Tuesday, November 15th, 2011Bell Ringer:

In your science notebooks, answer the following question:

“How do you think the half life of a radioactive element, like Uranium, helps us date rocks?”

Today’s Learning Goal:• How do we assign numerical ages to rocks, and

ultimately, the earth?

Today’s Agenda:• Introduction to Radioactive Decay• Age Dating Activity

Part of an Atom Mass (amu) Charge

Electron 0 -1

Proton 1 +1

Neutron 1 0

Review the Atom

3 Types of Radioactive Decay

• Alpha Decay

• Beta Decay

• Gamma Decay

http://www.youtube.com/watch?v=o-9yt7OAYmE

Half-Life

The time it takes for half the radioactive atoms to decay to the more stable isotopes

To find the age of a substance:

#half-lives X half-life of the element = AGE

Ex:1.2 half-lives X 704,000,000 years=

844,800,000 years old

Half-Life

Half-Life

Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table 10 Table 11 Table 12 Ave

0

1

2

3

4

5

6

7

8

9

10

Half-Life % Predicted Atoms Remaining

% Parent Isotopes Remaining (14C)

% Daughter Isotopes (14N)

0 100%

1 50%

2 25%

3 12.5%

4 6.25%

Table 2. Number of Parent to Daughter Isotopes

Trilobite

Fish

Reptile

Saber-toothed Tiger

Fossil % Uranium-235

% Lead-207

Trilobite 60% 40%

Fish 75% 25%

Reptile 85% 15%

Saber-toothed Tiger 95% 5%

Dr. Limestone’s Data

Calculate the Age of the Fossils

To find the age of a substance:

#half-lives X half-life of the element = AGE

Exit Card:

No Exit Card Today

Tomorrow’s Learning Goals:• How do we assign numerical ages to rocks,

and ultimately, the earth?• Exploration of Earth’s Past!