The Precambrian System is also called the ‘Pre-Cambrian System’ or ‘Pre-Palaeozoic Erathem’. The Precambrian System is not a formal chronostratigraphic unit. It refers to the rocks that formed from the beginning of the Earth’s history to the early Cambrian Period, and this period is called the Precambrian Period. Based on isotopic age dating, it is estimated that the Earth began to form approximately 4.6 billion years ago. The Precambrian Period covers at least four billion years, which accounts for nearly 90% of the Earth’s history.