Name describe two principles used relative dating rocks
Over time, as more areas were mapped and knowledge increased, the geological time-scale was developed, based on a wide range of rock and fossil occurrences.
Geological Time Units were subsequently devised, which placed particular groups of rocks and fossils into relative age categories.
Many of these time units are named after groups of strata that were first described from type localities in the British countryside (e.g. The last 542 million years to the present is known as the Phanerozoic (meaning "life presence") era.
It contains the most subdivisions in the geological time scale because this period in Earth history was teeming with recognisable and evolving plant and animal life.
Uniformitarianism is usually referred to by the more explanatory phrase "the present is the key to the past".The study of rock layers preserved in the geological record is called stratigraphy (Figure 1).The two principles of stratigraphy allow the relative age of rocks in a stratigraphical sequence to be determined.The boundaries between geological time units of the Phanerozoic era are marked by widespread extinctions in the fossil record and by major unconformities in the rock sequence that signify global events, such as major magmatic episodes and meteorite impacts events.Examples include the voluminous global outpourings of magma at the end of the Permian and Cretaceous periods, and a meteorite impact at the end of the Cretaceous.
In simple terms, a geological map shows the surface distribution of rocks in a particular area.