Proterozoic Period
2.5 billion-541 million years ago
About this Period
First complex cells and multicellular life
The Proterozoic eon was a time of crucial biological and geological transitions, witnessing the rise of complex life and dramatic changes to Earth's atmosphere.
Three revolutionary developments defined this era: the rise of eukaryotic cells (cells with nuclei), the evolution of sexual reproduction, and the emergence of the first multicellular organisms. The Great Oxidation Event occurred early in this period, dramatically increasing atmospheric oxygen and fundamentally changing Earth's chemistry.
Near the end of this eon, the mysterious Ediacaran biota appeared—the first complex animals, including strange soft-bodied organisms unlike anything alive today. Several "Snowball Earth" events also occurred, with ice potentially covering the entire planet.
The Proterozoic bridged the gap between simple microbial life and the explosion of complex organisms that would follow.
