GEOLOGIC TIME: Absolute Age NAME________________________________
Refer to Lab book “Absolute Dating of Rocks and Fossils” (new book pages 214-215 and old book 181-182)


1. An igneous rock contains a zircon mineral with 12.5% U235 and 87.5% of Pb207.

What is the parent isotope? ____________ What is the daughter isotope?_______________

What is the per cent of parent isotope found in the zircon? ___________________

How many half lives elapsed: _______

How many years does it take for one half life for U235?_________________(label)

Calculate the absolute age of the rock. Show your work:
Age________________(label)

2. A fossil tree sample contains 50% C14 and 50% N14.

What is the parent isotope? ____________ What is the daughter isotope?_______________

What is the per cent of parent isotope found in the tree sample? ___________________

How many half lives elapsed: _______

How many years does it take for one half life for U235?_________________

Calculate the absolute age of the rock. Show your work:
Age________________

3. How many half lives have elapsed if there is 75% of daughter isotopes in a rock?_____

4. After four half lives, what percent of parent isotope would be present in a mineral? ____

5. A mining company in Pennsylvania has found a peat layer which has been analyzed for Carbon 14 isotopes. The results show that Carbon 14 is present as 25%, and Nitrogen 14 is 75%.

How many half lives have elapsed since the peat layer was deposited? _________

Calculate the age of the peat layer. Show your work.

Age________________

6. Putting together Relative Age Principles and Absolute Age Calculations:

Layers A, B, D, E, F and G are sedimentary.
H is an igneous intrusion
C is an igneous intrusion (sill intruded between B and D)

The wavy dark lines are unconformities (erosion followed by new deposition of sediment)

A. Intrusion H contains a mineral with 25% U235 and 75% Pb 207. Calculate the age of H. Show work and label.

______________________________________


B. Circle the letters of rock units that are older than H: A B C D E F G

C. Circle the letters of rock units that are older than C: A B D E F G H


C. What types of unconformities exist at U_________________________and at V________________________?

D. Put the layers and events in order from oldest to youngest by writing the letters on the lines:


_____ _____ _____ _____ _____ _____ _____ _____ _____ ______
oldest youngest