Relative dating principles include
Geologists have divided the Earth's history into Eras -- broad spans based on the general character of life that existed during these times -- and Periods -- shorter spans based partly on evidence of major disturbances of the Earth's crust.
The "relative" positions of layers and fossils to assign estimated dates to strata.
Between the years of 17, James Hutton and William Smith advanced the concept of relative dating.
Visible light and dark rings can be found in such cores that are then analyzed to determine the age of the ice.Therefore, the actual length of geologic time represented by any given layer is usually unknown or, at best, a matter of opinion.William Smith's collecting and cataloging fossil shells from rocks led to the discovery that certain layers contained fossils unlike those in other layers (see: fossil sorting).After the uplift of the land, the forces of erosion attacked the highlands and the eroded rock debris was transported and redeposited in the lowlands.
During the same interval of time in another part of the world, the land surface subsided and was covered by the seas.
He concluded, after studying rocks at many outcrops, that each layer represented a specific interval of geologic time.