Jim, Virginia asked:
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.
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.