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Chapter 25.2 The Fossil Record

Chapter 25.2 The Fossil Record. Dion Kevin, Luke Leary, Crayton Bowie AP Biology 3 rd /4 th. Overview. The Fossil Record Crayton How Rocks and Fossils are Dated Dion The Origin of New Groups of Organisms Luke. The Fossil Record. Provides a window into the past

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Chapter 25.2 The Fossil Record

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  1. Chapter 25.2The Fossil Record Dion Kevin, Luke Leary, Crayton Bowie AP Biology 3rd/4th

  2. Overview • The Fossil Record • Crayton • How Rocks and Fossils are Dated • Dion • The Origin of New Groups of Organisms • Luke

  3. The Fossil Record • Provides a window into the past • Reveals changes and supports evolutionary ideas • Fossils are primarily accumulated from • Sedimentary rocks • Layers are called strata • Insects in amber • Fossilized tree sap • Mammals frozen in ice

  4. The Fossil Record, cont. • The fossil record offers an incomplete chronicle of evolutionary change • The fossil record has gaps because of: • Many didn’t die in the right place @ the right time • Some were destroyed by geologic processes • Only a fraction have been discovered • As a result, only creatures which were abundant and alive for a while bias the fossil record

  5. Fossil Record, cont.

  6. How Rocks and Fossils are Dated • Radiometric Dating- a method for determining the absolute ages of rocks and fossils, based on the half-life of radioactive isotopes. • The rate of decay is expressed as a half life, the time required for 50% of the parent isotope to decay. • Radiocarbon Dating- a specific method using carbon-14 to determine fossil age • All organisms contain carbon, so this is most useful. However, it is only accurate up to 75,000 years • Uranium-238 half-life: 4.5 billion years • Carbon-14 half-life: 5730 years • Potassium-40 half-life: 1.3 billion years

  7. How Rocks and Fossils are Dated, cont. • Magnetism • During the formation of volcanic and sedimentary rocks, iron particles can align themselves with the Earth’s magnetic field. • The magnetic field of Earth has changed multiple times in its history, therefore alignment patterns can be matched with other areas of rock and the age can be determined. • *It is important to note that much of fossil dating is with relation to other rocks*

  8. The Origin of New Groups of Organisms • Fossils provide evidence of the origin of new groups of organisms • Along with amphibians and reptiles, mammals are considered tetrapods, with four limbs. • Mammals with unique anatomical features that fossilize readily have a good fossil record. Mammals Other Tetrapods • Single dentary bone composed of several bones • 3 bones in middle ear single bone (stirrup) (hammer, anvil, stirrup) • Incisors, canines, molars undifferentiated, single- pointed teeth

  9. The Origin of New Groups of Organisms, cont. The fossil record shows that the unique features of mammals evolved in a series of gradual modifications in a group of tetrapods called synapsids. The features of mammals arose gradually in a previously existing group, the cynodonts.

  10. Video http://www.youtube.com/watch?v=c_DCP4cLVNg

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