(5 pts)
2. How many atoms are expected to decay before the half-life is over?
3. Why is the number not always perfect?
4. What is the big difference in the decay of uranium compared to carbon?
Choose “custom� and move the “half-life� bar on the chart and choose a decay time frame.
5. No matter time frame what you chose, what is always true of half-life?
Decay Rates Tab
Click on the bar on the bucket and drag it to the right to add atoms. Add several different amounts and watch where the half-life on the graph is (where the red and blue lines cross)
6. Does the amount of atoms that an object has at the beginning matter?
7. What do we call the time where the number of original atoms and the decayed atoms are equal in number?
Measurement Tab
Click on “plant tree� and push the pause button after the 3rd half –life.
8. What happens to the amount of C-14 when the tree dies?
9. If you found a piece of preserved wood, and 65% of the atoms were C-14, how old is it?
Click on “rock�.
10. Why is the C-14 line not forming on the graph?
Click on “uranium-238�, “volcano� and “cool rock�. Notice the change on the time scale.
11. Why is a line forming on the graph now?
Dating Game Tab
To estimate the age of the items found in the layers of sedimentary rock, point the microphone at it and notice the number in the black box. Move the arrow on the graph to that number. (Look in the smaller yellow box above the arrow) Use the graph to estimate the age.
12. If “0.0%� comes up in the black box, what does that mean?
13. Practice estimating the age of several items. Average the age of the items in a layer to find the age of that layer. Fill in the chart below for each sedimentary layer:
Color of Layer
Things in the Layer
Approximate age of the layer.
Dark gray
Bone, cup, skull
blue
Skull, fish skeleton
pink
Fish, sea shell, alligator skull
Yellow green
Sea shells
Light gray
Sea shells
(+5)
EXTRA CREDIT The custom setting indicates that there are other radioactive atoms that can be used to date living things and rocks. If you are really good at this, you can figure out the custom setting. How old is the trilobyte?
All items +1 each
Tables +5 each
total points possible 20
2. The number of atoms expected to decay before the half-life is over depends on the initial number of atoms present. It can be calculated by dividing the initial number of atoms by 2 raised to the power of the number of half-lives.
3. The number is not always perfect because radioactive decay is a random process. While the half-life provides an average time for decay to occur, individual atoms may decay sooner or later than expected.
4. The big difference in the decay of uranium compared to carbon is the half-life. Uranium-238 has a much longer half-life (4.5 billion years) compared to carbon-14 (5,730 years).
5. No matter the time frame chosen, half-life remains constant. Each half-life reduces the number of radioactive atoms by half.
6. The amount of atoms that an object has at the beginning does matter. The more atoms there are initially, the more decay events will occur, resulting in a shorter half-life.
7. The time where the number of original atoms and decayed atoms are equal is called the half-life.
8. When a tree dies, the amount of C-14 remains constant as it no longer takes in carbon from the atmosphere.
9. If 65% of the atoms in preserved wood are C-14, it is approximately 3 half-lives old. Using the 5,730-year half-life of C-14, the approximate age of the wood would be around 17,190 years.
10. The C-14 line is not forming on the graph because the graph is only showing the decay of uranium-238 and not the decay of carbon-14.
11. A line is forming on the graph now because uranium-238 is undergoing radioactive decay and producing daughter isotopes that can be measured.
12. If "0.0%" comes up in the black box, it means that no radioactive isotopes are present in the sample.
13. - (Not enough information provided to fill in the chart)
Extra Credit: To figure out the age of the trilobyte using the custom setting, the specific details of the custom setting are needed.