Seminar

The advent of oxygenic photosynthesis in ancient cyanobacteria is one of the most important events in the evolutionary history of life. Scytonemin is a yellow-brown UV-filtering pigment widely distributed in cyanobacteria species. In consideration of its stable physical and chemical properties against degradation, scytonemin is evaluated as the potential molecular biomarker for oxygenic photosynthesis for the first time. Extensive experimental Raman spectroscopic investigations indicate the absence of the diagnostic signals of scytonemin but the presence of kerogen in early Archean sedimentary rocks. To interpret this, a geochemical transformation model is proposed to simulate the evolution of scytonemin in sedimentary rocks, where the theoretical Raman approaches suggest that the derivatives of scytonemin are consistent with kerogen in terms of Raman signatures. Noted that the long evolutionary history of pigmentation and large quantity of UV-filtering pigments such as scytonemin could be produced in Archean, it is reasonable to suggest that scytonemin is probably the precursor of kerogen in early Archean sedimentary rocks.

It has long been accepted that the surficial environment of early Archean was uninhabitable because the protective ozonosphere that blocks UVC and most of UVB was absent. Ab initio calculations suggest that both scytonemin and its derivatives have significant UVC absorption. The experimental and theoretical results on scytonemin’s Raman activities and UV-absorbing properties clearly illustrate the evolutionary history of scytonemin in sedimentary environments and demonstrate its important role as key biochemical UV-screening material for the early Earth’s ecosystem. At last, I briefly introduce my work on an oxygen-free biochemical world, which is not much related to the previous part, but is interesting