Mesoarchaean

The Mesoarchaean is a geologic eon spanning from 3,200 to 2,800 million years ago (Ma). It is the second of the four defined eons of Earth's history, following the Paleoarchaean and preceding the Neoarchaean. This period falls within the larger Archean Supereon. The Mesoarchaean represents a significant chapter in Earth's early development, characterized by ongoing continental formation and the emergence of early life forms.

During the Mesoarchaean, the Earth's crust continued to differentiate, leading to the formation of larger and more stable continental cratons. These nascent continents were smaller and more fragmented than the supercontinents that would form later in Earth's history. Volcanic activity remained prevalent, contributing to the thickening of the crust and the formation of new igneous rocks. The atmosphere at this time was still largely anoxic, lacking significant amounts of free oxygen.

Evidence from this eon points to the presence of early life, primarily prokaryotic microorganisms. Stromatolites, layered structures formed by the trapping and binding of sedimentary grains by microbial communities, are found in rocks dating to this period, indicating the existence of photosynthetic bacteria. These early life forms played a crucial role in the biogeochemical cycles of the primitive Earth. The geological record of the Mesoarchaean, though preserved in some of the oldest rocks on the planet, is often fragmented and altered by subsequent geological processes.