Studying The Past PowerPoint Notes
Integrated Science 2
I.
Name:
Per:
What is a Fossil?
A. Definition:
II. Why do we Study Fossils Found in Rocks?
A. To provide evidence of
B. To provide information about
C. To provide evidence that populations have
due
to
.
III. Types of Fossils
A. Original Preservation
1.
Description: Plant or animal remains that have not undergone
a.
Uncommon because
,
since death.
or
environments are required to form these fossils.
b.
Examples:
B. Altered Hard Parts
1.
Description: All organic material has been
been
and the hard parts of the organism have
.
a.
Minerals seep in slowly and replace the original organic tissue, forming rock-like fossil.
b.
The fossil has the same
as the original object, but is chemically more like a
.
c.
Examples:
C. Molds and Casts
1.
Description: Fossils that do not contain any
a.
A
or
.
is formed when original shell parts are weathered and eroded, leaving an
of the shell
b.
This cavity might later become filled with
or
.
c.
Examples:
D. Trace Fossils
1.
Description:
evidence of plant and animal life
a.
Provide information about how an organism
b.
Examples:
, moved, or obtained food.
IV. Dating Fossils
A. Relative Age Dating
1.
Definition: Dating rocks and fossils by placing them in chronological order
.
2.
Geologic Principles (used in this dating process)
to create a
a.
Original Horizontality

b.
Sedimentary rocks are deposited in
The Law of Superposition

In an undisturbed sequence, the oldest rocks are
layer is
c.
and each successive
.
Principle of Cross-Cutting Relationships

3.
.
An intrusion or a fault is
than the rock it cuts across.
Other Means of Determining Relative Age
a.
Correlation

Used to date rock layers that are
from each other.

Geologists examine rocks for
(index) and features to help
identify and date them.
B. Absolute Age Dating
1.
Definition: Dating rocks and fossils by using techniques to determine their
2.
Methods:
a.
.
Tree Rings and Seasonal Climatic Changes

Each tree ring represents

Varves are bands of
of growth.
that show a yearly cycle from
.
b.
Radioactive Dating: Dating fossils based on the amount of radioactive material remaining in a
substance over time.

Radioactive substances, (unstable atoms), emit
and
at a
constant rate.

The original element (parent) is

Since the rate of decay is constant, you can measure the
to a different element (daughter).
to determine the age of the rock.

The length of time it takes for
elements
of the original amount to decay is called the
.
Absolute Dating – Applying the Concepts
Example: Uranium-238 will decay into lead-206
What is the Half Life of
Uranium-238?
0 years
100% U
4.5 billion years
50% U, 50% Pb
9 billion years
25% U, 25% Pb
C. A Special Case of Relative/Absolute Dating - Index Fossils
A. Index Fossils
1. Description: Remains of unique species that can be used to
layers or
a particular rock layer
rock
1. Description: Remains of unique species that can be used to
rock layers or
a particular rock layer
a. Must be
,
, and
.
b. Must have lived during a relatively short 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: