The combination of these two types of geologic ages makes a complete record of earth's geologic history in terms of the order of events and in terms of how many years ago each event occurred.
Numerical age dating techniques, namely different types of terrestrial cosmogenic nuclide dating (TCND), have achieved an impressive progress in both laboratory precision and regional calibration models during the past few decades.
It is now possible to apply precise TCND even to young landforms like Late Holocene moraines, a task seemed hardly achievable just about 15 years ago.
Correlation can involve matching an undated rock with a dated one at another location.
Suppose you find a fossil at one place that cannot be dated using absolute methods.
Even if dating precision has recently considerably increased, moraines should not be clustered into synchronous moraine-groups based on TCND-ages if their morphological position or sedimentology contradicts such classification.