Proterozoic

The Proterozoic is one of the most crucial periods in Earth’s history as it witnessed the first major increase in atmospheric oxygen levels (the Great Oxidation Event) and the rise of the first complex life forms. Early in this era, cyanobacteria continued to release oxygen into the atmosphere, which eventually overwhelmed the Earth’s ability to absorb it, leading to a gradual buildup of oxygen in both the oceans and the atmosphere. This process led to the extinction of many anaerobic organisms that thrived in low-oxygen environments but paved the way for the evolution of aerobic life. 

During the Mesoproterozoic and Neoproterozoic eras, tectonic activity resulted in the formation and break-up of the supercontinent Rodinia. Glaciations during the Neoproterozoic, including the “Snowball Earth” episodes, may have been among the most extensive ice ages in Earth’s history, potentially covering the entire planet in ice for millions of years. 

The Proterozoic also saw the emergence of the first eukaryotic organisms, which later gave rise to multicellular life. Fossils from this period, such as the Ediacaran biota, provide evidence of the first complex, multicellular organisms that would eventually lead to the explosion of life in the Cambrian period.