Can one tell from layers how long an oyster lived?

09 December 2007

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Question

Fossil oyster shells wash up on the beach of the James River, a part of the Chesapeake Bay, in Virginia. They are made of many layers shown of mother-of-pearl. Can one tell from these layers how long such an oyster lived? I've counted up to 52 layers from one of these.

Answer

You probably can date shellfish in this way, and that would suggest that this shell was 52 years old. Like many things in nature, shellfish have annual seasons of rapid growth, and during this far more shell is laid down. This way, you can probably count shell layers just as you would count tree rings.

Comments

I am not sure how old this thread is but oysters generally max out at 20 years. You are able to age an oyster by looking at the growth lines, one dark and one light band is equal to one year. If you are asking about how long ago that oyster lived you could radiocarbon date it but C14 dating on shell is not the most reliable.

Hi,

Is it possible to estimate how long a shell have been on the beach. I work with oysters (art) and I'm so intrigued. I use flat pieces of oyster shell which are peach or grey in colour and I assume they are pretty old! I'd love to know.

Dating things in their context i.e. an artefact in a specific layer is much easier, because you can corroborate and compare a range of dating measures on a range of items in the same context. An item on a beach could have come from anywhere and arrived at any time.

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