(ORDO NEWS) — Scientists from the UK have proven that the rocks found in Australia and dated almost 3.5 billion years old are the fossilized remains of bacterial mats, traces of the earliest life.
In South Africa and western Australia, only old rocks come to the surface, which may have been part of the platform of our planet’s first supercontinent.
The age of some parts of the Australian Pilbara craton reaches 3.6 billion years.
There are also rocks that are very reminiscent of the remains of bacterial mats – primitive biocenoses formed by films of microbes. Such formations are called stromatolites.
Unfortunately, the exact proof of the biogenic nature of such ancient specimens is an extremely difficult task.
There is no direct evidence of life left in them, and scientists have to rely on “circumstantial evidence” such as the content of various carbon isotopes or structural features.
Therefore, the age of the oldest reliably determined stromatolites is estimated at 3.43 billion years, although life itself appeared hundreds of millions of years earlier than this date.
The new work of British paleontologists connects with the activity of the oldest microbial rocks 3.48 billion years old, obtained in the same Pilbara craton. Article by Kyron Hickman-Lewis (Keyron Hickman-Lewis) and colleagues published in the journal Geology.
“When archaeologists find the foundations of a ruined city, they know it was built by humans because it retains evidence of such construction: doorways, roads, bricks,” says Hickman-Lewis.
“Likewise, stromatolites have characteristic structural elements that allow us to identify their formation processes and origin.”
The scientists examined the samples using a range of methods, including optical and Raman microscopy, scanning electron microscopy, mass spectrometry, computed tomography and synchrotron tomography.
Traces of microorganisms or organics were not found, however, many details of the microstructure of the rock indicated its connection with ancient life.
In particular, this is evidenced by the presence of many tiny “domes”, like an egg container. Scientists attribute their appearance to the photosynthetic activity of the microbes of the ancient bacterial mat: as the sediment covered the surface of the biofilm, they stretched upward, closer to the light.
Columnar (palisade) structures also indicate a biogenic origin. They are associated with the accumulation of minerals along microbial cells and are characteristic of modern stromatolites.
All this allows the authors of the work to confidently speak about the biogenic nature of the stromatolites of the Pilbara craton, which are the oldest evidence of life on Earth so far.
However, it is possible that more careful studies will allow us to refute these conclusions. One can recall how ancient stromatolites found in Greenland in 2016 later turned out to be simple rock, albeit heavily deformed.
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