The shell of a clam does more than provide a home for mollusks. Clam shells tell about climate changes, seawater salinity and the age of a clam. With the right tools, a layperson can tell the age of a clam by observing the shell it once lived inside.
Know that size doesn’t matter. The oldest known clam was found in 2007 off the coast of Iceland. The 405-year-old clam had a shell less than 6 inches wide.
Open the clam. Unfortunately, this will kill a live clam. The rings on the outside of the clam are not accurate indicators of age. Internal growth patterns are more accurate.
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Use a rock-cutting saw to cut the shell, allowing you to view a cross section of the clam shell. You may need a microscope to get an accurate view.
Look for a pattern of one large white band alternating with a thinner dark band. Each occurrence of a white band with a dark band indicates one annual cycle. The darker band was once the outside of the shell.
Count the pattern. Every white band alternating with a dark band indicates one calendar year. The total number of times this pattern appears in the cross section of your clam shell is the age of the clam in years.