How can the age of the earth be measured?
The main method for dating the earth is radiometric dating of old rocks. This measures the relative proportion of elements and their decay products in the same sample of rock.
One of the most useful for dating the age of the earth is uranium-lead dating, which is based on two decay processes:
#""^235"U" -> ""^207"Pb "#with a half life of about #700#million years.
#""^238"U" -> ""^206"Pb "#with a half life of about #4.5#billion years.
This combination of the two processes allows for cross-checking.
It's currently impossible to exactly determine the age of the planet, and even of the universe.
The age of the earth or any other planet cannot be measured, because: did you know that the Radioactive Decay is inconstant?
Additional info: Neither the age of the universe can be determined, because Halton Arp proved that the Doppler Effect is not associated with velocity or distance.