Transcript Determining the Age of Rocks and Fossils

DO NOW
• Don’t forget on-line fossil activity due
tomorrow.
• Answer these questions in the DO NOW of
your binder:
1. How old is rock if it contains 50% parent
material and 50% daughter material and the
half life is 10 years?
2. What percent of a rock will be parent
material if it is 20 years old and the half life is
10 years?
Procedure Part 2 continued
3 lines:
1. YOUR team’s
data
2. CLASS AVERAGE
data
3. MATHEMATICALLY
PREDICTED data
** Don’t forget a
key!
1.
2.
Procedure Part 3
Fill in the data table for U-235 in Figure 5 for 5 half lives.
The actual half life of U-235 is 704 years, not 2 minutes. Complete
the chart using the actual half-life.
U- 235
parent
start
After
After
1 half life 2 half
lives
128
64
Pb- 207 0
64
Ratio
U: Pb
1:1
Half
lives
1
Years
704 M yrs
daughter
After
_____
half lives
After
After
____ half ____ half
lives
lives
Procedure Part 3
start After After
1 half 2 half
life
lives
1. Go back to the block
diagram (Figure 1) and
figure out how old
U- 235 128
these rocks layers are parent
using the following
information.
2. The ratio of U-235:Pb- Pb0
207
207 atoms in the
daughter
pegmatite is 1:1, and
their ratio in the
Ratio
granite is 3:1. Use what U: Pb
you learned in part 2b
to determine how old
Half
the pegmatite and
granite are. Put those lives
ages in the lines in
Years
Figure 1.
64
64
1:1
1
704
M yrs
After
_____
half
lives
After
____
half
lives
After
____
half
lives
Procedure Part 3 continued
3. Figure 4 is a special
scale called a
logarithmic scale—
different than a regular
graph. You can find the
age of shale/siltstone
layer and the basalt
layer. Shale/siltstone
contains 94% U-235.
How old is it? Fill in the
radiometric age in the
line provided in Figure 1.
4. The ratio of U-2325 in
basalt is 70%. How old is
the basalt layer? Fill in
the radiometric age of
basalt on the diagram in
Figure 1.
ANALYSIS QUESTIONS
1) What is the rock layer that has
acritarchs and bacteria? Based on
the available radiometric ages, can
you determine the possible age of
this rock? Why can't you say
exactly what the age of the rock is?
2) Which rock contains trilobites?
Based on the available radiometric
ages, can you determine the
possible age of this rock? Why
can't you say exactly what the age
of the rock is?
3) What is the age of the rock that
contains the Triceratops fossils?
Why can you be more precise
about the age of this rock than you
could about the ages of the rock
that has the trilobites and the rock
that contains acritarchs and
bacteria?