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

data2. CLASS AVERAGE

data3. MATHEMATIC-

ALLY PREDICTED data

** Don’t forget a key!

Procedure Part 31. Fill in the data table for U-235 in Figure 5 for 5 half lives.2. The actual half life of U-235 is 704 years, not 2 minutes.

Complete the chart using the actual half-life.

start After1 half life

After2 half lives

After_____ half lives

After____ half lives

After____ half lives

U- 235parent

128 64

Pb- 207daughter

0 64

RatioU: Pb

1:1

Half lives

1

Years 704 M yrs

Procedure Part 3

1. Go back to the block diagram (Figure 1) and figure out how old these rocks layers are using the following information.

2. The ratio of U-235:Pb-207 atoms in the pegmatite is 1:1, and their ratio in the granite is 3:1. Use what you learned in part 2b to determine how old the pegmatite and granite are. Put those ages in the lines in Figure 1.

start After1 half life

After2 half lives

After_____ half lives

After____ half lives

After____ half lives

U- 235parent

128 64

Pb- 207daughter

0 64

RatioU: Pb

1:1

Half lives

1

Years 704 M yrs

Procedure Part 3 continued3. 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 QUESTIONS1) 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?