The first measurements of radiocarbon were made in screen-walled Geiger counters with the sample prepared for measurement in a solid form.

These so-called "solid-carbon" dates were soon found to yield ages somewhat younger than expected, and there were many other technical problems associated with sample preparation and the operation of the counters.

However, when the organism dies, the amount of c14 declines such that the longer the time since death the lower the levels of c14 in organic tissue.

Plants take up c14 along with other carbon isotopes during photosynthesis in the proportions that occur in the atmosphere; animals acquire c14 by eating the plants (or other animals).

During the lifetime of an organism, the amount of c14 in the tissues remains at an equilibrium since the loss (through radioactive decay) is balanced by the gain (through uptake via photosynthesis or consumption of organically fixed carbon).

Modern AMS (accelerator mass spectroscopy) methods require tiny amounts, about 50 mg.

AMS technology has allowed us to date very small samples (such as seeds) that were previously undatable.

Chemical methods for separating the organic (collagen) from the inorganic (apatite) components of bone created the opportunity to date both components and compare the results.

The collagen fraction usually yields more reliable dates than the apatite fraction (see Dates on bones).Some types of samples require more extensive pre-treatment than others, and these methods have evolved over the first 50 years of radiocarbon dating.For example, it was once standard practice to simply burn whole bones, but the results were eventually seen to be unreliable.In addition to various pre-treatments, the sample must be burned and converted to a form suitable for the counter.The sample must be destroyed in order to measure its c14 content.The carbon-14 it contained at the time of death decays over a long period of time.