Relative dating concept
Relative dating concept - netvibes not updating
Using these key or index fossils as markers, geologists began to identify a particular layer of rock wherever it was exposed.
Each year a tree adds a layer of wood to its trunk and branches thus creating the annual rings we see when viewing a cross section.Teaching about Earth's history is a challenge for all teachers.Time factors of millions and billions of years is difficult even for adults to comprehend.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).The concept is considered by uniformitarian geologists to be a major breakthrough in scientific reasoning by establishing a rational basis for relative time measurements.
However, unlike tree-ring dating -- in which each ring is a measure of 1 year's growth -- no precise rate of deposition can be determined for most of the rock layers.Wide rings are produced during wet years and narrow rings during dry seasons.This technique has posed a different problem for creationists, as this dating method does not make use directly of accelerated decay.From the results of studies on the origins of the various kinds of rocks (petrology), coupled with studies of rock layering (stratigraphy) and the fossils they contain (paleontology), geologists have associated layers of rocks with sequence of events thought to have occurred over hundreds of millions of years.For example, it is believed that during a particular episode the land surface was raised in one part of the world to form high plateaus and mountain ranges.However, "relative" dating or time can be an easy concept for students to learn.