Paleoproterozoic

The Paleoproterozoic is a geologic era within the Proterozoic Eon, spanning roughly 2.5 to 1.6 billion years ago. It follows the Archean and precedes the Mesoproterozoic, and it is the first era of the Proterozoic in which continental crust became more widespread and geologic processes began to resemble more modern tectonics.

Biologically, the era witnessed the long-term buildup of atmospheric oxygen, largely due to cyanobacteria performing oxygenic photosynthesis. This Great Oxygenation Event, which occurred between about 2.4 and 2.0 Ga, transformed global redox conditions and led to widespread oxidation of iron in seawater, first recording as banded iron formations. The atmospheric and oceanic changes coincided with significant glaciations, notably the Huronian glaciations around 2.4–2.2 Ga, which are among the earliest well-documented ice ages on Earth.

Geologically, the Paleoproterozoic preserves some of the oldest recognizable crust and the development of early cratons, marking a shift toward more stable continental cores. The era contains extensive volcanic-sedimentary successions and BIF-rich sequences that record changing redox states and tectonic activity. While the fossil record from this interval is sparse, microfossils and chemical signatures indicate microbial life persisted and diversified.

By the end of the Paleoproterozoic, tectonic and environmental conditions had laid the groundwork for later biological and geochemical evolution, and the interval leads into the Mesoproterozoic with the continued growth of continental crust and further oxygenation of Earth's surface.