This process lead to a system of time containing eons, eras, periods, and epochs all determined by their position in the rock record.For example, rocks of the Phanerozoic eon are found on top of rocks from the Proterozoic eons therefore rocks of the Phanerozoic are younger than rocks of the Proterozoic.Relative time places events or formations in order based on their position within the rock record relative to one another using six principles of relative dating.Relative time can not determine the actual year a material was deposited or how long deposition lasted; it simply tell us which events came first.
Steno put forth still another idea—that layered rocks were likely to be deposited horizontally.
His principle of superposition of strata states that in a sequence of strata, as originally laid down, any stratum is younger than the one on which it rests and older than the one that rests upon it.
..that within a sequence of layers of sedimentary rock, the oldest layer is at the base and that the layers are progressively younger with ascending order in the sequence.
This is termed the law of superposition and is one of the great general principles of geology. This principle would seem self-evident, but its first enunciation more than 300 years ago by Nicolaus Steno represented an enormous advance in understanding.
Ordinarily, beds of sedimentary rocks are deposited more or less horizontally. Known as the principle of superposition, it holds that in a series of sedimentary layers or superposed lava flows the oldest layer is at the bottom, and layers from there upward become progressively younger. ...rocks demonstrated superpositional relationships: rocks deposited first lie at the bottom of a sequence, while those deposited later are at the top.
The most obvious feature of sedimentary rock is its layering.