Dating
Differences
Defined
Absolute vs. Relative Dating
Relative Dating
• A method of determining the age of a fossil by
comparing its placement with that of fossils in
other layers of rock
Absolute Dating
• Any method of measuring the age of an event or
object in years
Activity – Model
• List 5 important events in your life (the
one at the bottom should be the oldest!!
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Started working at Wendell Middle December 2014
Started working at Southwest Middle August 2013
Graduated from Southeastern University May 2013
Started work at Lakeland High School January 2013
Graduated from high school June 2008
Got Braces September 2004
Born November 1990
Radioactive dating
Measurement of the amount of radioactive material
(usually carbon 14) that an object contains; a form of
absolute dating
Uranium
A white,
radioactive
metallic chemical
element that
weighs more than
any other element
in nature; used in
radioactive dating
BrainPop
• See how radioactive dating works by watching
this brainpop: Carbon Dating
Rock Layers
8th Grade Science
Spring 2015
Rock Layer
• The four rock columns were found at the places
indicated by letters A, B, C, D. Different rock
layers are found on the surface at these
places. The problem is to find which layers
match.
• Color the matching sections from A, B, C, and D
the same color.
• Cut out the columns of rock layers.
• Arrange the columns of rock layers side by side
by matching layers.
Do not write what is in purple or teal
• Write the following notes on the
BACK of your Rock Layers Activity
• Title: The Law of Superposition
The Law of
Superposition
8th grade science
Spring 2015
Law of Superposition
States that the oldest rocks lie on the bottom and
the youngest rocks are on top of any undisturbed
sequence of sedimentary rocks.
Correlation
Matching rock
layers in different
locations to see if
they formed at the
same time and
under the same
conditions
Unconformity
• A gap in the rock record
• What could cause an unconformity?
▫ Erosion could cause rock to be worn away and
“disappear”
▫ When plates move together (convergent
boundary) one plate “disappears”
Rock
Layers
Analysis
Questions
• Flip back over to the Rock Layers side and
answer the following questions on that side.
▫ 1. Which rock layer is the oldest? The youngest?
▫ 2. Which fossil is the oldest? The youngest?
▫ 3. What happened to the
layer in rock strip C?
(Where did it go?) Use your vocabulary words to
describe what happened to layer
in rock
strip C.
Sedimentary Rock
• Most fossils are found in Sedimentary Rock
▫ Rock that forms when sediments are compacted
and cemented together
Index Fossil
• A fossil of an organism that is known
to have lived in a particular geologic
age that can be used to date the rock
layer in which it is found
▫ A key example of an organism used as
an index fossil are TRILOBITES, a
group of hard-shelled animals whose
body had three sections, lived in
shallow seas, and became extinct about
245 million years ago
Other Clues to Relative Age
Clues From Igneous Rock
• Lava that cools at the surface is called an
extrusion
• Rock below an extrusion is always older.
Extrusion
Intrusion
• Magma that cools
beneath the surface
is called an
intrusion
• An intrusion is
always younger
than the rock layers
around and
beneath it
The Cross-Cutting Law
• Faults (a break in the
rock) are always
younger than the rock
it cuts through!
• Fractures (a crack in
• The arrow points to a
the rock) are always
fault – notice the
younger than the rock
layer of white rocks
it cuts through
do not line up with
each other
To Summarize
• Generally, the top layer is the youngest – bottom
layer is the oldest
• The rocks below an extrusion (lava at the top)
are always older than the extrusion
• The intrusion (lava within the rocks) is always
younger than the rocks around it
• A fault is younger than the rocks around it
Using your knowledge of the Law of Superposition, put the
following layers in order from the youngest to the oldest.
YOUNGEST
OLDEST
E
_______
D
_______
_______
A
_______
B
_______
C
Practice
• You have two other examples on your worksheet
– try to put the rock layers in order from
youngest to oldest
Items to STUDY for Tomorrow’s Quiz
• Examples of Mechanical and Chemical Weathering
• Vocabulary Definitions:
▫ Relative Dating, Absolute Dating, Radioactive Dating,
Uranium, Correlation, Unconformity, Sedimentary Rock,
Index Fossil
• Law of Superposition
▫ Where are the oldest/youngest rock layers?
▫ What are intrusions, extrusions, faults and fractures?