The 1.75 billion-Year Secret to the Origin of Life

In a groundbreaking discovery, scientists have identified the earliest direct evidence of photosynthesis on Earth, hidden within tiny fossils dating back a staggering 1.75 billion years. The findings offer critical insights into the evolution of photosynthetic organisms and the role they played in shaping the Earth’s early ecosystems.

Researchers led by palaeomicrobiologist Catherine Demoulin of the University of Liège uncovered these remarkable structures within the cells of cyanobacteria (Navifusa majensis) fossils from the McDermott Formation in northern Australia, dating back to 1.75 billion years ago.

Within the organelles known as chloroplasts, there exists a membrane system called thylakoid, comprising interconnected vesicles. Chlorophylls, pigments that absorb light for the process of photosynthesis, are located on this membrane system. A similar structure is also present in certain cyanobacteria.

The significance of this discovery lies in its implications for understanding the origins of oxygenic photosynthesis, a process that led to the development of complex life forms. Oxygenic photosynthesis, performed by green algae and higher plants is also is unique to one group of bacteria: the cyanobacteria. The newfound evidence provides a minimum age for the divergence of thylakoid-bearing cyanobacteria, shedding light on the coevolution of Earth and life.

The study’s lead author, Catherine Demoulin, emphasized the importance of these findings, stating, “Our study provides direct evidence for the presence of metabolically active cyanobacteria performing oxygenic photosynthesis.” The discovery opens a new avenue for exploring the evolution of early Earth ecosystems by providing a tool to decipher the palaeobiology of ancient cells.

Photosynthesis, a process where sunlight is used to convert water and carbon dioxide into glucose and oxygen, forms the foundation of life on Earth. The newly discovered fossils push the record of thylakoids back by 1.2 billion years. The finding implies that oxygenic photosynthesis predates the Great Oxidation Event, which marks a sudden increase in oxygen levels in the Earth’s atmosphere approximately 2.4 billion years ago. The event’s precise cause is unclear, but the emergence of photosynthetic organisms is considered the strongest contributor.

The researchers used high-resolution microscopy techniques to analyse fossils from two different locations: the McDermott Formation in Australia and the Grassy Bay Formation in Canada. The fossils, less than a millimetre in size, were carefully sliced into thin sections for examination. The presence of thylakoids in these ancient cyanobacteria fossils extends our understanding of the evolution of photosynthesis and raises intriguing questions about its role in shaping Earth’s early environments.

Could photosynthesis have evolved in time to trigger the Great Oxidation Event? While the researchers’ discovery provides an important piece of the puzzle, the key to answering this question lies in the exploration and analysis of older fossils. The microscopic revelations from these ancient single-celled organisms offer a captivating glimpse into Earth’s phototrophic past and the intricate dance between life and the environment.