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The History of Life on Earth

The History of Life on Earth. History of Life. Originated 3.5-4.0 billion years ago Fossil evidence: stromatolites. Major Episodes in the History of Life. Prokaryotes-3.6 billion years ago Prokaryotes diverged into Bacteria and Archaea 2-3 billion years ago

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The History of Life on Earth

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  1. The History of Life on Earth

  2. History of Life • Originated 3.5-4.0 billion years ago • Fossil evidence: stromatolites

  3. Major Episodes in the History of Life • Prokaryotes-3.6 billion years ago • Prokaryotes diverged into Bacteria and Archaea 2-3 billion years ago • Photosynthetic bacteria began producing O2 2.5 billion years ago • Eukaryotes emerged 2 billion years ago

  4. Prebiotic Chemical Evolution • Abiotic synthesis and accumulation of monomers • Formation of polymers • Formations of protobionts • Origin of heredity during or before protobiont appearance

  5. Protobionts • Aggregates of abiotically produced molecules • Maintain internal environment, different from surroundings • Exhibit some life properties-irritability and metabolism • Self-assemble • Microspheres and liposomes

  6. Laboratory versions of protobionts

  7. RNA was probably the First Genetic Material • If DNA, a primer would be necessary • RNA can self-replicate • RNA is autocatalytic • Achieves unique tertiary structure (different phenotypes)-diversity!

  8. Abiotic Replication of RNA

  9. If Protobionts: Incorporated genetic information Selectively accumulated monomers Used enzymes programmed by genes to make polymers Grew and split Then: Variations would lead to natural selection Refinements would have accumulated Lead to the appearance of DNA Hereditary Material Enabled Darwinian Evolution

  10. Videos and Websites • http://www.youtube.com/watch?v=zufaN_aetZI&feature=fvw • http://www.youtube.com/watch?v=OandUMjhZ3g&NR=1&feature=fvwp

  11. The Fossil Record and Geologic Time • Role of sedimentary rocks • Fossil dating, use of strata location vs. absolute dating • Fossil record incomplete, favors species that existed for a long time, why? • Role of continental drift • Mass extinctions and adaptive radiations

  12. Key Events in Life’s History • Photosynthesis-oxygen revolution-2.7 billion years ago (photosynthetic bacteria) • First eukaryotes-2.1 billion years ago, result of endosymbiosis • Origin of multicellularity-1.5 billion years ago • Cambrian Explosion-535-525 million years ago • first predators, first hard bodied organisms, Cnidaria, Porifera, and Mollusks, bilateral symmetry • Colonization of land-began with cyanobacteria 1 billion years ago, necessary adaptations?

  13. Genesis of Eukaryotes:Serial Endosymbiosis? • Membrane-bound nucleus • Mitochondria, chloroplasts, and the endomembrane system • Cytoskeleton • 9 + 2 flagella • Multiple chromosomes • Mitosis, meiosis, and sex

  14. The Origin of Eukaryotes?

  15. Secondary Endosymbiosis

  16. Continental Drift • Pangea: supercontinent, broke apart during Mesozoic era. • Explains distribution of fossils and extant organisms. (lungfishes, marsupials) • Generated by plate tectonics • Can result in volcanoes (Krakatau, Tambora), tsunamis.

  17. Examples of Mass Extinctions • Approximately 12 mass extinctions • Permian extinctions-250 million years ago, 90% species (marine) eliminated • Cretaceous extinctions-65 million years ago, 50% marine species, dinosaurs, many plants • Asteroid impact (Alvarez or Impact Hypothesis), crater from Cretaceous extinction- 180 km dia. Yucatan coast • Role of the Siberian Traps (caused O2 to drop from 30% to 15% or lower during the Permian period)

  18. Consequences of Mass Extinctions • Widespread adaptive radiations • Causes?

  19. Mass extinctions

  20. DNA, RNA and Protein Comparisons • DNA hybridizations-compare degree of similarity between two species • Restriction maps • DNA sequence analysis • Homologous DNA sequences-mutations accumulate as species diverge • Molecular clocks-number of amino acid substitutions is proportional to the elapsed time since divergence

  21. The Origin of Evolutionary Novelty • How do novel features that define taxonomic groups above the species level arise? (wings as an example) • Gradual refinement of existing adaptations • Alternative functions • Exaptation: structure that evolved in one context and later was adapted for another function. Examples: feathers, light hollow bones in birds

  22. Genes that control development and evolutionary novelty • Sometimes a few changes in the genome causes major changes in the morphology. • A system of regulatory genes coordinates activities of structural genes to guide the rate and pattern of development • Allometric growth • Heterochrony • Paedomorphosis • Homeosis

  23. Heterochrony-alteration in the time of change in the order of one or more events

  24. Allometric Growth-different body parts grow at different rates. Result: adult is shaped different form the juvenile.

  25. Paedomorphosis: type of heterochrony that describes a condition in which the time of sexual maturity is altered. Retention of ancestral juvenile structures in a sexually mature adult organism

  26. Homeosis-alteration in the placement of different body parts

  27. Hox genes • Homeotic genes • Responsible for where structures develop on the embryo • Responsible for limb formation instead of fin formation

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