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.Since there is no set rate of deposit for these layers, the actual length of time represented by these layers is a good guess.
First, we must understand they are dating the rocks and other materials found on the Earth to determine this.
There are two basic types of dating methods geologists rely on, Relative Time Dating and Absolute Time Dating.
In Relative Time dating a specific age in years is not given.
This type of dating puts events in their correct chronological order based upon the sedimentary layer in which an object is found.
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.
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.
Sedimentary rocks build up layers from the oldest deposits, at the bottom with the newest at the uppermost layers. Biostratigraphy is a specialized form of Stratigraphy, which uses plant and animal fossils to establish the different layers.