Carbon 14 or radiocarbon dating can be used to
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.Gas proportional counters soon replaced the solid-carbon method in all laboratories, with the samples being converted to gases such as carbon dioxide, carbon disulfide, methane, or acetylene.The diminishing levels via decay means that the effective limit for using c14 to estimate time is about 50,000 years. Subsequent work has shown that the half-life of radiocarbon is actually 5730 ± 40 years, a difference of 3% compared to the Libby half-life.However, to avoid confusion all radiocarbon laboratories continue to use the half-life calculated by Libby, sometimes rounding it to 5570 years.This is the clock that permits levels of c14 in organic archaeological, geological, and paleontological samples to be converted into an estimate of time.The measurement of the rate of radioactive decay is known as its half-life, the time it takes for half of a sample to decay.Pre-treatment seeks to remove from the sample any contaminating carbon that could yield an inaccurate date.Acids may be used to eliminate contaminating carbonates.
Some types of samples require more extensive pre-treatment than others, and these methods have evolved over the first 50 years of radiocarbon dating.
The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere.
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).
Libby calculated the half-life of c14 as 5568 ± 30 years.
This means that half of the c14 has decayed by the time an organism has been dead for 5568 years, and half of the remainder has decayed by 11,136 years after death, etc.