In a groundbreaking discovery, tiny microfossils encapsulated in ancient rocks for nearly 2 billion years have provided the earliest evidence of photosynthesis on Earth. Researchers exploring the McDermott Formation in the desert of northern Australia have identified thylakoids within what are believed to be fossilized cyanobacteria dating back 1.75 billion years.
Thylakoids, microscopic structures found within the cells of present-day photosynthetic organisms containing chlorophyll, are vital for absorbing light during photosynthesis. This revelation marks the oldest direct evidence of photosynthesis, offering a new benchmark for the emergence of thylakoid-bearing cyanobacteria and providing a valuable tool for comprehending early Earth ecosystems and the origins of life on our planet.
The study, led by paleomicrobiologist Catherine Demoulin of the University of Liège, emphasizes the metabolic activity of cyanobacteria engaging in oxygenic photosynthesis. This finding opens the door for a detailed analysis of other fossils, potentially identifying similar structures and pinpointing the integration of photosynthesizing structures by early complex algal cells.
While photosynthesis may seem like a discreet process confined to plants and algae, it serves as the foundation for the survival of nearly all living organisms. Photosynthetic organisms not only form the basis of food webs but also contribute to the oxygenation of Earth’s atmosphere, crucial for supporting life.
The research sheds light on the Earth’s evolutionary history when atmospheric and oceanic oxygen levels were low. The Great Oxidation Event, around 2.4 billion years ago, microfossils witnessed a sudden surge in oxygen levels. The emergence of photosynthetic organisms is one potential explanation for this event.
While the earliest undisputed evidence of cyanobacteria dates back to 2.018 billion years ago, the internal structures of fossils often do not survive intact, and not all cyanobacteria species possess thylakoids. Demoulin and her team utilized advanced microscopy techniques to examine microfossils of Navifusa majensis, a cyanobacteria species. Thylakoid membranes were identified within the single-celled organisms from fossil beds in the Grassy Bay Formation (Canada) dating up to 1.01 billion years ago and the McDermott Formation (Australia) stretching as far back as 1.75 billion years ago.
This extends the fossil record of thylakoids by an impressive 1.2 billion years, indicating the evolution of oxygenic photosynthesis occurred before this time. However, the question of whether it contributed to the Great Oxidation Event remains unanswered. The researchers suggest that further exploration and analysis of even older fossils may provide insights into this intriguing chapter in Earth’s history.
“The discovery of preserved thylakoids within N. majensis reported here provides direct evidence for a minimum age of about 1.75 billion years ago for the divergence between thylakoid-bearing and thylakoid-less cyanobacteria,” the researchers wrote. “We predict that similar ultrastructural analyses of well-preserved microfossils might expand the geological record of oxygenic photosynthesizers and of early, weakly oxygenated ecosystems in which complex cells developed.” The research has been published in Nature.
Edited by: Vaishali Verma
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