Seriation sequence dating
There are several synonyms used for each of these names in different parts of Europe, Asia and Americas but to avoid complications we will use the Alpine names only.The estimation of dates of 5 million to 500,000 years is done through a radio-active isotope disintegration technique known as Potassium- Argon method while dates upto 90,000 years are done by a similar method based on Carbon isotopes.The enormous amount of water trapped in the land borne ice caused severe lowering of the sea level exposing land bridge between many islands and their adjoining main lands.In many favourable coasts these ancient beaches have been found and named corresponding to the Alpine glacial order.The prehistoric units for the measurement of time are mainly in the form of a variety of climatic events of worldwide nature and hence these can never be as precise as our calendric units.One of the most important involvements of most prehistorians, therefore, lies in reconstructing the past climates of a given area and then correlating this with a broad successional sequence of worldwide events in order to pin the new area within a specific stage of this sequence.We shall briefly enter into all these dating techniques just for a basic awareness of the beginner, because in most cases these principles and actual working are very much outside the area of interest of average prehistorians: One of the simplest approaches to chronology is based on the principle that the lowest layer in any natural process of deposition is older than the ones above it (provided there has been no disturbance).The youngest phenomenon under the same logic will be represented by the topmost layer.
In Europe the glaciers have been identified by giving them names of rivers on the Alps.
Pleistocene epoch is marked by a rhythm of several glacial advances over Euro-Asia and the Americas.
All these periods of glacial advances were not of equal intensity neither were the intervening warm periods of the same type.
The calendar is a product of our civilization which measures the past in such units as years, month and days.
In dealing with prehistory such units are hopelessly useless and hence new units are required to be defined.