Ellipsoidal Microstructures of Narrow Size Range in the Oldest Known Sediments on Earth

The sedimentary rocks within the Onverwacht Group, which show little or no metamorphic overprint, are the oldest known sediments on earth. Some of these sediments have been dated at ∼ 3.4 × 103 years old. Microscopic examination of petrographic thin sections of these sediments has revealed round or ellipsoidal shaped microstructures of 2μ to 6μ size range. These microstructures show what appear to be double walls and are found individually or in chains or clusters. They are resistant to hot 6N HC1, hot 48 percent HF, ozone and organic solvents. These forms could be organic particulate matter of no chemical or biological evolutionary significance, or they could be the precursors to the first living cell. Finally, they could be the oldest known microfossils on earth. Until ultramicro-chemical analyses are available on these particles, great caution is needed in the interpretation of their origin.