Small fossils, trapped for nearly two billion years in pieces of ancient rocks, provide the first evidence of the process of photosynthesis on Earth. In the "McDermott" formation in northern Australia, small structures called thylakoids have been discovered in what is believed to be fossilized cyanobacteria dating back 1.75 billion years. While this may seem complex, it relates to cellular structures capable of converting sunlight, water, and carbon dioxide into energy and oxygen. The oldest fossil containing direct evidence of structures for oxygenic photosynthesis dates back to about half a billion years ago. However, this new discovery pushes the timeline back by 1.2 billion years.
The University of Liège in Belgium reported that a group of scientists identified fundamental structures for producing oxygenic photosynthesis within fossilized microorganisms that date back 1.75 billion years, representing the oldest fossil evidence of this vital metabolic process. These structures are very simple in the broad spectrum of life on Earth today, but they were incredibly crucial to the Great Oxidation Event (or Great Oxygenation), an important historical period on our planet that helped fill the atmosphere with breathable air, enabling life forms to thrive.
It is believed that the earliest forms of life on Earth did not require oxygen for survival, as the planet's primordial atmosphere consisted mainly of carbon dioxide, methane, and water vapor, rather than nitrogen and oxygen, which make up the current atmosphere. However, about 2.4 billion years ago, there was the Great Oxidation Event, during which oxygen levels in Earth’s atmosphere rose significantly for the first time. Some scientists have suggested that the evolution of thylakoid membranes in early cyanobacteria provided the necessary driving force for photosynthesis to catalyze this event.
Cyanobacteria are a type of microorganism that obtains energy through oxygenic photosynthesis, during which water and carbon dioxide are converted into glucose and oxygen. Thylakoids are a group of interconnected structures associated with the membrane and integrated into chloroplasts (a type of plastid found in plant cells) and some modern cyanobacteria. The thylakoid structures are present within the cells of organisms conducting photosynthesis today, containing chlorophyll pigment used to absorb light for the photosynthesis process. This means that the microscopic fossils represent the oldest direct evidence of the photosynthesis process, giving us a new minimum age for the emergence of thylakoid-bearing cyanobacteria and a new tool for understanding the ecosystems of early Earth and how life emerged on our planet.
However, there is still debate over the origin of the process of oxygenic photosynthesis, as well as the type of cyanobacteria involved in the early oxygenation of Earth. In a recent study published in the journal Nature, traces of thylakoid membranes were reported in the microscopic fossils known as Navifusa majensis, found in sedimentary rocks discovered in the McDermott formation in northern Australia, as well as in another sample from Canada dating back up to 1.01 billion years.
According to the study's authors, observations allowed the identification of Navifusa majensis as fossilized cyanobacteria. Professor Emmanuel Javaux, a co-author of the study from the University of Liège, explained to Vice magazine that the discovered structures allow us to unequivocally determine that the Navifusa majensis group "was actively performing early oxygenic photosynthesis before 1.75 billion years ago."
Scientists plan to carefully search for and study ancient fossils to verify that thylakoid membranes were involved in the oxygenation of our planet during the Great Oxidation Event. Javaux stated, "If we are interested in the early version of our planet and its life, then these cyanobacteria are extremely important microorganisms because they invented the process of oxygenic photosynthesis," emphasizing that this process "changed the chemistry of the Earth over time," leading to the early evolution of life. The new study has been published in the journal Nature.
