Here is one example of an isochron, based on measurements of basaltic meteorites (in this case the resulting date is 4.4 billion years) [Basaltic1981, pg. Skeptics of old-earth geology make great hay of these examples.
For example, creationist writer Henry Morris [Morris2000, pg.
Correlating two separated outcrops means establishing that they share certain characteristics indicative of contemporary formation.
The most useful indication of time equivalence is similar fossil content, provided of course that such remains are present.
ANSWER: Relative dating is used to determine the relative ages of geologic strata, artifacts, historical events, etc.
In a separate article (Radiometric dating), we sketched in some technical detail how these dates are calculated using radiometric dating techniques.
Ice cores showed the age of a military plane buried in the artic as thousands of years old.
Similarly, dendrochronology measures the tree rings in trees and assumes they represent years.
The basis for assuming that like fossils indicate contemporary formation is faunal succession.
However, as previously noted, times of volcanism and metamorphism, which are both critical parts of global processes, cannot be correlated by fossil content.