Lab Report

Atomic Dating Using Isotopes

Answer the following questions about the results of this activity. Record your answers in the boxes.

Send your completed lab report to your instructor. Don’t forget to save your lab report to your computer!

Reference: Isotope Half-Life Chart

Isotope / Product / Half Life
Carbon-14 / Nitrogen-14 / 5730 years
Potassium - 40 / Argon - 40 / 1,280 million years
Rubidium - 87 / Strontium -8 7 / 48,800 million years
Thorium - 232 / Lead – 208 / 14,010 million years
Uranium - 235 / Lead - 297 / 704 million years
Uranium - 238 / Lead - 206 / 4,470 million years

Activity 1 – Calibration

Place your data from Activity 1 in the appropriate boxes below. Calculate the age of the calibration standards using the following information.

  • Fraction of sample remaining =remaining ppm of sample/initial ppm of sample
  • Age of sample = half-life value of isotope X number of half-lives elapsed

Calibration Standard / Initial ppm / Remaining ppm / Age of Standard
Low
Carbon-14
High
Uranium-235
  1. Explain if the instrument appears to be calibrated based on the data you obtained for the Low Calibration Standard.

  1. Explain if the instrument appears to be calibrated based on the data you obtained for the High Calibration Standard.

  1. Explain which would be the best isotope from the Isotope Half-Life Chart to measure a 3 billion year old specimen.

Activity 2

Place your data from Activity 1 in the appropriate boxes below. Calculate the age of the calibration standards using the following information.

  • The initial carbon-14 content of the tree specimen is 6% of the carbon-12 content of the specimen.
  • The initial carbon-14 content of the insect specimen is 8% of the carbon-12 content of the specimen.
  • The initial carbon-14 content of the bat specimen is 8% of the carbon-12 content of the specimen.

Formulas:

  • Estimated initial carbon-14 content = % of carbon-12 ppm value (from above) X carbon-12 in specimen/100
  • Fraction of carbon- 14 remaining in sample =remaining ppm of sample/initial ppm of sample
  • Age of sample = half-life value of carbon-14 Xnumber of half-lives elapsed

Sample / Carbon-14 ppm / Carbon-12 ppm / Estimated Initial Carbon-14 / Estimated Age of Specimen
Tree Fossil Specimen
Insect Fossil Specimen
Bat Fossil Specimen
  1. Explain how you obtained the estimated initial value of the carbon-14 content.

  1. Describe if the age of the each specimen is likely a realistic value. You will need to use the web to evaluate the approximate age of the oldest specimen that is possible for trees, insects, and bats.