Home Science and Nature Photosynthesis Evolved as Early as 1.75 Billion Years Ago, Microfossils Suggest

Photosynthesis Evolved as Early as 1.75 Billion Years Ago, Microfossils Suggest

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The earliest known evidence of photosynthetic structures has been identified inside a collection of the enigmatic cylindrical microfossils Navifusa majensis from the 1.75-billion-year-old McDermott Formation in Australia.

Navifusa majensis microfossils: (a) Navifusa majensis from the McDermott Formation, Tawallah Supergroup, northern Australia; (b) Navifusa majensis from the Grassy Bay Formation, Shaler Supergroup, Arctic Canada; (c) Navifusa majensis from the BIIc6 Formation, Mbuji-Mayi Supergroup, DRC. Scale bars – 50 µm. Image credit: Demoulin et al., doi: 10.1038/s41586-023-06896-7.

Oxygenic photosynthesis, in which sunlight catalyses the conversion of water and carbon dioxide into glucose and oxygen, is unique to cyanobacteria and related organelles within eukaryotes.

Cyanobacteria had an important role in the evolution of early life and were active during the Great Oxidation Event around 2.4 billion years ago, but the timings of the origins of oxygenic photosynthesis are debated owing to limited evidence.

“Today oxygenic photosynthesis is unique to cyanobacteria and their plastid relatives within eukaryotes,” said University of Liège paleontologist Catherine Demoulin and her colleagues.

“Although its origin before the Great Oxidation Event is still debated, the accumulation of oxygen profoundly modified the redox chemistry of the Earth and the evolution of the biosphere, including complex life.”

“Understanding the diversification of cyanobacteria is thus crucial to grasping the coevolution of our planet and life, but their early fossil record remains ambiguous.”

In their study, Demoulin and co-authors found the fossilized photosynthetic structures in the Navifusa majensis microfossils.

The microstructures are thylakoids — membrane-bound structures found inside the chloroplasts of plants and some modern cyanobacteria.

The researchers identified them in fossils from three different locations, but the oldest, which come from the McDermott Formation in Australia, are 1.75 billion years old (Paleoproterozoic Era).

Navifusa majensis is presumed to be a cyanobacterium. The discovery of thylakoids in a specimen of this age suggests that photosynthesis may have evolved at some point before 1.75 billion years ago.

It does not, however, solve the mystery of whether photosynthesis evolved before or after the Great Oxidation Event.

Similar ultrastructural analyses of older microfossils could help to answer this question and to determine whether the evolution of thylakoids contributed to the rise in oxygen levels at the time of the Great Oxidation Event.

“The discovery extends the thylakoid fossil record by at least 1.2  billion years and provides a minimum age for the divergence of thylakoid-bearing cyanobacteria at roughly 1.75  billion years ago,” the authors said.

“It allows the unambiguous identification of early oxygenic photosynthesizers and a new redox proxy for probing early Earth ecosystems, highlighting the importance of examining the ultrastructure of fossil cells to decipher their paleobiology and early evolution.”

The team’s paper was published today in the journal Nature.

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C.F. Demoulin et al. Oldest thylakoids in fossil cells directly evidence oxygenic photosynthesis. Nature, published online January 3, 2024; doi: 10.1038/s41586-023-06896-7

Source : Breaking Science News

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