The most ancient evidence of photosynthetic structures, discovered within a set of microfossils dating back 1.75 billion years, is detailed in a paper published in Nature. This finding contributes valuable insights into the evolutionary history of oxygenic photosynthesis.
Oxygenic photosynthesis, a process unique to cyanobacteria and certain eukaryotic organelles, involves the conversion of water and carbon dioxide into glucose and oxygen through sunlight. Cyanobacteria played a significant role in early life evolution, particularly during the Great Oxidation Event around 2.4 billion years ago. However, the precise timing of the origins of oxygenic photosynthesis remains a subject of debate due to limited evidence.
In a recent study by Catherine Demoulin, Emmanuelle Javaux, and their team, direct evidence of fossilized photosynthetic structures from Navifusa majensis was presented. These microstructures, identified as thylakoids—membrane-bound structures found within chloroplasts of plants and some cyanobacteria—were discovered in fossils from three different locations. The oldest of these fossils, originating from the McDermott Formation in Australia, dates back 1.75 billion years.
N. majensis is presumed to be a cyanobacterium. The identification of thylakoids in a specimen of this age suggests that photosynthesis likely evolved before the 1.75 billion-year mark. However, the mystery of whether photosynthesis emerged before or after the Great Oxidation Event remains unsolved.
The authors propose that conducting similar ultrastructural analyses on older microfossils could provide answers and contribute to understanding whether the evolution of thylakoids played a role in the increase of oxygen levels during the Great Oxidation Event.