# Uncertainty with carbon 14 dating

Cosmic radiation entering the earth’s atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.

Carbon-14 moves up the food chain as animals eat plants and as predators eat other animals. It takes 5,730 years for half the carbon-14 to change to nitrogen; this is the half-life of carbon-14.

Measurements can be made with a high degree of precision. Aardsma submitted a sample from a reed mat known to be over 5,000 years old.

The measurement, before calibration, came back with an error bar of /- about 60 radiocarbon years. It should be noted that these measurement uncertainties do not increase linearly as one goes back in time.

A common misconception about radiocarbon dating is that it gives a precise date---3577 B. In actual practice radiocarbon dating can only give a range of dates for a given sample---3650 to 3410 B.

In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young (radiocarbon dating with Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes.Thus it is possible in some instances for two samples from a few decades apart to have the same radiocarbon concentration today, and hence the same apparent radiocarbon age.This happens whenever there is a wiggle in the curve at the time the samples died.Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events.