The Dating Game: Radioactive Half-life Carbon Dating

Materials

*100 m&ms in cup *index card *Graph paper (one per student) *Rulers *Paper towel

Procedures:

  1. Obtain above materials
  2. Do not write on this sheet of paper
  3. Create a table to collect data

Half-life of M&M

Trial (years) / Unchanged Candies
(M side up)
1
2
3
4
Etc.
  1. Place index card over m&m in cup turn cup over a couple of times and dump out on paper towel.
  2. Remove all candies that are m side down.
  3. Count and record all unchanged candies (m side up)
  4. Create a graph to display you data.
  5. Answer below questions using complete sentences.

Questions:

  1. What is the half-life of M&Ms?
  2. If 25 M&Ms are left unchanged, how many years have past?
  3. How does this activity represent carbon dating? How do your values compare to the table below?

Radioactive Decay and Half-Life of Carbon 14

Years Since Death / Carbon-14 Atoms Remaining
0 / 10,000
5700 / 5000
11,400 / 2500
17,100 / 1250
22,800 / 625
28,500 / 312
34,200 / 156
39,900 / 78
45,600 / 39
51,300 / 20
57,000 / 10
62,700 / 5
68,400 / 2
  1. How many years is added each time you move down a row?
  2. What happens to the amount of Carbon-14 as you move down?
  3. What is the half-life of Carbon-14? (How many years does it take for half of the Carbon-14 to be gone)

Analyze the following stories and answer the questions on another sheet of paper

Teacher Discovers Death in Wright Valley, Antarctica

On January 27, 1999 Tulley stumbled upon a mummified seal in Wright Valley. Although the seal was intact and appeared in good condition(for a dead seal!) the leathery appearance of the skin made all in the expedition wonder about how this seal came to be so far from the sea. How long had this seal been dead?

Eventually the scientists a Carbon-14 radiometric dating test done on the seal’s body. To their astonishment the test found 4,100 radioactive Carbon-14 atoms were present (per every 100,000,000 Carbon 12 atoms) expected in a recently deceased seal.

How long ago did the seal die?

Murder Above the Arctic Circle

The body of a man wearing the traditional clothes of Saami people was found at the bottom of one of the many peat bogs that remain from the last glacial retreat. Buried in the back of his skull was a stone ax made in the archaic style. The stone ax head was sharpened by chipping and the head was bound to a forked wooden handle by crisscrossed hide strips.

Bog acid has tanned the man’s skin. Although his skin is wrinkled and tightly drawn over hex facial bones, he is still distinguishable and his clothes and internal organs are still intact. The withered condition of the body has convinced the police that the homicide happened at least 10 years ago. From forensic evidence, they concluded that he was murdered in a different place, dragged to the bog and tossed in.

After months of investigation no new evidence or information was turned up. Eventually the police requested a Carbon-14 test done on the victim’s body and clothes. To their astonishment the test found that the man’s body and clothes had only 3,000 Carbon-14 atoms present (per every 100,000,000 Carbon 12 atoms), instead of the 10,000 expected for a recently deceased person. This greatly confused the police who assumed that the murder was a recent event.

How long ago did the man die?