Mesoarchean

During the Mesoarchean, large portions of Earth’s landmasses were submerged beneath shallow seas, creating environments ideal for microbial life. Stromatolites from this period are some of the oldest evidence of widespread biological activity, primarily formed by communities of cyanobacteria. These microorganisms were likely engaging in photosynthesis, but the oxygen produced was absorbed by the ocean’s iron, forming banded iron formations (BIFs), which are still found in the geologic record today. 

The Mesoarchean epoch saw the formation of significant continental crusts, including the Kaapvaal and Pilbara cratons, which are now parts of South Africa and Australia, respectively. These cratons are among the oldest and most stable pieces of Earth’s continental lithosphere. The Mesoarchean is marked by continued volcanic and tectonic activity, although tectonic processes were different from modern-day plate tectonics due to the hotter mantle conditions.