Charred bones are better preserved and are therefore relatively more reliable.Charcoal is best material specially if derived from short live plants.Sir Flinders Petrie had worked out a formula for dating the finds on the basis of the thickness of the deposit.According to him a period of hundred years may be granted for the accumulation of a deposit of one and a half feet.Quite convincing dates are sometimes arrived at by importing parallels from other contemporaneous cultures.This parallelism is formed due to trade relations, particularly wehen trade followed in both directions.Astronomical data have been applied in the study of geological ice ages by calculating the curves for major fluctuation of solar radiation.
For example charcoal, wood, shell, paper, leaves, cloth, animal hair, bone, pollen, tooth, iron, prehistoric soot from the ceiling of the caves practically any material containing some carbon can be subjected Bones are generally affected by ground water carbonates and are therefore least reliable for dating.
For example, beads closely resembling those from the temple repositories at Cnoss and dating from C.1600 B.
C were found in a late context (Period V) at Harappa. By noting the association of these beads it has been possible to trace a archaeological datum line across Indian sub-continent and Mesopotamia.
This closely agrees with the fact that the seals from Indus Valley style from Ur, Kish and Tell Asmar and other sites fall within the range of 2500-1500 B. When a group or type of objects are found together under circumstances suggesting contemporanity they are said to be associated.
It is nearly always association with other phenomena that gives a first clue as to the use, the age and chronological attribution of a potential datum, but age at least may sometimes be inferred from position in a geological deposit or a layer of peat.
However this formula has not been accepted by many archaeologists.