Paleoproterozoikum

The Paleoproterozoic is the first of three subdivisions of the Proterozoic eon, spanning from approximately 2.5 billion years ago (Ga) to 1.6 billion years ago (Ga). This era marks a critical period in Earth's history, characterized by significant geological, atmospheric, and biological changes that set the stage for the development of complex life.

During the Paleoproterozoic, the supercontinent Kenorland began to form, though its exact configuration remains debated among geologists. This era also witnessed the Great Oxidation Event, which occurred around 2.4 to 2.3 Ga. This event was driven by the proliferation of cyanobacteria, which produced oxygen as a byproduct of photosynthesis. The accumulation of oxygen in the atmosphere fundamentally altered Earth's chemistry, leading to the depletion of methane and the formation of the ozone layer, which provided protection against ultraviolet radiation. These changes created conditions more favorable for the evolution of aerobic organisms.

The Paleoproterozoic is also notable for the first appearance of banded iron formations (BIFs), sedimentary rocks composed of alternating layers of iron oxides and chert. These formations are evidence of the high concentrations of dissolved iron in ancient oceans, which were later oxidized by the rising oxygen levels. The era saw the development of more complex microbial life, including stromatolites, which continued to thrive in shallow marine environments.

By the end of the Paleoproterozoic, the atmosphere had stabilized with higher oxygen levels, and the stage was set for the Neoproterozoic, during which more complex multicellular life would emerge. The geological and atmospheric transformations of this era laid the foundation for the evolution of life as we know it today.