# Does carbon-14 decay while a human is still alive?

My teacher taught me that during carbon-14 dating a fresh live sample is obtained, the activity of carbon-14 in the sample is determined, and then the level of activity is compared with that of the dead sample. From this, the number of years the dead sample has spent in the soil (dead) can be obtained.

I am confused by this explanation, could someone elaborate/clarify?

• What are you actually confused about? Have you looked at the Wikipedia entry on Radiocarbon dating? Or on the HyperPhysics page? Commented Dec 30, 2016 at 11:46

While we are alive we continuously exchange carbon with the environment. We eat food containing carbon, metabolise it and exhale carbon dioxide containing carbon. So most of our body tissue maintains the same ${}^{12}$C to ${}^{14}$C ratio as the environment around us.
However when we die we no longer eat, metabolise and exhale so the carbon ratio in our bodies is frozen in. From the moment of death onwards the ratio of ${}^{12}$C to ${}^{14}$C increases with time as the ${}^{14}$C decays.
• @freecharly Carbon-14 is continuously produced by interactions between cosmic rays and the atmosphere --- mostly $\rm ^{14}N + p \to n + {}^{14}C$.