The topic of chronostratigraphy involves the setting of a time scale for the dating of various geological processes. The chronostratigraphic map represents the age of rocks and their classification in different phases of the Earth's history. Rock masses are dated using organic and inorganic characteristics and content, ordered chronologically according to their order of formation and inserted in the time scale. It is possible to differentiate between relative and absolute dating.
Relative age is given by lithostratigraphy, based on information concerning the sequence of the rock layers. Generally, younger layers have been deposited on older layers, so that for undisturbed states the spatial sequence from bottom to top corresponds to the temporal formation from older to younger rocks.
With help from biostratigraphy, rock masses may be compared among regions and sometimes world-wide. Biostratigrapahy is based on the comparison of the remains of plants and animal organisms (fossils) which have gradually developed in various species during the history of the Earth (evolution).
The absolute age of rocks, i.e. information given in years and millions of years, comes from radiometric dating. This method takes advantage of the radioactive decay of small amounts of radioactive isotopes in rocks. Age values may be calculated from the relation between remaining radioactive isotopes and the product of radioactive decay in the rocks.
The subdivision of the Swiss territory into the Jura, the Plateau and the Alps reflects the spatial distribution of ages of the rocks. The oldest, paleozoic and, in part, pre-Cambrian, rocks are located in the central and southern Alps; they belong to the crystalline basement (part of the continental crust) and were involved in orogeneses before that of the Alps. In the northern part of the Alps, in narrow internal zones and in the Bergamo Alps, mostly mesozoic rocks outcrop. These overthrusted and folded sediments, as well as remains of the oceanic crust, were deposited in the pre-Mediterranean Tethys. The mesozoic rocks, which form the Jura and the adjacent north-western plateau were also deposited on the northern shelf of the Tethys. Tertiary rocks characterise the Plateau; they are also located on the Po Plain and in the Upper Rhine Graben. These are erosion products of the forming alps, which are termed molasse in the Plateau. The youngest deposits are the quaternary sediments, which may be observed in areas where glaciers were located in the glacial periods and in valley fill material.