# Why is Carbon 14 Dating inaccurate?

May 3, 2016

It depends...

#### Explanation:

At a simple level, carbon-14 dating might be based on an assumption that the rate of production of carbon-14 (due to cosmic rays hitting the upper atmosphere) has been fairly constant. It does vary to some extent. Some of the variation in recent centuries has been caused by burning fossil fuels and by above ground nuclear tests. It is possible to make adjustments for these factors.

Secondly we need to assess the half-life of carbon-14. There seem to be various estimates, around the $5715 - 5730$ year mark. Some calibration is possible, especially using ancient trees such as bristle cone pines. Some calibration has been based on samples of wood from ancient egyptian burial sites.

Thirdly, the actual proportion of carbon-14 to carbon-12 is rather small - on the order of $1.5$ parts per ${10}^{12}$.

Radiocarbon dating is generally useful for dating organic items up to about $50000 - 75000$ years old. Beyond that, or for inorganic materials, other radio isotopes are often used.