The early evolutionary stages of the geosphere and biosphere are determined by three interrelated factors: (1) continuous cooling of the surface and interior (mantle) of the Earth (the mean temperatures of the mantle and surface decreased by a factor of 1.5-2 and 3-4, respectively; the mean heat flow was reduced by approximately one order of magnitude, and viscosity, by three orders); (2) continuous stepwise oxidation of the surface, which was particularly well pronounced from 3.8 to 1.8 Ga; and (3) periodic and correlated fluctuations of conditions in the geosphere and biosphere of varying extent and nature. The major boundaries of this evolution were about 4 Ga (the origin of rather thick and heterogeneous earth's crust, the origin of life); about 3 Ga (appearance of a strong magnetic field, an increase in photosynthetic activity); about 1.8-1.9 Ga (appearance of an oxidized atmosphere, the first supercontinent, possibly, the first superplumes from the nucleus); and about 0.75 Ga (acceleration of subduction, "watering" of the upper mantle, elevation of continents with vast land masses, shelves, large rivers, and the first great glaciations). The significance and correlations of the earliest events (before and about 4 Ga) and events about 750 Ma are widely debated. In the Late Archean and Early Proterozoic (before 1.8 Ga), the biosphere was dominated by cyanobacteria, the dynamics and developmental peaks of which are marked by the presence of widespread stromatolite buildups in carbonaceous rocks (initially, mostly dolomitic matter). About 700-750 Ma, intense and frequent glaciations developed, marking the cooling of the Earth.
