Chapter 17 :

1. Chapter 17: The History of Life

2. 17-1 The Fossil Record • What is a fossil? • Paleontologist: scientist who studies fossils • Fossil record: provides info about the past… • Incomplete!

3. How do fossils form? • Some trace of an organism must be preserved • Sedimentary rock • Several ways: • Imprint of soft parts • Replace bone/wood/shell with minerals • “perfect preservation” • **not all living things leave fossils!**

4. Interpreting Fossil Evidence • Must find them first- earth erodes • Use pieces- rarely see whole organisms • Look for similarities/differences between fossils and current organisms • Date the fossil

5. Dating Fossils • 1. relative dating- vertical order (oldest at bottom) • Index fossil: distinct fossil used to compare relative ages of fossils • 2. radioactive dating- uses half life of radioactive element to determine age • Half life: length of time required for ½ radioactive atoms to decay • Ex: carbon- 14 (decays) and carbon 12 (no decay)

6. Geologic Time Scale • Represents evolutionary time • Worldwide studies • Use relative dating to organize • Use radioactive dating to get specific date

7. 17-2 Earth’s Early History • How did life begin? (loaded question) • Current scientific view: • Young earth struck by an object (another planet?) • Heat melted the earth- all elements rearranged • Settled by density (core, crust, atmosphere)

8. Water! • 3.8 billion years ago: Earth cooled enough for water • Oceans formed- red from iron • Life began in the water!

9. How did life form? • Miller and Urey • Simulated earth’s early conditions in a lab: • “Primordial soup” • Hydrogen, methane, ammonia gases • Closed off experiment to any “life” • Electric spark (to simulate lightning) • Organic compounds formed! (amino acids) • Simple compounds of primitive earth can create organic compounds

10. Free Oxygen and Life on Earth • bacteria-like organisms were first • Increase in photosynthetic bacteria: • O2 in water = ocean turns blue/green • O2 in air= sky turns blue • O2 kills many life forms • Others learn to adapt or live anaerobically

11. Origin of Eukaryotic Cells • Endosymbiotic theory: idea that eukaryotic organisms formed from a symbiosis among different prokaryotic organisms • Prokaryotes taken up by other prokaryotes • Learn to use O2= mitochondria • Photosynthetic= chloroplast

12. Increasing Diversity Among Organisms • Sexual reproduction: adds genetic variation thru gene shuffling • Multicellularity

13. Geologic Time Line Project • Work in groups of 3 • You will be assigned a time period • You will have 20 min to find the following BASIC info on your period and design a mini poster for it • Period Name • Era in which it belongs • 3-5 defining characteristics • A visual- make it look nice! • Be sure to include your names

14. 17-3 Evolution of Multicellular Life • Precambrian Time (88% of life on earth so far) • Anaerobic to aerobic organisms • Eukaryotes formed • Multicellular organisms • Life in sea only

15. Paleozoic Era • Characterized by diversity of marine life • Cambrian Period: • “explosion” of invertebrate diversity • trilobites (arthropods) • Ordovician and Silurian Periods • Some movement to land • First vertebrate- jawless fish

16. Paleozoic Era (cont.) • Devonian Period • Age of the Fishes (sharks) • First vertebrates on land (amphibians) • Carboniferous and Permian Periods • Reptiles evolve from amphibians • Mass extinction: occurs when many organisms die out at the same time

17. Mesozoic Era • Characterized by dinosaurs and flowering plants • Triassic Period • Age of the reptiles • Dinosaurs • First mammals (small shrews) • Jurassic Period • When dinosaurs ruled the earth… • First bird- Archaeopteryx

18. Mesozoic Era (cont.) • Cretaceous Period • T-Rex ruled • Flying reptiles and birds • Shrubs and flowering plants (fruits) • Mass extinction occurs - no more dinosaurs 

19. Cenozoic Era • Characterized as the age of the mammals • No more competition with dinosaurs • Adapted to land, seaand sky • Tertiary Period: • Insects, grazing animals (grass) • Quaternary Period: • Ice ages, mammoths • Early humans-> Homo sapiens

20. 17-4 Patterns of Evolution • Macroevolution: large scale patterns of processes that happen over a long period of time • Patterns/Trends: • 1. extinction • 2. adaptive radiation • 3. convergent evolution • 4. coevolution • 5. punctuated equilibrium • 6. developmental genes and body plans

21. 1. Extinction • Remember Darwin? Fighting for resources? • Other causes include loss of an entire ecosystem (mass extinctions) • Benefits: opens up habitats for survivors • Usually see a burst of evolution/diversity

22. 2. Adaptive Radiation • Process where a single species or a small group of a species evolves into several different forms that live in different ways • Increases diversity of organisms • Ex: Darwin’s finches!

23. 3. Convergent Evolution • Process by which unrelated organisms independently evolve similarities when adapting to similar environments • Ex: penguin (bird), shark (fish) and dolphin (mammal) all develop streamline bodies and swimming appendages • Analogous structures: structures that look and function the same but have no common evolutionary history

24. 4. Coevolution • Process by which two species evolve in response to changes in each other • Ex: orchid’s spur hold nectar 40 cm down and a hawk moth has a 40 cm long feeding tube

25. 5. Punctuated Equilibrium* • Pattern of evolution in which long, stabile periods are interrupted by brief periods of more rapid change • Darwin said gradualism (slow and steady) • Rapid evolution may be due to: • Genetic drift- small pop. • Founder effect- small pop. • Mass extinction- opens new habitats

27. 6. Developmental Genes and Body Plans • Remember hox genes? • Genes cause changes in physical body plan- natural selection then acts on these changes • Ex: ancient insects= wings on all body segments and modern insects have wings on only 1 or 2 segments