Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata.Once students begin to grasp "relative" dating, they can extend their knowledge of geologic time by exploring radiometric dating and developing a timeline of Earth's history.Using relative dating the fossil is compared to something for which an age is already known.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.
There are two basic approaches: relative age dating, and absolute age dating.
Time factors of millions and billions of years is difficult even for adults to comprehend.
However, "relative" dating or time can be an easy concept for students to learn.
Geologists generally know the age of a rock by determining the age of the group of rocks, or formation, that it is found in.
The age of formations is marked on a geologic calendar known as the geologic time scale.If a geologist claims to be 45 years old, that is an absolute age.Superposition: The most basic concept used in relative dating is the law of superposition.Simply stated, each bed in a sequence of sedimentary rocks (or layered volcanic rocks) is younger than the bed below it and older than the bed above it.This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.