Large and robust lenticular microorganisms on the young Earth

Our results support interpretations that the KF forms are bona fide, organic Archean microfossils and represent some of the oldest morphologically preserved organisms on Earth. The combination of morphology, occurrence, and δ13C values argues that the lenticular forms represent microbes that had planktonic stages to their life cycles. The similarity in morphology, δ13C, and facies associations among specimens from Australia and South Africa suggests that the lenticular microfossils on the two continents represent related organisms. The biological success of these organisms is demonstrated by their abundance, widespread distribution, and the fact that, as a group, they appear to have been present at least 400 million years. This success may be due in part to their robust structure and planktonic habit, features that may have contributed to survival on a young planet. Isotopic results further suggest that the lenticular organisms were autotrophs, an interpretation supporting the view that autotrophic metabolisms developed early on the young Earth.