Hope this Helps
This is what I have for my notes
The age of the Earth is estimated approximately 4500 - 5000 million years old. Scientists gained informaton about life in the past through varying types of fossil evidence and placed it onto a geological time scale. This is divided into periods depending on the succession of life. The end of a division is marked by the extiniction events. The different periods lasted different lengths of time and were established through the fossil record of plants and animals.
You don't need to know the periods just about the geological time scale and how it was established.
Hope that Helps
Edwina
xoxox