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• Speciation – process by which new species arrive.
• Macroevolution – evolution on a grand scale
• Adaptive radiation - evolution of many diversely adapted species from a common ancestor
Chapter 26: Early Earth and the Origin of Life
• Introduction to the History of Life• The Origin of Life
•Organic (Chemical) Evolution
• Major Lineages of Life
Introduction to the History of Life
• Conditions on early Earth• Four Stage Hypothesis of Origin• RNA, the first genetic material• Natural selection’s role – directed
evolution
• Four Stage Hypothesis of Origin
1. Abiotic synthesis of building blocks
2. Production of organic polymers3. Origin of self-replicating molecules
(making inheritance possible)4. Protobionts are packaged with
material that makes internal chemistry different from surroundings
Conditions on early Earth
• Age of Earth is ~4.6 billion years
• Atmosphere had little free O2
• Included CO2, H2O, CO, H2, N2
•Maybe also NH3, H2S, CH4
•Lack of oxygen meant that the environment would have “reducing” nature
What is needed for life to evolve?
• Requirements for chemical evolution to produce life•Absence of oxygen•Energy•Chemical building blocks•Sufficient time
Abiotic synthesis of building blocks: a testable hypothesis
• 1920s – A.I. Oparin and J.B.S. Haldane
• 1953 – Stanley Miller and Harold Urey test the Oparin-Haldane hypothesis
Production of organic polymers
•Other hypotheses:• “hot rocks” – organic molecules are
concentrated as water evaporates from geothermal activity
• Clay – clay contains charged particles which retains organics when runoff is collected
• Deep sea vents produce many inorganic catalysts that could aid in the making of polymers
The RNA World
•Self-replicating RNA molecules•Function as both enzyme and substrate for replication
• Ribozyme is enzymatic RNA•First step in evolution of theDNA / RNA / protein system
Protobionts - similar to cells
• Separate internal environment from external surroundings by a biological membrane• As protobionts became more similar to cells they
would have evolved the following:• Binary fission• Homeostasis• Catalytic activity
Two types of Protobionts
• Microspheres•Formed from water and polypeptides•Electric gradient on surface•Selective permeability
• Liposomes•Lipids organized into a molecular bilayer•Selective permeability•Behave dynamically – grow, split, etc.
Directed evolution
• Large pool of RNA molecules with different sequences
• Selected for ability to catalyze a reaction
• Amplify / mutate / repeat
• In the RNA world, ribozymes catalyzed protein synthesis
• DNA formed from double strands of RNA• DNA more stable than RNA
The first cells
• Heterotrophs that feed on organic molecules
• Anaerobic fermentation process to obtain energy
The First Autotrophs
• Organic molecule food stock became scarce
• Photosynthetic production of organic molecules
• Cyanobacteria evolved later and could split water molecules which released oxygen
The First Aerobes
• More efficient energy production using oxygen respiration
• Significant oxygen in the atmosphere-2 bya
Formation of the Ozone Layer
• Ultraviolet radiation forms O3 from O2 in the upper atmosphere
• Prevents UV from reaching Earth• Enabled organisms to live in surface
waters and on land
Eukaryotes Arose from Prokaryotes
• Endosymbiont theory•Mitochondria and chloroplasts derived from prokaryotes
•Ingested but not digested•Reproduced along with host cell
Major Lineages of Life
• Linnaeus’ two-kingdom system•Plant (non-moving) and Animal (moving)
• Robert Whittaker’s five-kingdom system•Plantae, Animalia, Fungi, Protista, Monera
• Carl Woese’s three-domain system•Eukarya, Archaea, Bacteria
Key Periods in the History of Earth
Glaciations; mammals increased; humans
Mammals diversified; grasses
Aquatic reptiles diversified; flowering plants; mass extinction
Dinosaurs diversified; birds
Dinosaurs; small mammals; cone-bearing plants
Reptiles diversified; seed plants; mass extinction
Reptiles; winged insects diversified; coal swamps
Fishes diversified; land vertebrates (primitive amphibians)
Land plants; land animals (arthropods)
Aquatic arthropods; mollusks; vertebrates (jawless fishes)
Marine invertebrates diversified; most animal phyla evolvedAnaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life
Cenozoic
Mesozoic
Paleozoic
PrecambrianTime
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
1.8–present
65–1.8
145–65
208–145
245–208
290–245
363–290
410–363
440–410
505–440
544–505
650–544
Key EventsEra Period Time(millions of years ago)
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