Luckily, we can measure these fluctuations in samples that are dated by other methods.
Tree rings can be counted and their radiocarbon content measured.
Radioactive decay can be used as a “clock” because it is unaffected by physical (e.g. For instance, the amount varies according to how many cosmic rays reach Earth.
This is affected by solar activity and the earth’s magnetic field.
Some of the first radiocarbon dates produced showed that the Scottish tombs were thousands of years older than those in Greece.