Paleoclimates and Pollen

How do paleobotanists use ancient pollen to find out about the earth's climatic past?

Activity: You will analyze sediment samples with other material mixed in to represent pollen grains and determine the type and amount of the "pollen" in the samples. From this information, you will determine the type of vegetation and age of the samples and will present conclusions about the likely climate at the time the pollen was shed.

Materials

• Samples of sediment containing colored paper dots or shaped confetti to represent pollen
  
  
• Pie pan
  
  
• Tweezers or forceps
  
  
• Key to the different "pollen" colors showing which colors represent which plants, and information about the climatic requirements for each (Washington Table 3 or Colorado Table 4, which your teacher will provide)
  
  
• Worksheet (your teacher will provide)
  
  

Procedure

The following exercise was developed based on actual pollen data collected from a lake in southwest Washington State or a peat bog in the Colorado Rocky Mountains.

1. Your teacher will show a model sediment core containing five (or six) separate layers, each laid down at a different time in the past. Pay attention to the color and texture of each layer to help you identify the samples from the layers you will be working with.
   
   
2. Each pair of students will be given a sediment sample, pie pan, tweezers, a worksheet, and a "pollen" key. Each sample contains "pollen" (actually colored paper dots or confetti, with each color representing pollen from a different species of plant) from plants that grew in the area at the time the sediment was deposited.
   
   
3. You and your partner will separate out the pollen from the sediment. Empty the sediment into the pie pan. Sift and dig until you have found all of the pollen grains. Separate the pollen grains by color or shape.
   
   
4. Use the pollen key to determine what species of plants are represented in your sample and calculate what percentage of the total pollen comes from each species. Fill in the worksheet for the sediment layer you are working on.
   
   
5. Use the pollen key to figure out what the climate was when your layer was deposited. (Use the climate information given with each species description to do this.) Be sure to compare your sediment sample to those in the entire sediment core so that you know what level your sample is from and how old it is.
   

Observations and Questions

1. Compare your conclusions with others in your class who were assigned the same sediment layer. Do you all find the same plant types? Do you all agree on the climate that probably existed at the time?
   
   
2. With your class, discuss the species of plants found in each layer and the climate that probably existed at the time. Fill in the rest of your worksheet with the information provided by other students who studied different sediment layers. Can you determine what the overall pattern of climate change was during these last 20,000 years? Can you speculate about what might have caused the changes?

When you're finished with the activity, click on Back to Teacher Guide at the top of the page.