The earliest known evidence of photosynthetic structures has been identified inside a collection of the enigmatic cylindrical microfossils Navifusa majensis from the 1.75-billion-year-old McDermott Formation in Australia.
Oxygenic photosynthesis, in which sunlight catalyses the conversion of water and carbon dioxide into glucose and oxygen, is unique to cyanobacteria and related organelles within eukaryotes.
Cyanobacteria had an important role in the evolution of early life and were active during the Great Oxidation Event around 2.4 billion years ago, but the timings of the origins of oxygenic photosynthesis are debated owing to limited evidence.
“Today oxygenic photosynthesis is unique to cyanobacteria and their plastid relatives within eukaryotes,” said University of Liège paleontologist Catherine Demoulin and her colleagues.
“Although its origin before the Great Oxidation Event is still debated, the accumulation of oxygen profoundly modified the redox chemistry of the Earth and the evolution of the biosphere, including complex life.”
“Understanding the diversification of cyanobacteria is thus crucial to grasping the coevolution of our planet and life, but their early fossil record remains ambiguous.”
In their study, Demoulin and co-authors found the fossilized photosynthetic structures in the Navifusa majensis microfossils.
The microstructures are thylakoids — membrane-bound structures found inside the chloroplasts of plants and some modern cyanobacteria.
The researchers identified them in fossils from three different locations, but the oldest, which come from the McDermott Formation in Australia, are 1.75 billion years old (Paleoproterozoic Era).
Navifusa majensis is presumed to be a cyanobacterium. The discovery of thylakoids in a specimen of this age suggests that photosynthesis may have evolved at some point before 1.75 billion years ago.
It does not, however, solve the mystery of whether photosynthesis evolved before or after the Great…
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