In a groundbreaking revelation, the earliest evidence of photosynthetic structures has emerged within a collection of microfossils dating back a staggering 1.75 billion years, as detailed in a recent Nature paper. This discovery offers a crucial glimpse into the evolutionary history of oxygenic photosynthesis.
Oxygenic photosynthesis, a process unique to cyanobacteria and certain eukaryotic organelles, involves harnessing sunlight to convert water and carbon dioxide into glucose and oxygen. While cyanobacteria played a pivotal role in the early evolution of life and were active around the Great Oxidation Event approximately 2.4 billion years ago, the exact timing of the origins of oxygenic photosynthesis has remained a subject of debate due to limited evidence.
Catherine Demoulin, Emmanuelle Javaux, and their colleagues present a significant breakthrough by providing direct evidence of fossilized photosynthetic structures within Navifusa majensis. These microstructures, identified as thylakoids—membrane-bound structures found in the chloroplasts of plants and certain modern cyanobacteria—were uncovered in fossils from three distinct locations. Notably, the oldest specimens, originating from the McDermott Formation in Australia, date back 1.75 billion years.
N. majensis, presumed to be a cyanobacterium, unveils the possibility that photosynthesis might have evolved before the 1.75 billion-year mark. However, the mystery of whether this evolution occurred before or after the Great Oxidation Event persists.
The authors propose that conducting similar ultrastructural analyses on even older microfossils could hold the key to resolving this enigma. Such investigations might unveil whether the evolution of thylakoids played a role in the surge of oxygen levels during the Great Oxidation Event, contributing to our understanding of this pivotal juncture in Earth’s history.
Source: Nature Publishing Group