded iron formations
- –Created by iron oxide
- –Some cyclical variation (seasonal etc.)
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Endosymbiotic hypothesis
Larger cells engulf smaller prokaryotes
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Multicellularity
- First multicellular organisms were likely small algae
- –Ex. Forming filaments or sheets of cells
- • Benefits of being multicellular
- –Larger, more complex organisms
- –Specialization of cells
- • Leads to formation of tissues and organs
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Cambrian Explosion
- period of rapid species diversification
- –~525 mya
- • Prior to this period most animals were:
- –Soft bodied
- –Herbivorous, filter feeders, scavengers
- • Origin of larger predators
- • Simultaneously, defensive features arose
- –Spines, body armor etc.
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Colinization on Land
- Cyanobacteria > 1 bya
- • Larger life forms ~ 500 mya
- –Plants and fungi first, then animals
- • Required adaptations for dehydration
- –Ex. Plant adaptations:
- • Waterproof exterior coating
- • Internal vascular system
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Continental Drift
- Continents move over time
- –Plates of Earth’s crust float over hot mantle
- –Drift a few cm / year
- • Slowly rearrange geography
- • Alters the habitat of organisms
- –Ex. Cold --> warm, wet --> dry
- • Leads to adaptation, speciation, extinction
- –Ex. Allopatric speciation
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Mass Extinctions
- Most species that ever lived are extinct
- • Extinctions caused by:
- –Ex. Habitat destruction
- –Ex. Environmental change
- • Five mass extinctions in fossil record
- –Best observed in hard-bodied sea animals
- –In each event, 50% of marine species extinct
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Adaptive Radiations
- Periods in which many new species form
- • Can occur after mass extinctions
- –Adaptations to new open ecological niches
- • Occur with colonization of “vacant” areas
- –Less natural selection, more variation persists
- –Less competition between species
- • Periods often include major innovations
- –Ex. plants producing seeds
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