Archean eon or Archaeozoic is the second division of the Precambrian time.
Time Period: It began around 4 billion years ago and extended till the beginning of Proterozoic eon 2.5 billion years ago.
Features:
♦ There were many volcanic gases in the atmosphere, but the dominating gas was carbon dioxide and the level of oxygen was very low.
♦ The first photosynthesising organisms had evolved by the end of this eon. They started to produce oxygen, which eventually changed the environment on the Earth.
♦ In the Archean eon, the rocks were mostly igneous or metamorphic, but from this period onwards the sedimentary rocks also started forming in the ocean.
