Precambrian Eon

The precambrian eon took place from 4.5 billion to 540 million years ago, it is not a unified time period because it makes up 7/8 of the earths history. At the beginning of the precambrian period the earth was only forming. About 2.5 bya oxygen was introduced into the atmosphere which gave way for life to evolve. Around 1.6bya eukaryotic cells appeared. Later in the earths history eukaryotic cells would make up fungi, plants, protests and modern animals. However, during the precambrian period only bacteria, stromatalites and multicellular algea were formed. Stromatalites are rocky mounds of microorganisms that use light energy and produce oxygen through photosynthesis. Vast amounts of stromatalites covered the earths surface and cleared co2 from the air, changing the earth dramaticaly. Prior to the formation of stromatalites the earths plates began to shift and the first super continent rodinia was formed. Eventually, 650 mya a mile thick sheet of ice covered the earth. At the end of the precambrian period, volcanic activity split the continent apart and co2 caused the ice sheets to draw back.