Researchers have uncovered the oldest known evidence of photosynthesis in ancient microfossils dating back 1.75 billion years. The findings provide remarkable new insights into how one of life’s most important biological processes first evolved on Earth.
Ancient Structures Reveal Origins of Oxygen-Producing Photosynthesis
The microfossils were discovered in Western Australia and contain well-preserved structures that are clear evidence of oxygen-producing photosynthesis during the Paleoproterozoic Era, according to a study published January 4th in the journal Nature.
Photosynthesis is the process plants and some bacteria use to convert sunlight into energy and oxygen. Scientists think oxygenic photosynthesis first evolved in ancient cyanobacteria, but when this happened has been unclear.
The newly analyzed fossils contain elongated sack-like features called thylakoids that are found today in cyanobacteria to house the photosynthetic machinery that converts CO2 into oxygen and biomass. Finding these thylakoids in such ancient fossils strongly suggests oxygenic photosynthesis had already evolved by that time.
“These fossils represent the oldest unambiguous evidence for the precise morphological structures that perform oxygenic photosynthesis,” said lead researcher Dr. Bill Schopf of the University of California, Los Angeles.
Discovery Provides New Clues to Origins of Life’s Breath
The findings help rewrite our understanding of when photosynthesis first started pumping oxygen into Earth’s atmosphere – a pivotal moment in evolutionary history that paved the way for more complex life.
“This narrows down the time window for the origin of oxygenic photosynthesis on Earth,” said Schopf. Earlier controversial evidence had suggested it emerged as early as 3 billion years ago.
The fossils also contain tell-tale chemical biomarkers of photosynthesis. By revealing structures capable of doing oxygenic photosynthesis were already present 1.75 billion years ago, the discovery suggests this critical biological function evolved much earlier than thought during the early stages of life on Earth.
“The ability to produce oxygen via photosynthesis was a seminal event in Earth’s history,” said geobiologist David Flannery. “Once oxygen was plentiful in the atmosphere and ocean, the stage was set for complex cellular life like algae and, eventually, for organisms like us.”
|Age of fossils
|1.75 billion years old
Controversy Over Earliest Traces of Photosynthesis Settled
The new findings help settle a longstanding debate over controversial 3.5 billion-year-old rock formations, also found in Western Australia, that some scientists argued represent the oldest signs of microbial life on Earth.
Schopf was first author on a 1993 paper that made that claim. But the discovery was later hotly contested, as some experts argued the rock features are non-biological mineral artifacts and do not indicate ancient life at all.
The new microfossils described in Schopf’s latest study put that controversy firmly to rest. They contain definitive biological structures and organic matter consistent with cyanobacteria that conduct oxygenic photosynthesis.
“An extraordinary claim requires extraordinary evidence,” said Harvard paleobiologist Andrew Knoll, who was not involved with the study. “This discovery ends the debate decisively. We can now say with confidence when this transformative metabolism arose on Earth.”
Revolutionary Findings Redefine Our Planet’s Early Chapters
The fossils reshape our narrative of when Earth transitioned from containing only single-celled lifeforms to more complex multicellular organisms.
“These microbes totally revolutionized the planet,” said evolutionary biologist Betul Kaçar at the University of Arizona, who wrote an analysis for Nature on the discovery’s broad impacts across multiple fields. “They filled the atmosphere with oxygen and basically enabled the evolution of all complex life that followed, including humans.”
With more oxygen available from photosynthesis, eukaryotes – cells with nuclei that make up plants, fungi and animals – first emerged around 1.25 billion years ago and diversified over time.
The researchers also found nitrogen isotopes within pigments left behind in the fossils, indicating the cyanobacteria had capabilities beyond just oxygenic photosynthesis. They likely also had nitrogen-fixing metabolism to convert nitrogen gas into useful cellular compounds.
“The capabilities of these primeval organisms were more sophisticated than had been anticipated,” said biogeochemist Woodward Fischer at the California Institute of Technology. “They were exerting remarkable influence over Earth’s early biosphere and environments much earlier than realized.”
Ancient Microbes Set Stage for Life as We Know It
Further research can help clarify how and why oxygenic photosynthesis ultimately emerged. But the fossils make clear this innovation was made very early by ancient bacteria – and the rest was evolutionary history.
“Photosynthesis was a prerequisite for virtually all higher life on Earth,” said evolutionary biologist Sir Julien Lorance from Oxford University. “It led to a cascade of radical changes – primeval microbes filling the air with oxygen, the expansion of algae in the oceans, then the movement of life onto land.”
While the descendants of these ancient cyanobacteria still conduct key parts of photosynthesis today across various ecosystems, the new findings redefine just how far back in time the story goes – shedding light on life’s first tiny steps out of the darkness through harnessing light from a young Sun.
“It is truly wondrous to uncover direct glimpses into that formative period in our planet’s very distant past,” said Schopf. “Photosynthesis utterly transformed Earth’s fate. And remarkably ancient bacteria had already evolved specialized structures to set that miraculous chain of events in motion long, long ago.”
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