Archean microfossils showing cell division from the swaziland system of South Africa.

A newly discovered population of organic walled microstructures from the Swaziland System, South Africa, is considered to be biological on the following grounds: (i) the structures are carbonaceous and occasionally have internal organic contents; (ii) the population has a narrow unimodal size frequency distribution (average diameter, 2.5 micrometers; range, 1 to 4 micrometers); (iii) the structures are not strictly spherical, but are commonly flattened and folded like younger microfossils; (iv) the sedimentary context is consistent with biogenic origins; and (v) various stages of binary division are clearly preserved.