Mollusks and freshwater mosses commonly incorporate carbon dissolved in water, rather than the atmosphere, and the isotopic ratio of old.Corrections can be made for “old carbon” effects on marine shells, although these introduce additional uncertainties in calculated ages. There are two sources of uncertainty in radiocarbon ages.
Similar errors result from modern argon being absorbed on to the surface and interior of the sample, thereby invalidating the second assumption.
Fortunately, atmospheric argon contamination can be assessed by measurement of the different isotopes of argon present.
As such, there is no certainty that the organism was killed by the landslide, which is the conceptual assumption many researchers make when interpreting radiocarbon ages on such fossils.
More correctly, the derived ages should be considered “maxima” for the time of the event.
Similarly, certain rocks may have incorporated older “argon-rich” material during formation.
Such factors result in the sample age being overestimated ().
In ultraclean laboratories, analytical uncertainty can be as low as ±10 years (1 sigma), but in most laboratories, it is of the order of ±50 years (1 sigma).
Second, radiocarbon years are not the same as sidereal (calendar) years; thus, radiocarbon ages must be “calibrated” to bring them into a standard time frame.
Care is also required in interpreting radiocarbon ages.