Proterozoic

The Proterozoic Eon is a major interval of Earth's history, spanning from about 2.5 billion to 541 million years ago. It lies between the Archean Eon, which hosts some of the earliest life, and the Phanerozoic Eon, characterized by abundant animal life. The Proterozoic is subdivided into Paleoproterozoic (2.5–1.6 Ga), Mesoproterozoic (1.6–1.0 Ga), and Neoproterozoic (1.0 Ga–541 Ma).

The Paleoproterozoic witnessed the Great Oxygenation Event, beginning around 2.4 Ga, which raised atmospheric oxygen and altered planetary chemistry. This shift contributed to changes in mineral deposits, such as a decline in banded iron formations and the appearance of red beds, and it coincided with major crustal growth and the stabilization of early continental blocks. The supercontinent Columbia (Nuna) began to assemble during this interval.

In the Mesoproterozoic, continental crust continued to mature and stabilize, with the Nuna/Columbia landmass persisting. The biosphere saw the diversification of eukaryotic life, with evidence for more complex cellular organization and the spread of multicellular forms as the era progressed.

The Neoproterozoic era features dramatic climatic swings, including the Cryogenian ice ages that may have encompassed widespread glaciation. Toward its end, the supercontinent Rodinia assembled and later broke apart, giving way to the formation of Pannotia near its close. The late Neoproterozoic also records a rise in multicellular life, culminating in the Ediacaran biota and precedents to the Cambrian explosion. The Proterozoic ends with the base of the Phanerozoic, about 541 Ma, marking the onset of abundant animal life.