Types of relative dating
The following chart shows this concept with a brief description of each age represented.
The age of a rock in years is called its absolute age.
Smith noticed that specific forms of life were fossilized in particular layers of rock, giving a time line story indicating when, in time, events occurred.
This progression of or evolution of life occurred in a vertical fashion up through the layers.
Where do scientists begin the story of Earths history?
One place to start is by looking at the age of the materials that make up the Earth itself.
The Principle of Lateral Continuity: Because rock layers cover large areas of the Earths surface, scientists can relate layers in one location to another.
In the late 18 century, James Hutton developed the idea that the layers found in rock outcrops were representations of the story of time on the planet.
He concluded, the bottom most layers were deposited first, thus making them the oldest and subsequent layers were progressively younger in age.
When scientists are able to determine the age of rocks and fossils, they can then tell a more accurate story of the Earths history.
When Geologists and other scientists refer to the age of the Earth, they are using one of two methods to determine this.