Archean Eon
The Archean begins with the formation of the Earth's crust с 3.8 billion years ago and extends to с 2.5 billion years ago, up to the start of the Proterozoic Eon, the second division of the Precambrian Period. The earliest and most primitive forms of life (bacteria and cyanobacteria) originated с 3.5 billion years ago in the middle of the Archean Eon (the Archean's alternative name, Archeozoic, means "ancient life"). Here are 25 Key facts about this Eon: 1. **Age and Duration:** The Archean Eon comprises about 1.5 billion years of Earth's history. 2. **Formation of Earth:** It began after the formation of Earth around 4.6 billion years ago. 3. **Atmosphere:** During the Archean, the atmosphere lacked free oxygen, consisting mainly of methane, water vapor, and nitrogen. 4. **Continental Crust Formation:** The Archean witnessed the formation of the first continental crust, essential for shaping the Earth's surface. 5. **Formation of Oceans:** Oceans formed duri...