Any method can be chosen based on what the sample is, how recent it is, and how big it is (ie how much you can destroy to get an answer).I presume you mean that isotopic dating is applicable to rocks?

One indication for the age of the Egyptian pyramids is their alignment to a calculated geologic reference that changed with time due to the precession of the Earth.A huge amount of work is currently underway to extend and improve the calibration curve.