Studying The Past PowerPoint Notes
Integrated Science 2
Name:
I.
Date:
Pd:
What is a Fossil?
a. Definition: The evidence or remains of once-living ______________________ or
_____________________.
II. Why do we Study Fossils Found in Rocks?
a. To provide evidence of the past _____________________ of life forms
b. To provide information about past ________________________ conditions
c. To provide evidence that populations have undergone ____________________ due to
____________________ changes (evolution)
III. Types of Fossils
a. Unaltered Remains
1. Description: Plant or animal remains that have not undergone
since death.
a. Uncommon because frozen, extremely dry or ___________________ free environments are
required to form these fossils.
b. Examples (list two):
b. Altered Remains
1. Description: All organic material has been
and the hard parts of the organism have
been
.
a. Minerals seep in slowly and replace the original organic ___________, forming rock-like fossil.
b. The fossil has the same ____________ as the original object, but is chemically more like a
___________
c. Examples:
2. Types of Altered Remains - Molds and Casts
a. An organism dies and gets trapped/buried in ________________________ (sand, ash, etc)
b. The original organism _____________________ or dissolves away leaving a hollow
impression of the organism (______________)
c. This cavity might later become filled with __________________ or sediment to create a
_____________
d. Examples: ____________________________________________
C. Indirect Evidence
1. Description: Trace fossils of plant and animal _______________
a. Provide information about how an organism ________________, moved or obtained food
b. Examples:
IV. Dating Fossils
a. Relative Age Dating
1. Definition: Dating rocks and fossils by placing them in chronological order _____________________
exact dates
2. Geologic Principles (used in this dating process)
a. Original Horizontality
 Sedimentary rocks are deposited in ________________________ layers
b. The Law of Superposition
 In an undisturbed sequence, the oldest rocks are
and each
successive layer is
.
c. Principle of Cross-Cutting Relationships
 An intrusion or a fault is
than the rock it cuts across.
3. Other Means of Determining Relative Age
a. Correlation
 Used to date rock layers that are
from each other.
 Geologists examine rocks for
and features to help
identify and date them.
b. Inclusions
 If a rock contains _________________ of another rock, than the rock that is containing the
fragments must be ______________ than the fragments themselves
c. Unconformities
 _______________ in the geologic record
 May indicate ________________ or deformation of the rock layers
b. Absolute Age Dating
1. Definition: Dating rocks and fossils by using techniques to determine their _________________ age.
2. Radioactive Dating: Dating fossils based on the amount of ___________________ material remaining
in a substance over time.
 When nuclei are _________________ they spontaneously break apart (decay) in a process
called radioactivity.
 The original unstable element (parent) is
to a different stable element
(daughter).
 Since the rate of decay is constant, you can measure the parent to daughter _______________
to determine the age of the rock.
 The length of time it takes for
of the original amount to decay is called
the elements
.
3. Uranium 238
 When rock forms from ______________, it contains U-238 and there is no ___________
present
 U-238 can be used to date rocks formed in the early _________________
4. Carbon 14
 When an organism is alive, it’s C-14 is continuously __________________
 When that organism dies, the C-14 decays to ________________ and it does not get replaced
 C-14 can be used to date geologic evens involving organisms within the past ______________
years
C. A Special Case of Relative/Absolute Dating – Index Fossils
1. Description: Remains of unique species that can be used to __________________ rock layers or to
_________________ a particular rock layer
a. Must be easily recognized, abundant, and widely distributed ______________________.
b. Must have lived during a relatively ______________ time period.
c. If we can date a rock layer ______________________ (exact age), then we can use the
index fossil to date ___________________ rock layers absolutely.
d. If we can only date the rock layer relatively (____________________ age), then we can
use the index fossil to date similar rock layers relatively.
e. Examples: ________________________ were common 245 to 65 million years ago, when
they went extinct