A fossil found in Australia suggests photosynthesis evolved at least 1.75 billion years ago. 

Microscopic fossils from the McDermott Formation in the southern McArthur Basin in the NT contain the oldest photosynthetic structures ever discovered, shedding light on the origins of photosynthesis, according to Belgian research.

Oxygenic photosynthesis, in which sunlight catalyses the conversion of water and carbon dioxide into glucose and oxygen, is almost unique to cyanobacteria.

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 due to limited evidence.

Catherine Demoulin, Emmanuelle Javaux and colleagues have presented direct evidence of fossilised photosynthetic structures from Navifusa majensis. 

The microstructures are thylakoids; membrane-bound structures found inside the chloroplasts of plants and some modern cyanobacteria. 

The authors 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.

N. 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 Oxidation Event. 

Similar ultrastructural analyses of older microfossils could help to answer this question, the authors say, and help to determine whether the evolution of thylakoids contributed to the rise in oxygen levels at the time of the Great Oxidation Event.

The full study is accessible here.