Accuracy. Using carbon dating for things that long ago gives you only a rough idea. Counting tree rings is precise, but tree ring chronologies are relative, unless they can be continued to the present or anchored to an event with a known date. These researchers did the latter, using a global and well-dated Miyake event.

The innovation is to find traces of a global cosmic-ray event with which to connect the dating of objects in one local area, Greece, where the dendrochronological data is not continuous, with those in far away local areas, for example England/Ireland, where we have continuous dendrochronological data