Name:______

Dating Dead Stuff: A Lesson in Radioactive Cornium

All organisms have radioactive elements in their body. These radioactive elements are often isotopes of common atoms. Isotopes are useful to scientists because their amounts are stable over the lifetime of the organisms. However, when the organism dies the isotope goes through radioactive decay. This means they break down into a non-radioactive element at a steady rate. This rate, called HALF LIFE, can be measured and offers clues to scientists about how long an organism has been dead.

In this activity, you will determine the half life of a radioactive atom called cornium. When cornium decays, it turns into harmless elements.

Procedure Part A

Step 1: Get baggie A from your teacher. Count the number of radioactive atoms (cornium!). Subtract from 1000 to get the number of stable atoms (beanium!). Record your results of cornium in table 1 on the line “Year 0.”

Step 2: Remove 10cornium atoms. This represents the rate of decay in the first 100 years.

Step 3: Attached is a table with the columns, "years since death" and "no. of cornium atoms remaining." Continue removing 10% of the radioactive cornium for every 100 years until you reach 3000 years. BE CAREFUL! 10% is not the same at 10 atoms! Record your results in the table.

Step 4: Graph the results on a sheet of graph paper, with the year on the x axis and cornium atoms on the Y axis.

Step 6: Get the bags of radioactive cornium representing tissue samples from various dead organisms. Count the number of atoms remaining in each bag and use your table and graph to determine how long ago the organism died. The beanium atoms have been removed because we only need cornium to determine age. Assume each tissue sample began with 100 cornium atoms. Record your results in table 2.

QUESTIONS PART A

1. What is the ratio in year 0 of beanium to cornium? (See step 1) ______

2. You started this activity with 100 atoms of cornium. How many years passed before approximately HALF of the atoms were gone? ______

3. The definition of the term HALF LIFE is the amount of time required for HALF of the atoms of a radioactive substance to be gone. What is the half life of cornium? ______

4. Approximately how many half life periods did cornium go through in 3000 years?

Extra Credit: How many half lives would cornium need to go through in order to completely disappear?

Table 1Table 2

Years since death / Number of cornium atoms remaining / Years since death / Number of cornium atoms remaining
0 / 1600
100 / 1700
200 / 1800
300 / 1900
400 / 2000
500 / 2100
600 / 2200
700 / 2300
800 / 2400
900 / 2500
1000 / 2600
1100 / 2700
1200 / 2800
1300 / 2900
1400 / 3000
1500
Bag with radioactive cornium / Number of cornium atoms / Approximate Age of contents
Bag 1
Bag 2
Bag 3
Bag 4
Bag 5
Bag 6

Procedure Part B: Solve a mystery!

You may have already determined that beanium and cornium are not real atoms. The actual atoms used to date material that was once living is radioactive Carbon, also known as Carbon 14. Scientists use Carbon 14 to determine how long ago something died.

Here is the mystery You are hiking in Northern Minnesota doing some extra credit work for biology, when suddenly you fall into a wetland. This particular wetland is called a bog, and is known to preserve dead things. While you are struggling to get out of the bog, you notice a dead guy floating next to you. You call the authorities, and they are depending on YOU (because of course you are a PC biology student!) to determine how long ago this guy died.

You order a Carbon 14 test to be done, and it is found that for every 1,000,000 stable atoms present in the man's body only 25Carbon-14 atoms were present instead of the 100 atoms expected for a recently dead person.

1. What is the ratio of stable to Carbon 14 atoms in a living (or recently dead) person?

2. How many half lives would the Carbon 14 have to go through to drop to a total of 25 atoms?

3. The half life length for Carbon 14 is 5730 years. Approximately how long had the guy been dead?