What Is a Phytolith?

Unit 4 Activity 4.3Ginny King Bradybradyg@nscdiscovery.org

Phytolith, n. A microfossil of a plant, created by deposits of a mineral called silica in cell walls. The silica remains after the plant dies, forming a three-dimensional copy of the plant’s cells. Paleobotanists studying such a copy can recognize the kind of plant from which it came. Most phytoliths are 10 to 100 microns long. (A micron is one-millionth of a meter.)

Purpose:

In this activity, you will use STRI scientist Dr. Dolores Piperno’s methods and actual lakebed data to learn about Panama’s past vegetation. You will then compare your results with Dr. Piperno’s data and hypothesize about what you’ve discovered.

Dolores PipernoStaff Scientist and CTPA Director

Dr. Dolores Piperno, Director, Center for Tropical Paleoecology and Archaeology

Using Sediment Cores (Page 123)

Long tubes 5 cm X 10 meters

Sediment in lake bottoms

Study core layers every 10 to 20 cm

Radiocarbon datingLake La Yeguada

Focus Questions:

How have people from different time periods used Panama’s land resources?

What methods do scientists use to examine Panama’s past?

How do humans affect tropical forests?

Research Article (page 111)

Dr. Dolores Piperno, a scientist at the Smithsonian Tropical Research Institute, is learning more about the farmers who began clearing the tropical forests to plant crops as early as 7000 years ago! She is researching what kind of crops they grew and where in tropical America they originated. She does this by searching lake sediments for tiny plant fossils called phytoliths.

The Carbon Cycle

The Marker Key What are the three main kinds of plant

remains used to analyze land use and climate change? Phytoliths Pollen grains Particulate carbon

Phytolith: Magnolia A flowering tree

now found in mountainous areas around Panama.

Phytolith: Chrysobalanaciae A family of trees

now found in deep, lowland forests around Panama.

Phytolith: Trichomanes A fern now found in

deep, lowland forests around Panama.

Phytolith: Podostemaceae A family of aquatic

plants now found in lowland forests around Panama.

Phytolith: Heliconia A flowering herb

that grows in deforested or burned areas

Pollen Grain: Oak (Quercus) A forest tree now

found in mountainous areas around Panama.

Pollen Grain: Secondary Forest Trees

These trees are the first to re-grow after original forest is cut down.

Carbon Particle: Charcoal Tiny piece of

charcoal, indicating that vegetation in the area was burned.

Hands-on Exercise:

Read Master F (page 123) and begin to examine your sample sediment core using the Marker Key.

Separate out and identify all the markers in your sample. In paleobotany, a marker is something that

suggests what kinds of climate and vegetation existed in the past.

Next…

With a partner, record the number of each type of “markers” (seeds, grains, beans, and paper dots) on Master G.

Create a bar graph for your sediment sample.

Discuss with your partner…

What can you say about the land surrounding the lakebed when the sediments were forming?

Write the answer on your graph.

View the graphs on Master H:

What does the Y-axis show? The number of years before the present and

the depth in centimeters at which the sample was taken.

What does the X-axis show? The change in concentrations of each

marker.

During what period were there mostly secondary growth forests? Magnolia and oak were at their peak

between 14,000 and 11,000 years ago; a warmer, wetter climate less suitable for these species began about 11,000 years ago. Secondary growth was greatest 1,500 to 5,000 years ago.

When did particulate carbon first begin to appear in measurable quantities? About 11,000 years ago, when humans

began using fire to clear land.

Why do you think heliconia was also abundant then? Heliconia was abundant 11,000 years ago,

perhaps because it thrived in land deforested by humans.

Cross-check with Graph on Master H

In which time period would you place your sediment sample? Why?

Within your group, create a model sediment core by pouring your sediments in to a 500 mL graduated cylinder in chronological order, with the oldest sediment at the bottom.

Describe your sample as it is layered in the model core.

More Questions…

If you had found starch grains from yams in a sample from 9000 years ago, what might you hypothesize about the area from which that sample came? It would be reasonable to hypothesize

that the area was under cultivation.

Conclusion:

What three types of plant remains do scientists use to study the plant history of an area, and what do they represent? Scientists use phytoliths, pollen grains,

and charcoal dust (particulate carbon). Phytoliths and pollen grains mark past plant life. Particulate carbon marks the presence of burned areas.

What is a sediment core and how is it used? A sediment core is a cross-section of a

lake-, stream-, or ocean-bed that is used to analyze what was present during different time periods.

Summarize what Dr. Piperno’s data tells you about changes in the forest and human activity at Lake La Yeguada over this time period. The forest ecosystem changed from one

characterized by cooler temperatures (today known as mountain forest) to one characterized by warmer temperatures (today known as lowland forest). Humans began to burn forest areas for hunting and gathering about 11,000 years ago. They began to farm about 9,000 to 8,000 years ago. The area was disturbed for thousands of years.

Closure

Reading from Jaguar by Roland Smith (pages 181 – 186) Reflect on images

described in this reading.

Illustrate one of the images.

Post your drawing on a mural.

Multimedia use andJTO Integration

Message Boards Chat Session with

Scientist Earth Systems

Digital Lab Carbon Cycle

Novel Integration (page 127)

Jaguar If a sediment core were taken of the lake bottom in the preserve, what information could it have provided?

Standards and Assessments (page 108)

Novice Apprentice Researcher

Self Assessment (page 126)

How Does Human Activity Influence Global Climate? Identified actions that might increase or

decrease levels of carbon dioxide in the atmosphere.

Identified carbon absorbers and carbon emitters. Yes No Not sure

Teacher Preparation

Pages 131 - 133

Adaptations (page 132)

Elementary If analyzing Dr. Piperno’s data is too challenging,

have students simply count the markers in their samples and help them to graph their own results. Then make a composite graph as a class for the entire core.

High School After completing the exercise, have students

write up a summary of what they think is happening during each 1000-year time period, using Dr. Piperno’s graph.

Key Skills:

Asking questions about how vegetation and climate have changed in an area over thousands of years.

Collecting data on plant remains using a model sediment core.

Analyzing graphical data from a paleobotanist and comparing them to data from a model.

Explaining how plant remains, such as phytoliths, pollen, and particulate carbon, can be used to determine changing vegetation and land use.

Credits:

Exploring the Environment http://www.cotf.edu/ete/modules/carbon/effig10_full.html

Terry Ball's Phytolith Page http://reled2.byu.edu/ASCRIPT/TBall/index2.html

Smithsonian Tropical Research Institute http://www.stri.org/Scientific_Staff/Piperno.html

Sharing…

How could this activity be improved? Comments Questions

Contact Holly

hgarrett@cogeco.ca