To learn how scientists determine the age of living and
- 2 copies of the "Tree-Ring Science" student handout
Tell students they will be taking on the role of a dendrochronologist, a tree-ring scientist. Provide each student with two copies of the "Tree-Ring Science" student handout.
Students will be crossdating tree-ring samples to determine which sample is oldest, and will then determine the age of the oldest sample. This works by comparing the patterns in the tree-ring samples obtained from trees in the same region that have experienced similar weather conditions.
Have students cut out the samples and study them carefully for patterns. Make sure students understand how to identify a tree ring.
Have students start with the living tree sample and match any portion of its rings with one of the other samples. Have them continue that process until all the samples are used. Then have them count back from the living sample to the end of the last sample to determine the age of the oldest specimen in the group. (See Activity Answer for an example.)
The technique in this activity is a simplified representation of how dendrochronologists date trees. Inform students that the samples they are looking at represent young trees from the same area with no abnormalities. Usually, dendrochronologists use older trees and many more samples to ensure that the crossdating is correct.
As an extension, have students explore other ways that scientists study core samples to learn about past climates, including soil cores, ice cores, and coral reef cores.
The Methuselah Tree has lived more than 4,600 years. The tree rings on Methuselah and other trees result from the annual growth cycle.
Large cells, made during the spring when rain is abundant, mark the start of a tree ring. As the seasons continue, growth slows and then finally stops until the following spring. A continuum of cell growth size can therefore be seen for each year.
The sizes of each ring depend on many factors, including location, temperature, soil condition, wind, snow accumulation, sunlight, land gradient, and tree physiology. In addition, ring growth is not always annual, so a ring may be absent from a core sample. These are some reasons why scientists can't rely solely on counting rings and must use crossdating from multiple samples to ensure accurate age determination.
The correct tree sample lineage for the activity is:
The age of the oldest tree in the sample is 35.
The bristlecone pine chronology done in the southwest United States stretches back more than 8,500 years; the European oak and pine chronology goes back more than 11,000 years.
Besides dating trees and revealing past climate data, dendrochronology is used to provide information about glacial activity, volcanic events, and even past insect outbreaks. You may want to tell students that scientists rarely cut down the trees they research. Instead, they drill a core sample, about the width of a pencil, through the tree.
Schweingruber, Fritz H.
Tree Rings: Basics and Applications of Dendrochronology.
Dordrecht, The Netherlands: D. Reidel Publishing Co., 1987.
Covers all topics related to dendrochronology.
Stokes, Marvin A. and Terah L. Smiley.
An Introduction to Tree Ring Dating.
Chicago, IL: The University of Chicago Press, 1968. Republished by The University of
Arizona Press, 1996.
Provides basic dendrochronology information.
NOVA Online—Methuselah Tree
On this Web site, look at Methuselah and other bristlecone pines using QuickTime VR, learn how scientists date trees, discover the nature of longevity, and find out how photosynthesis occurs.
The Ancient Bristlecone Pine
Shows how and where these bristlecone pines were found, and tells about their unique strategies for survival.
Crossdating Tree Rings Using Skeleton Plotting
Presents information on how to create
Majestic Trees of America Timeline
Highlights some tree-related milestones from
2000 b.c., around when the oldest living tree was born, to 2001 a.d., the year America voted for a
Ultimate Tree-Ring Web Pages
Provides comprehensive information about
dendrochronology and links to a wide range of
The "Tree-Ring Science" activity
aligns with the following National Science Education Standards:
Science Standard C:
Structure and function in living systems
Cells carry on the many functions needed to
sustain life. They grow and divide, thereby
producing more cells. This requires that they
take in nutrients, which they use to provide
energy for the work that cells do and to make
the materials that a cell or an organism needs.
Science Standard C:
Plant cells contain chloroplasts, the site of photosynthesis. Plants and many microorganisms use solar energy to combine molecules of carbon dioxide and water into complex, energy rich organic compounds and release oxygen to the environment. This process of photosynthesis provided a vital connection between the sun and the energy needs of living systems.