The average atomic mass for the element is actually 12.011.
Since you never really know which carbon atom you are using in calculations, you should use the average mass of an atom.
Relative dating stems from the idea that something is younger or older relative to something else.
In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
Regional government officials said five adults remained in a serious condition at a hospital in Santander where the British youngsters, many of whom are thought to have been admitted as a precaution because they suffer asthma, spent most of the day.