Upon completion of this lesson, students should be able to:The age of the earth has been estimated about 4.6 billion years. A time scale that covers the earth’s history from its origin to the present is called geological time scale. The chronology is divided into hierarchy of time intervals: Eons, Eras, Periods and Epochs. This note is description on how geological time period of earth is differentiated. The origin of the earth is directly related to the origin of the solar system as the earth is a member of the solar system. This note has different hypothesis regarding origin of the earth. The dead bodies of plants and animals hardened and preserved in sedimentary rocks are called fossils. Tracing, mould, cast and a remaining skeleton or parts of the skeleton of dead bodies are different forms of fossils.