17-1 The Fossil Record by wpDUXY2b

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									   Chapter 17
The History of Life
     Section 17-1
   The Fossil Record
            Current Estimate of
           the Age of the Earth
Scientific methods of estimating the age of the
earth are based on analysis of evidence found in rocks
and on radiometric dating .

Based on these methods, scientists have concluded that
the earth is much more than 6,000 years old.

Recent estimates of the age of the earth:

       4.6 billion years old
                                  (4.6 billion = 4,600,000,000)
    Geologic Time Scale
Developed By Paleontologists To
  Classify Geologic And Biologic
              Events


         Rock Layers
        Fossils Present
Life On Earth
           Fossils & Ancient Life
   Scientists Who Study
    Fossils?
    • Paleontologists
    • Infer What Past Life
         Looked Like
         What They Ate & What Ate
          Them
         Behavior
         Environment They Lived
          In
What They Looked Like
What They Ate
    Fossils & Ancient Life
Key Concept
 The Fossil Record Provides
  Evidence About The History
  Of Life On Earth. It Also
  Shows How Different
  Groups of Organisms Have
  Changed Over Time.
 Fossils can be used to
    1. Show the course of natural
 selection… how organisms change
             overtime.
2. Show changing environments and
             patterns.
Fossil: from the Latin word meaning
             “dug up.”

                             Any organism can
                               leave a fossil.

                               In order to leave a
                                 fossil, organic
                                material changes
             0.1% of organic    from it original
            remains fossilize.    material into
                                   a mineral.
     Bones and shells
         fossil best,
but all things can fossilize.
Conversion: Bone to Rock

            Conversion is a VERY SLOW
          Process. It can take millions of year
                        to occur.

           Dirt builds up over a burial. The
            Pressure from the dirt builds up
          and drives water out of the bone and
             dirt and turns it into ROCK.

           Bone which is made up of calcium
         Converts into rock. The most common
         are calcite aragonite, quartz and silica.
Burial
     Burial is important for
          fossilization.

     Burial protects a bone.

     If a bone is not buried,
     scavengers may eat the
    remains, or the bone will
              decay.

   Without burial, a bone can
    decay in 10 years or less.
                       Discovery
At the same time as fossilization is occurring, other geological
 processes such as mountain formation may raise the fossil
to the surface, where weathering and erosion may eventually
                       expose a fossil.
       How Fossils Are Formed
   Most Form In Sedimentary Rock
   Plants & Animals Die In A Water
    Environment And Are Covered
    With Silt
   Others Covered With Fine Sand
    or Volcanic Ash
   Compressed Into Rock
  4 TYPES OF FOSSILS
 MOLDS:
are fossils
    which
formed from
      an
 impression
of the shape
 or tracks of
      an
  organism.
 4 TYPES OF FOSSILS
     CASTS:
are fossils which
 are formed when
  sediments fill in
 the cavity left by
   decomposing
    organisms.
      4 TYPES OF FOSSILS
   Trace fossils are
    non-body
    remains
    indicating the
    activity
    (behavior) of an
    organism.
4 TYPES OF FOSSILS
TRUE FORM
 FOSSILS:
are fossils of
   the actual
   animal or
  plant. Many
  are trapped
 in ice, amber
     or tar.
   Eggs, Embryos, and
    Nests- Fossilized dinosaur
    eggs were first found in
    France in 1869. Many
    fossilized dinosaur eggs
    have been found, at over
    200 sites. Sometimes they
    have preserved parts of
    embryos, which can help
    to match an egg with a
    species of dinosaur. The
    embryo also sheds light on
    dinosaur development. The
    nests and clutches of eggs
    tells much about dinosaurs'
    nurturing behavior.
      6 ways that organisms
       can turn into fossils
1.  Unaltered
    preservation
 -like insects or plant
    parts trapped in
    amber, a hardened
    form of tree sap
         Unaltered Remains
                            Insects in
                             amber




Preservation in tar
      6 ways that organisms
       can turn into fossils
2. permineralization=petrification
 -in which rock-like minerals seep in
 slowly and replace the original
 organic tissues with silica, calcite or
 pyrite, forming a rock-like fossil -
 can preserve hard and soft parts -
 most bone and wood fossils are
 permineralized
     6 ways that organisms
      can turn into fossils
3. replacement
-An organism's hard parts dissolve and
  are replaced by other minerals, like
  calcite, silica, pyrite, or iron
   This brachipod has
    been pyritized
    (hard structures
    replaced by pyrite
    [fool's gold]).
      6 ways that organisms
       can turn into fossils
4. recrystalization
-hard parts either revert to more
  stable minerals or small crystals turn
  into larger crystals
   These brachiopods lived
    about 375 million years
    ago. The original
    organisms decayed,
    leaving voids in the
    surrounding sediment,
    which were then filled by
    other minerals. In the
    lithified rock, the void
    spaces are represented as
    molds (on the right), and
    the sedimentary fill is
    represented by casts (on
    the left).
     6 ways that organisms
      can turn into fossils

6. carbonization=coalification
 (When the organism dies most of the
 elements in its body -- such
 as hydrogen, oxygen, and nitrogen -
 - are removed, but the carbon, which
 appears not only in living bodies but
 also in diamonds, coal and many
 other mineral items, remains.)
These are
carbonized
fronds of
Mariopteris,
an inhabitant
of Late
Carboniferous
swamps.
Most animals did not fossilize
they simply decayed and were lost
 from the fossil record.
 Paleontologists estimate that only a
 small percentage of the dinosaur
 genera that ever lived have been or
 will be found as fossils.
           Fossils & Ancient Life
   Each Fossil Is Found Only In It’s
    Particular Time Period or Layer
   A Kind Of Fossil Clock
   Of All The Life Forms That Have
    Ever Lived On Earth -----
    • 99% Are Extinct
         No Longer Alive
        Fossils & Ancient Life
   Fossil Record
    • Organization Of
      Fossils From Oldest
      To Newest
      Including
      Supporting
      Information Of
      Other Life Forms In
      Their Environment
         Interpreting Fossil Evidence

   Fossils Are
    Released By
    • Tectonic
      Forces
    • Erosion
    • Mining
    • Construction
       Interpreting Fossil Evidence

   Most Fossils Disarticulated
    • Predation
    • Scavengers
    • Rot
   Catastrophic Events May Bury
    & Preserve Whole Animals
    and/or Ecosystems
              Dating Fossils
       Two Types of Dating
1.   Relative Dating
      Organizes Fossils By Order (1st, 2nd, 3rd,
        etc.)
      Tells You Which Organisms Lived In
        What Order
      Does Not Give You Actual Years
2.   Absolute Dating
      Gives You Age In Years Before Present
      e.g. 150 Million Years Ago
                  Relative Dating
        Using the
  Law of Superposition
(successive layers of rock
were deposited one on top
 the other) scientists can
estimate the “Relative” age
  of a fossil. Fossils are
 approximately the same
 age as the layer they are
         found in.
 The younger fossils are
    found closer to the
 surface, the older fossils
  are found in the deeper
           layers.
Relative Dating
            Relative Dating
   Can determine
    a fossil’s
    relative age
   Performed by
    estimating
    fossil age
    compared with
    that of other
    fossils
   Drawbacks –
    provides no
    info about age
    in years
          INDEX FOSSILS
   GUIDE Fossils
    • Easily Recognized
    • Existed For A Short
      Period
    • Wide Geographic
      Distribution
    • Does Not Give
      Absolute Age
Trilobite
Absolute dating
           Can determine the
            absolute age in
            numbers
           Is performed by
            radioactive dating –
            based on the amount
            of remaining
            radioactive isotopes
            remain
           Drawbacks - part of
            the fossil is destroyed
            during the test
Absolute or Radioactive Dating
Key Concept:
 In Radioactive Dating,
  Scientists Calculate The Age
  Of A Sample Based On The
  Amount Of Remaining
  Radioactive Isotopes It
  Contains
Radioactive Dating Or Absolute
            Dating
 Uses The Half Lives Of Certain
    Radioactive Isotopes To
  Calculate The Age Of A Fossil
          Half Life
The Length Of Time Required
  For Half Of The Radioactive
 Atoms In A Sample To Decay
          Carbon-14 Dating
   By looking at the ratio of carbon-
     12 to carbon-14 in the sample
    and comparing it to the ratio in a
    living organism, it is possible to
    determine the age of a formerly
       living thing fairly precisely.
Carbon-14 Dating
      Carbon-14 Dating
The carbon-14 decays with its
half-life of 5,730 years, while the
 amount of carbon-12 remains
     constant in the sample.
      Carbon-14 Dating
  Because the half-life of
carbon-14 is 5,730 years, it is
   only reliable for dating
 objects up to about 60,000
          years old.
half-life of 1.26 billion years
                  COMPARING RELATIVE DATING AND
                  RADIOACTIVE DATING OF FOSSILS

                    RELATIVE DATING                  RADIOACTIVE OR
                                                     ABSOLUTE DATING


CAN DETERMINE       AGE OF FOSSIL WITH RESPECT TO    AGE OF A FOSSIL IN YEARS
                    ANOTHER ROCK OR FOSSIL (THAT
                    IS, OLDER OR YOUNGER


IS PERFORMED BY     COMPARING DEPTH OF A FOSSIL’S    DETERMINING THE RELATIVE
                    SOURCE STRATUM TO THE            AMOUNTS OF A
                    POSITION OF A REFERENCE FOSSIL   RADIOACTIVE ISOTOPE AND
                    OR ROCK                          NORADIOACTIVE IOSTOPE IN
                                                     A SPECIMEN


DRAWBACKS           IMPRECISION AND LIMITATIONS      DIFFICULT LABORATORY
                    OF AGE DATA                      METHODS
    Other useful radioisotopes for
      radioactive dating include

   Uranium-235 - 704 million years
    (decays to Lead-207)
   Potassium-40 - 1251 million years
    (decays to Argon-40 and Calcium-
    40)
   Uranium-238 - 4468 million years
    (decays to Lead-206 and Helium)
   Rubidium-87 - 48,800 million years
    (decays to Strontium-87)
 That’s
all folks!

								
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