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Chapter 20. The Origin and Evolutionary History of Life. Conditions on early Earth Age of Earth is ~4.6 billion years Atmosphere had little free O 2 Included CO 2 , H 2 O, CO, H 2 , N 2 Maybe also NH 3 , H 2 S, CH 4. Requirements for chemical evolution to produce life Absence of oxygen
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Chapter 20 The Origin and Evolutionary Historyof Life
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
Requirements for chemical evolution to produce life • Absence of oxygen • Energy • Chemical building blocks • Sufficient time
Prebiotic soup hypothesis • Molecules formed near the Earth’s surface • Sugars, nucleotides, amino acids formed spontaneously
Iron-sulfur world hypothesis • Organic molecules formed at hydrothermal vents on the ocean floor • Laboratory simulations show catalyst effects of iron and nickel sulfides
Origin of cells • Spontaneous assembly of small organic molecules into macromolecules • Protobionts similar to cells • Binary fission • Homeostasis • Catalytic activity
Microspheres • Formed from water and polypeptides • Electric gradient on surface • Selective permeability
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
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
Autotrophs • Selected after organic molecule food stock became scarce • Photosynthetic production of organic molecules • Cyanobacteria split water molecules and released oxygen
Aerobes • More efficient energy production using oxygen respiration • Significant oxygen in the atmosphere by 2 bya
Formation of the ozone layer • Ultraviolet radiation forms O3 from O2 in the upper atmosphere • Prevents UV from reaching Earth • Decreased mutagenesis • 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
Geological eras • Paleozoic • 543 mya - 251 mya • Mesozoic • 251 mya - 65 mya • Cenozoic • 65 mya - present
Precambrian time • Before 543 mya • Bacteria • Protists • Fungi • Simple multicellular animals
Cambrian explosion • All animal phyla established • Many new body plans • Bizarre, extinct phyla
Ordovician period • Shallow seas covered land • Cephalopods • Coral reefs • Jawless fishes
Silurian period • Jawed fishes • Terrestrial plants • Air-breathing animals
Devonian period • Bony fishes • Amphibians • Wingless insects • All major plant groups except for flowering plants established
Carboniferous period • Swamp forests • Reptiles • Winged insects
Permian period • Therapsids • Reptilian ancestors of mammals • Seed plants dominant • Ended the Paleozoic with the greatest mass extinction • 90% of marine species • 70% of land vertebrates
Triassic period • Thecodonts • Ancestors of dinosaurs and birds • Pleiosaurs and ichthyosaurs • Pterodonts • First mammals • Small insectivores
Jurassic and Cretaceous periods • Saurischians • Ancestors of lizards • Ornithischians • Ancestors of birds • Ended with mass extinction caused by a meteorite impact
Tertiary period • Diversification of flowering plants, birds, insects, mammals • Quaternary period • Genus Homo • Large mammals