How Do Trees Record Time?
 ES2905 Building a Master Chronology

By matching plots of abnormally wet and dry years with plots from samples with known dates, it is possible to build a tree-ring chronology, or timeline. In order to compile the chronology, you must know the date of at least one tree ring. A chronology is constructed from skeleton plots that are flipped upside down.

The three skeleton plots in the graphic below represent three different samples of wood. A fire scar in the top sample was analyzed to deduce that the marked ring grew in the year 1100. Your task is to match the patterns on the three samples below to determine the ages of the undated samples.

!   Click and drag the samples back and forth to find where the tree ring patterns match one another exactly. When all three plots are matched with overlapping patterns, you can count back from the known date to determine the year that any ring grew.

9. Compile the master chronology on the graph paper at the bottom of your answer sheet.

• Start by labeling the right edge of the graph paper with the known date of 1100.
• Count ten lines to the left and label it 1090.
• Continue marking off ten-year increments to the left on the graph.
• Start on the right again, adding the tall and short lines from the matched tree rings onto the appropriate years of your graph.

Remember that in a skeleton plot, the tallest lines represent the narrowest tree rings (the driest years). From your chronology, can you list the dates of at least 5 years when droughts occurred?

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