Tiny fossils that spent nearly two billion years trapped in pieces of ancient rock give us the first evidence yet of photosynthesis on Earth.
In the McDermott Formation in the desert of northern Australia, small structures are called Thylakoids It was discovered in what is believed to be a fossil Cyanobacteria It dates back to 1.75 billion years ago.
These structures are found within the cells of today's photosynthetic organisms and contain the pigment chlorophyll used to absorb light for photosynthesis.
This means that microfossils represent the oldest direct evidence of photosynthesis, giving us a new lower limit on the age of emergence of thylakoid-bearing cyanobacteria, and a new tool for understanding early Earth's ecosystems and how life emerged on our planet.
“Our study provides direct evidence for the existence of metabolically active cyanobacteria that perform anoxic photosynthesis.” writes a team led by microbiologist Catherine Demoulin From the University of Liège.
The results suggest that detailed analysis of other fossils could identify more similar structures, pinpointing the moment when photosynthetic structures were devoured and powered by the first forms of complex algal cells.
Photosynthesis, which uses sunlight to convert water and carbon dioxide into glucose and oxygen, may seem like something plants and algae are quietly doing to themselves out there, but it's the basis for the survival of almost all living things.
Not only do photosynthetic organisms form the basis of most food webs, their metabolic processes fill the atmosphere with the breathable oxygen that most of us need to survive.
We know that early in Earth's history, there wasn't much oxygen floating freely in the atmosphere and oceans. However, various lines of geochemical evidence reveal that oxygen levels suddenly rose About 2.4 billion years ago What is known as the great oxidation event. It is not clear why this is, but one possibility is the emergence of photosynthetic organisms.
The oldest undisputed microfossil evidence of cyanobacteria is an organism called Eoentophysalis belcherensiseven dated 2.018 billion years ago. But fossils are often difficult to interpret, and their internal structure does not always remain intact. Not all cyanobacteria contain thylakoid.
Demoulin and her colleagues used different high-resolution microscopic techniques to explore the external and internal structures of microfossils of a species known as Navifosa magenensisIt is believed to be cyanobacteria. Within the bodies of single-celled organisms from two fossil classes, they found thylakoid membranes.
These fossils were from the Grassy Bay Formation in Canada, and dated to up to 1.01 billion years ago; and the McDermott Formation, which dates back 1.75 billion years. This extends the fossil record of thylakoids back up to 1.2 billion years – and means that oxygenic photosynthesis must have evolved before then.
But what we don't know yet is whether they evolved over time to contribute to the great oxidation event. Only finding ancient fossils and carefully studying them can give us an answer to this pressing question.
“Discovery of thylakoids preserved within them n. Magensis Reported here provide direct evidence for a minimum age around 1.75 billion years ago for the difference between thylakoid-bearing bacteria and non-thylakoid-containing cyanobacteria. The researchers write.
“We anticipate that similar ultrastructural analyzes of well-preserved microfossils may expand the geological record of oxygenic photosynthetic organisms, the early anoxic ecosystems in which complex cells evolved.”
The research was published in nature.
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