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Chapter 17

Chapter 17. The History of Life. 17-1 The Fossil Record. Paleontologists- scientists who study fossils Fossil Record- all the information about past life forms. Provides evidence of the history of life on Earth. Shows how different groups of organisms have changed over time.

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Chapter 17

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  1. Chapter 17 The History of Life

  2. 17-1 The Fossil Record • Paleontologists- scientists who study fossils • Fossil Record- all the information about past life forms. • Provides evidence of the history of life on Earth. • Shows how different groups of organisms have changed over time.

  3. What the record shows • Certain fossils appear only in certain rock layers • Some older, some more recent 99% of all species on Earth are extinct

  4. How fossils form • Primarily found in sedimentary rock • Hard parts- bones, wood, shells mineralize • Soft parts- leave impressions • The fossil record is selective and incomplete

  5. Fossil Dating- Relative Dating • Relative dating- the age of a fossil is determined by comparing its placement with that of fossils in other rock layers • Index fossils- used in relative dating. Must be short lived and wide spread

  6. Fossil Dating- Radioactive Dating • Half-life- length of time for half of the radioactive atoms to decay • Radioactive dating- calculating the age based on the amount of radioactive isotopes remaining. • Carbon 14, half-life of 5730 years (useful up to 60,000 years) • Carbon 14 decays into Nitrogen-14 • The ratio of Carbon 12 to Carbon 14 is used Potassium-40 decays into Argon-40, half-life of 1.26 billion years

  7. Geologic Time Scale

  8. 17-2 Earth’s Early History • Earth- 4.6 billion years old • Early Earth atmosphere- hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, sulfide, and water

  9. 4 billion years ago- solid rocks form • 3.8 billion years- water in liquid form, oceans form

  10. First Organic Molecules • 1950s Stanley Miller and Harold Urey • Simulated conditions of the early earth

  11. Stanley Miller and Harold Urey • Hydrogen, methane, ammonia and water combined with an electric spark • Produced amino acids

  12. The Puzzle of Life’s Origin • After the Earth cooled 3.8 billions years ago, 200 to 300 million years later, bacteria form • Proteinoid microspheres- tiny bubbles formed by organic molecules. Selectively permeable membranes

  13. Evolution of RNA and DNA • RNA probably preceded DNA

  14. Free Oxygen • Early Earth’s atmosphere had very little oxygen • 3.5 Billion years ago- bacteria appear • 2.2 Billion years ago- photosynthetic bacteria common • Oxygen combined with iron in oceans • Iron oxide formed and deposited in the oceans

  15. Origin of Eukaryotic Cells • 2 billion years ago- developed of organelles in prokaryotes • Endosymbiotic theory- eukaryotic organisms arose from a mutalistic relationship between prokaryotes

  16. Endosymbiotic theory-evidence • Mitochondria and chloroplasts • 1. contain DNA similar to bacterial DNA • 2. have ribosomes similar to bacteria • 3. reproduce by binary fission

  17. 17-3 Evolution of Multicellular Life • Precambrian • Anaerobic and aerobic bacteria appear • -Eukaryotes appear • Mulitcellular organisms appear

  18. Cambrian • Cambrian Explosion • Shells appear • Invertebrates • Jellyfish • Worms • Sponges Arthropods

  19. Ordovician and Sulurian • Octopi and squid • Jawless vertebrates • Plants on land • Aquatic arthropods

  20. Devonian • Ferns • Insects • Bony skeleton fishes • Vertebrates on land

  21. Carboniferous and Permian • Reptiles • Winged insects • 95% of organisms became extinct

  22. Triassic • Age of Reptiles Fish Insects Reptiles Cone-bearing plants Small mammals

  23. Jurassic • Dinosaurs • Archaeopteryx- first bird

  24. Cretaceous • Dinosaurs • Plants with seeds • 50% of organisms became extinct

  25. Tertiary • Earth warmed • Mammal diversity • Land • Water • Air

  26. Quaternary • Series of ice ages and then warming • Continued diversity of plants and animals • 200,000 modern humans

  27. 17-4 Patterns of Evolution • Extinction • Mass extinction causes • Changing environment: sea levels change, temperature change, land masses move • Accident- asteroid impact

  28. Adaptive Radiation • A single species evolves into many other diverse forms that live in different ways • Example: Darwin’s finches

  29. Convergent Evolution • Process by which unrelated organisms resemble each other • Organisms adapt to a similar environment in similar ways

  30. Coevolution • Process by which two species evolve in response to changes in each other over time • Example- plants and pollinators

  31. Punctuated Equilibrium • Gradualism- slow change over time • Equilibrium- no change • Punctuated Equilibrium- long periods of no change combined with short periods of rapid change • Rapid changes caused by: • Small population • Founders of a new colony • New niches open after mass extinction

  32. Development of Genes and Body Plans • Hox genes- master control genes • Changes in Hox genes have big effects on organisms

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