To learn how scientists determine the age of living and non-living trees. 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. Tree ring The Methuselah Tree has lived more than 4, 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 The bristlecone pine chronology done in the southwest United States stretches back more than 8, years; the European oak and pine chronology goes back more than 11, 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.
Books Schweingruber, Fritz H. Basics and Applications of Dendrochronology. Covers all topics related to dendrochronology. An Introduction to Tree Ring Dating. The University of Chicago Press, Republished by The University of Arizona Press, Provides basic dendrochronology information.