Scientists Uncover the Earliest Fossil Evidence of Photosynthesis

Nearly all animals need to breathe oxygen to survive. The life-sustaining gas they inhale is made by plants, algae and cyanobacteria during photosynthesis.

In a new study published Wednesday in the journal Nature, researchers have found cyanobacteria fossils from around 1.75 billion years ago that seem to have had the tools to make oxygen. They contain thylakoid membranes, structures in which photosynthesis takes place. The find marks the earliest fossil evidence of photosynthesis.

“This discovery extends the fossil record of such internal membranes by at least 1.2 billion years,” study co-author Emmanuelle Javaux, a biologist at the University of Liège in Belgium, tells Gizmodo’s Isaac Schultz.

Indirect evidence from genetics and chemical studies had previously suggested that cyanobacteria had thylakoids by this time. But exactly when the photosynthesizing structures first evolved remained unclear, Kevin Boyce, a paleobotanist at Stanford University who was not involved in the work, tells New Scientist’s Grace Wade. The new study, he adds, indicates that this occurred at least 1.75 billion years ago.

“Any evidence that you have from that time period is important, because the fossil record is really very sparse,” Patricia Sanchez-Baracaldo, an evolutionary microbiologist at the University of Bristol in England who did not contribute to the findings, tells Science News’ Tina Hesman Saey.

The first life on Earth didn’t require oxygen to survive. During the planet’s early days, the atmosphere was mostly made of carbon dioxide, methane and water vapor, instead of the nitrogen and oxygen that dominate today.

But around 2.45 billion years ago, the Great Oxidation Event occurred, during which the amount of oxygen in the atmosphere rose suddenly. The first oxygen-producing cyanobacteria are thought to have evolved two to three billion years ago. Scientists understood this through other lines of evidence, such as geochemical signatures, but before this week’s study, the earliest fossils of cyanobacteria with thylakoids were only around 500 million years old.

For the new study, researchers looked at cyanobacteria fossils from Australia, the Democratic Republic of the Congo and the Canadian Arctic. They sliced the fossils into slivers much thinner than a sheet of paper and studied their makeup with an electron microscope. Observing the arrangement of structures in the cells was “unambiguous,” Javaux tells Gizmodo—it resembled the hardware for photosynthesis.

Scientists found evidence of thylakoids in the Australian fossils, which date to between 1.73 and 1.78 billion years ago, as well as the Canadian fossils, which are 900 million to 1.01 billion years old. The fossils from the Democratic Republic of the Congo, which were about one billion years old, did not have signs of thylakoid membranes, per Ars Technica’s John Timmer.

“This is the kind of information that I thought we were not going to be able to pull out of fossils,” Woodward Fischer, a geobiologist at Caltech who did not contribute to the findings, tells Science News.

The paper shows the importance of studying the fossil record to determine the early evolution of cyanobacteria, per the study. Researchers are still trying to determine when cyanobacteria with thylakoid membranes split evolutionarily from those without—it is thought to have occurred between 2 billion and 2.7 billion years ago.

“If we are interested in the early version of our planet and life, these cyanobacteria are very important microorganisms, because they are the one who invented this oxygenic photosynthesis,” Javaux tells Courthouse News’ Hillel Aron. “This changed, completely, the chemistry of Earth over the years.”

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.