As a child I watched tiny fiddler crabs living in conical shells, and many years later I find that people study fossil turritellids. So now I wonder: how old are shells, typically, that you see on beaches? Do they wear out after a year of sand abrasion? 100 years, a million? Is it known?

  • $\begingroup$ Might be able to do carbon-14 dating on the shells to determine the average age of shells on a beach. I do not know if this has ever been done, but it probably has. No clue where to look for this data. $\endgroup$ – user137 Jul 27 '14 at 5:36
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    $\begingroup$ Apparently it's tricky to radiodate seashells that have stayed in the sea. There's exchange with carbonate from the seawater, etc etc. There are a lot of worn out seashells that you can find on beaches. Conceivably you could do some kind of statistical analysis based on the amount of filled versus empty seashells and the age of the filled ones. (If seashells take one critter-lifetime to decay, you should see roughly equal numbers of live and dead shells) Most seashells are only a couple years old, using the dating method below. $\endgroup$ – Resonating Jul 28 '14 at 15:17

Mollusk shells found on typical east coast (US) beaches can range from days old (the animal that made the shell died recently) to thousands of years old. Some shells in our state, North Carolina, have been dated as 40,000 years old. A high number of "seashells" found on east coast beaches are from mollusks that lived in the marsh on the back side of the island. The presence of these shells on ocean beaches provides evidence of island migration - the island has moved landward over the marsh until what was once the marsh is now the ocean shore. Once buried in the sand, the shell is well preserved until erosion uncovers it. Occasionally, fossilized shells are washed up on beaches after having been dislodged from offshore limestone deposits - these shells can be millions of years old.

-Richard - Carolina Ocean Studies


Ages of shell as a piece can be checked or counted.


1) Examine the shell's ridges with a magnifying glass.

2) Tabulate the number of ridges. You can approximate by number of cell per unit length.

3) Divide the total number of ridges by 365. Each day the little mollusk earns a new ridge, thus total will give you its age.

But, that is age of one shell. If you are asking the age of all of them in a beach, my guess would be as old as the beach.

Read more : http://www.ehow.com/how_6331956_tell-age-seashell.html

  • $\begingroup$ that is interesting but I wonder about the shell, not the animal. If the animal lived ten centuries ago, is it possible that the shell still exists? I call that shell 1000 years old. $\endgroup$ – Bob Terrell Jul 27 '14 at 13:52
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    $\begingroup$ @BobTerrell: Then surely the shell would be as old as the beach. Moreover, carbon dating would the last resort. $\endgroup$ – Devashish Das Aug 1 '14 at 10:51
  • $\begingroup$ The shells you find on the beach are from molluscs (mostly bivalves and gastropods) not insects, which are arthropods. $\endgroup$ – Michael S Taylor Aug 20 '14 at 11:02

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