They used pottery and other materials in sites to date 'relatively'.
They thought that sites which had the same kinds of pots and tools would be the same age.
Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.
Each isotope is identified with what is called a ‘mass number’.
"Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure.Geologists often need to know the age of material that they find.They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years.We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess." [Rasmus Nyerup, (Danish antiquarian), 1802 (in Trigger, 19)].The person who wrote these words lived in the 1800s, many years before archaeologists could accurately date materials from archaeological sites using scientific methods.
Geological Time | Geologic Time Scale | Plate Tectonics | Radiometric Dating | Deep Time | Geological History of New Zealand | Radiometric Dating Radiometric measurements of time Since the early twentieth century scientists have found ways to accurately measure geological time.