How would you date a sample of rock that you suspect as being one of the earliest on earth?

Radioactive isotope with long half life would be the way to date a sample of rock that you suspect as being one of the earliest on Earth. Archaeologists very often use this method for checking the dates of the materials they excavate. I hope that this is the answer you were looking for and it has come to your help.

Water flows along the east coast and across the western tropical pacific towards south america, while they both are directed towards that way,  el niño does not directly affect the southern flow of water along the coast.