Shellfish remains are common in coastal and estuarine archaeological sites, but dating these samples require a correction for the “reservoir effect” a process whereby "old carbon" is recycled and incorporated into marine life especially shellfish inflating their actual age in some cases several centuries.

In recognition of this problem archaeologists have developed regional reservoir correction rates based on ocean bottom topography, water temperature, coastline shape and paired samples of terrestrial and marine objects found together in an archaeological feature such as a hearth.

inexpensive dating - Disadvantages of radiometric dating

Limitations and calibration: When Libby was first determining radiocarbon dates, he found that before 1000 BC his dates were earlier than calendar dates.

He had assumed that amounts of Carbon-14 in the atmosphere had remained constant through time.

Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.

So every living thing has a certain amount of radiocarbon within them.

There are two techniques for dating in archaeological sites: relative and absolute dating.

Relative dating stems from the idea that something is younger or older relative to something else.

The Greeks consider the first Olympic Games as the beginning or 776 BC.

The Muslims count the Prophet’s departure from Mecca, or the Hegira, as their beginning at AD 662.

The extra neutrons in Carbon-14’s case make it radioactive (thus the term, radiocarbon).

Radiocarbon is produced in the upper atmosphere after Nitrogen-14 isotopes have been impacted by cosmic radiation.

Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.