chronometrically

Instead of being based on stratigraphy, these dates are defined chronometrically.

The period is defined chronometrically and is not referenced to a specific level in a rock section on Earth.

The base of the Mesoproterozoic is defined chronometrically, in terms of years, rather than by the appearance or disappearance of some organism.

Instead of being based on stratigraphy as all other geological ages are, the beginning of the Archean eon is defined chronometrically.

Chronometrically Invariant Variations In The Einstein Theory Of Gravitation .