The discovery of microfossils in a collection of 1.75 billion-year-old Australian rocks could shed light on the evolution of oxygenic photosynthesis.
Photosynthesis is how plants and some bacteria convert water and carbon dioxide into glucose and oxygen using sunlight.
The chemical process is the earth's major producer of both oxygen and organic matter and a principal player in the development and maintenance of life.
Flemish scientists found fossilised photosynthetic microstructures known as thylakoids, which are also found inside plant cells and some modern cyanobacteria, in tiny fossils called Navifusa majensis at three different locations.
The oldest, which are 1.75 billion years old, came from the southern McArthur Basin in the Northern Territory.
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 timing of the origins of oxygenic photosynthesis is debated owing to limited evidence.
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.
Microfossils are the tiny remains of bacteria, protists, fungi, animals, and plants found in rock.
The research was published in the scientific journal Nature on Thursday.
