FOSSILS & RELATIVE DATING by ME55CW

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									   FOSSILS &
RELATIVE DATING
ROCKS TELL A STORY

 Rocks can tell where they
  were made and when

 Sedimentary rocks can
  have fossils in them

 Rocks can tell when mass
  extinctions happened
PALEONTOLOGY
the study of fossils  remains of ancient life
   Body fossils vs. trace fossils
       Body = remain of organism, like bones;
       Trace = evidence of organism, like footprints

   Scientific dating
       Absolute dating (gives age in years)
        Radiometric / radioactive dating (isotopes)
       Relative dating (gives age before, after, during) Observation of
        rock layers
    FOSSILS
    Traces and preserved remains of ancient life
     found within rock layers
   Fossils show:
       Biodiversity
       How species have changed over time
       Correlation between rock layers from around the world
       Relative ages to particular strata
       Evidence for the geological time scale
RELATIVE DATING & AGE
 Relative Dating: putting
  rocks and geological
  events in correct
  chronological order

 Relative Age: how old
  something is in
  comparison to something
  else

 HOW?
    Use of sedimentary rocks
    Use of fossils
    Study of strata
  INDEX FOSSIL
   Fossil that defines and identifies geologic
   periods; often in only one layer of rock

 Easily recognizable

 Short-lived (found only in a few layers of rock
  worldwide)

 Wide distribution (geographic range)
Ex/ INDEX FOSSIL: AMMONITE
    Ammonite fossils are
     found worldwide, but
     they existed for only a
     very specific period of
     time

    this means ammonites
     are found in very
     specific layers of rock

    when an index fossil is
     found, the age of the
     rocks it is preserved
     can be determined
Two Conceptions of Earth History:
Catastrophism
 Assumption: Great Effects Require Great
  Causes
 Earth History Dominated by Violent Events
Uniformitarianism
 Assumption: We Can Use Cause And Effect to
  Determine Causes of Past Events
 Finding: Earth History Dominated by Small-
  scale Events Typical of the Present.
 Catastrophes Do Happen But Are Uncommon
       Uniformitarianism

Continuity of Cause and Effect
 Apply Cause and Effect to Future -
  Prediction
 Apply Cause and Effect to Present -
  Technology
 Apply Cause and Effect to Past –
  Uniformitarianism
The Present is the Key to the Past
Ripple Marks, Bay Beach
Fossil Ripple Marks, Baraboo Range
Modern Mud Cracks
Fossil Mud Cracks, Virginia
 LAW OF HORIZONTALITY
Sediments are originally deposited in horizontal
  layers



                         Folds or inclines:
                          layers must have
                          been deformed after
                          they were deposited.
LAW OF SUPERPOSITION
For undisturbed rocks, the oldest layer is on
the bottom and the youngest is on top (Supai
is oldest)
    Principle of Crosscutting
 geologic feature which cuts another is the
  younger of the two features.
What kind of rocks
are these fossils in?


Which layer is
oldest?


Which layer is
youngest?


How do you know?
LAW OF SUCCESSION
 Fossils are found in a predictable sequence
 Fossils in rock B are older then fossils in rock A
  LAW OF INCLUSIONS
If a rock body (Rock B)
   contained fragments
   of another rock body
   (Rock A),
then Rock B must be
   younger than the
   fragments of rock it
   contained
     GEOLOGIC TIME SCALE
     a series of time
       intervals that
       divides Earth’s
       history
•   Each layer of rock
    represents specific interval
    of time
•   Index fossils help
    determine specific period
•   Time periods divided by
    specific events like mass
    extinctions
       Pseudofossils

Look Like Fossils But Aren't
 Dendrites
 Concretions
Pseudofossils
Natural or Sculpture?

								
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