According to this system, humans passed through three distinct stages of technological development, based on the primary material used to manufacture tools and weapons: the Stone Age, the Bronze Age, and the Iron Age.
However, as the basic principles of relative dating progressed during the course of the 19th cent., investigators were able to correctly determine the relative age of many archaeological and geological materials.
Stratigraphic dating is accomplished by interpreting the significance of geological or archaeological strata, or layers.
The method begins with the careful drawing and description of strata (the geological or archaeological profile).
The profile from one location is then compared with profiles from surrounding sites.
Other techniques are occasionally useful, for example, historical or iconographic references to datable astronomical events such as solar eclipses (archaeoastronomy).
When archaeologists have access to the historical records of civilizations that had calendars and counted and recorded the passage of years, the actual age of the archaeological material may be ascertained—provided there is some basis for correlating our modern calendar with the ancient calendar.
Technological changes can be used for relative dating of archaeological material.
The three-age system devised by the Danish archaeologist Christian Thomsen in the 1830s made use of technological criteria.
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