These assumptions are based on the axioms or worldview the scientist is operating within.This worldview is the basis for an entire system of theories.
Geochronology is the scientific study of the age of the Earth and the temporal sequence of events related to the formation of the planet and the history of life on Earth.
The word is derived from Geo meaning Earth, and chronology, which is the study of time, or a record of events in the order of their occurrence (timeline).
Creation science is one theoretical system and evolution is another.
Thus even when creationists and evolutionists use the same dating methods, they will more often than not achieve radically different results.
The methods are all ultimately calibrated to relative dates of the geologic column, such that data that conflicts with a fossil's or rock's placement in the geologic column is explained away by the evolutionary theoretical system.