Eons (an extremely long period of time; thousands of years)
Eons In geochronology , time is generally measured in mya ( megayears or million years), each unit representing the period of approximately 1,000,000 years in the past. The history of Earth is divided into four great eons , starting 4,540 mya with the formation of the planet. Each eon saw the most significant changes in Earth's composition, climate and life. Each eon is subsequently divided into eras , which in turn are divided into periods , which are further divided into epochs . EonTime (mya)Description Hadean 4,540–4,000The Earth is formed out of debris around the solar protoplanetary disk . There is no life. Temperatures are extremely hot, with frequent volcanic activity and hellish environments. The atmosphere is nebular. Possible early oceans or bodies of liquid water. The moon is formed around this time, probably due to a protoplanet's collision into Earth . Archean 4,000–2,500 Prokaryote life, the first form of...