This is a partially developed activity description. It is included in the collection because it contains ideas useful for teaching even though it is incomplete.
Calibrating Radiocarbon Ages
Topic: Calibrating radiocarbon ages using examples from lacustrine sediments
Course Type: Upper-level undergraduate to graduate students
Access the Neotoma database. Click explorer. Under site name type Moon Lake. Click search. Two sites will show up and find the Moon Lake site in North Dakota which is a kettle lake. Click on the site. Click on the geochronologic dataset. This brings up the spreadsheet of radiocarbon ages. Copy these data into Excel.
Open CALIB. Execute program. Click on calibration and plot options menu. Select 2-sigma, BP, and calibration curve. Click on data input menu. Enter values for Radiocarbon age BP, Standard Deviation in age, Optional (lab code), and Unique (depth). Blank out the sample description line. Click the enter data box to enter the data into the calibration window. Note that the enter data box will not stay checked. Repeat for each date. Click on the Calibrate button and the calibrated ages will appear in the upper panel. Click on spreadsheet export file, this will create a *.csv file that you can open in Excel. An important column is the med._prob. which shows the median probability in calibrated years. Plot on a single graph in Excel the radiocarbon ages and calibrated ages versus sediment depth. Analyze the differences between radiocarbon ages and calibrated ages. Are there time frames where the two data sets are congruent and/or divergent? What processes might be responsible for the congruence and/or divergence in the two data sets of ages?
Further analysis of the graphed data and potential discussion topics:
- Why calibrate radiocarbon ages?
- Calculate varying rates of sediment deposition?
- How might changes in sediment deposition be related to climatic changes?
- How could one use a basal date from a kettle lake to infer timing of glacial recession?
GoalsStudents should be able to do the following:
- Understand the difference between radiocarbon ages and calibrated ages, and the basic processes responsible for this difference.
Students would be assessed on their successful excel plot of data with radiocarbon ages and calibrated ages versus sediment depth