What are some of the oldest unanswered questions

Researchers present evidence of life 3.5 billion years old

Sydney - One of the great unanswered questions in biology revolves around the origin of life itself: When did the first cells come into being on Earth and where could one still find evidence of this today? The big problem here is not only the tinyness and fragility of fossils that are billions of years old, but above all the great dynamics of the geology of the earth: The ongoing upheavals in the earth's crust have only left stones from the first hour in very few places.

Nonetheless, researchers in the past have succeeded in identifying suspicious traces in some of these eons-old rocks, such as Canada and Greenland. The oldest remains of biological activity could therefore be over 3.7 billion years old - but these microfossils are anything but undisputed in the professional world. There is no definitive evidence that the graphite granules, filaments and tubular structures that were discovered are really remnants of cellular origin.

Microfossils in the Dresser Formation

But that could have changed now: Scientists who re-analyzed rocks in Australia that are around 3.5 billion years old have now found evidence that the structures they contain are actually fossil microorganisms, or at least their legacies. The team around Austria-born Raphael Baumgartner from the University of New South Wales in Sydney examined the Dresser Formation in the Pilbara region in the west of the continent, which is one of the oldest preserved rocks on earth.

The rocks contain layered structures that could be so-called stromatolites. These are sediments that arise during the growth of microorganisms in bodies of water and can appear in various forms. Admittedly, there has so far been no agreement as to whether the finds in the Dresser Formation are real stromatolites. Many scientists consider a formation of these structures without biological intervention to be more likely.

Characteristic structures

To clarify this question, Baumgartner and his colleagues drilled the rocks again in order to get to the best-preserved areas of the corresponding layers. In-depth analyzes of these new samples, which are enclosed in pyrite crystals using various methods, leave no doubt in the opinion of the scientists: "We found exceptionally well-preserved organic matter," says Baumgartner. These include thread-like structures that arise when biofilms are formed. According to the study presented in the journal "Geology", chemical investigations based on several methods also indicate that the recovered matter comes from living organisms.

Older than anything known before

"We are holding irrefutable proof of one of the oldest traces of life in the history of the earth," said Baumgartner. "No other find that is clearly considered a microbial residue is older than ours."

Since the microfossils are in such an extraordinarily good condition, the associated pyrite crystals should, in the opinion of the researchers, have been formed in a very short time. Some modern microorganisms break down sulfur and produce pyrite in the process - this could also apply to the microbes of the Dresser formation, the scientists speculate. If the earliest cells used sulfur as an energy source, pyrite could even have played a crucial role in the origin of life itself. (tberg, September 26th, 2019)