CHAPTER 6
section 2
Clues About Evolution

I. Clues from Fossils 
    A.  Types of Fossils
          1. most fossils form when remains are buried by sand, clay 
              or mud which eventually turn to rock.
          2. some remains can be frozen for millions of years

          3. some remains can be trapped in tree sap which hardens into amber

     B. Determining a Fossil's Age
          1. Relative Dating
               a. used to tell the age of fossils compared to other fossils
               b. fossils found in lower rock layers are presumed older than
                   fossils found in upper layers
          2. Radiometric Dating
               a. tells a fossil's exact age (absolute dating)
               b. radioactive elements (carbon-14) steadily change into
                    nonradioactive elements (carbon-12)
               c. by determining how much of a radioactive element has
                   changed, scientists can estimate the fossil's age

II. Fossils and Evolution
      A. fossils provide a record of organisms from the past
      B. there are gaps in the fossil record like pages missing from a book
      C. the fossil record shows that simpler life existed first and more
          complex life forms appeared later
      D. the fossil record shows that 99% of all organisms that ever
           existed are now extinct

III. More Clues About Evolution
      A. Direct Observation
            1. antibiotic resistant bacteria
            2. pesticide resistant insects
      B. Embryology
            1. the study of embryos and their development
            2. tails and gill slits are found in embryos of fish, 
               reptiles, birds and mammals
            3. fish keep the gills while others lose them during development
            4. these similarities suggest an evolutionary relationship
                among vertebrates

      C. Homologous Structures
            1. body parts that are similar in origin, but have different functions
            2. ex. porpoise flipper, bat wing & human arm

      D. Vestigial Structures
            1. structures that don't seem to have a function
            2. ex. manatee's and snakes have pelvic bones (hips), 
                but don't have any legs
            3. the human appendix seems to be vestigial
      E. DNA
            1. species with similar DNA suggests they are closely related
            2. some species' DNA is 99.9% the same as another similar species

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