Chapter 15 Outline

Chapter 15 Outline - Chapter 15 Tracing Evolutionary...

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Chapter 15: Tracing Evolutionary History I. Are birds really dinosaurs with feathers? A. Fossil of the earliest known bird- Archaepteryx - found in 1861. B. John Ostrom of Yale University- 1970s- showed evidence that linked skeleton and birds- spurred controversy on both sides C. Many convinced by reptile origins of birds- i.e. crocodile, alligator D. Cladistics strongly supported Ostrom’s ideas E. Now it is widely accepted that birds are from dinosaurs F. How did bird ancestors learn how to fly? 1. Small dinosaurs used feathers to try to gain extra life when they jumped into the air while chasing prey or escaping predators 2. Dinosaurs climbed tree and then glided back to the ground II. 15.1 The fossil record chronicles macroevolution A. Macroevolution, the major changes in history of life, results from cumulative effects of many speciation effects over time and encompasses the origin of evolutionary novelties B. Geologic record- recent earliest C. 3 eons- Phanerozoic, Precambrian (Proterozoic, Archaean) 1. Phanerozoic three eras: Paleozoic, Mesozoic, Cenozoic 2. Each era has their own period; eras divided by mass extinctions D. Timeline 1. Precambrian- prokaryotes and eukaryotes exist 2. Paleozoic (“ancient animal”)- all life was aquatic until later on when plants and animals established on land 3. Mesozoic (“middle animal”)- age of reptiles, dinosaurs, beginning of mammals and angiosperms (flowering plants)- dinosaurs are extinct by the end except for birds 4. Cenozoic- explosive period of mammals, birds, and angiosperms- humans appeared during the Pleistocene epoch III. 15.2 The actual ages of rocks and fossils mark geologic time A. Record of rocks tells relative ages of fossils not actual ages
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B. Radiometric dating - based on measurement of radioactive isotopes 1. Fossils contain isotope of elements that accumulated when the organisms were alive 2. Every living organism carries the same ratio of carbon-12 and carbon-14 as is present in the atmosphere e and stops accumulating once it dies 3. Scientists measures the decay of both isotopes using its half-lives to tell how old the fossil is 4. E.g. carbon-14 to carbon-12 ratio is 1/16 of the atmosphere- age of skull = 22,920 years because carbon-14 has a half life of 5,730 years 5. Carbon only useful for young fossils, older fossils are dated with potassium-40 which has a half-life of 1.3 billion years- measure volcanic rocks, then use that age to infer age of fossil surrounded by rock 6. Error factor- + 10%
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Chapter 15 Outline - Chapter 15 Tracing Evolutionary...

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