Pre·cam·bri·an /priːˈkæmbriən/ adjective
belonging or relating to the period of time in the Earth's history from about 4,600 million years ago, when the hard outer surface of the Earth first formed, until about 570 million years ago, when simple forms of life first appeared on the Earth:
Precambrian rocks

[TahlilGaran] Dictionary of Contemporary English ▲