When an organism dies, it stops taking in new carbon-14, and whatever is inside gradually decays into other elements.
Carbon-14 normally makes up about 1 trillionth (1/1,000,000,000,000) of the earth’s atmosphere.
Most archaeological items can’t be directly carbon dated, so their dating is based on testing done on nearby objects or materials.
If the spear head is dated using animal bones nearby, the accuracy of the results is entirely dependent on the assumed link between the spear head and the animal.
This is perhaps the greatest point of potential error, as assumptions about dating can lead to circular reasoning, or choosing confirming results, rather than accepting a “wrong” date.
Several factors affect radiocarbon test results, not all of which are easy to control objectively.
For this reason, it’s preferable to date objects using multiple methods, rather than relying on one single test.
Second, radiocarbon dating becomes more difficult, and less accurate, as the sample gets older.
The bodies of living things generally have concentrations of the isotope carbon-14, also known as radiocarbon, identical to concentrations in the atmosphere.Even then, a large proportion of radiocarbon dating tests return inconsistent, or even incoherent, results, even for tests done on the same sample.The explanation given for these outliers is usually “contamination.” Inconsistent results are another reason why multiple samples, multiples tests, and various parallel methods are used to date objects.Due to all these factors, it’s common for carbon dating results of a particular sample, or even a group of samples, to be rejected for the sole reason that they don’t align with the “expected” results.That’s not unusual in science, so far as it goes, but the relationship between assumptions and interpretations must be kept in mind. At worst, it can make carbon dating circular and self-confirming, though there are other means of dating that can reduce this risk.Radiocarbon dating can’t tell the difference between wood that was cut and immediately used for the spear, and wood that was cut years before being re-used for that purpose.