An incredible discovery has just revealed a potential new source for understanding life on ancient Earth.
A team of geologists has just discovered tiny remains of prokaryotic and algal life – trapped inside halite crystals dating back to 830 million years ago.
Halite is sodium chloride, also known as rock salt, and the discovery suggests this naturally occurring mineral could be a previously untapped resource for studying ancient saltwater environments.
In addition, the organisms trapped there may still be alive.
The extraordinary study also has implications for the search for ancient life, not just on Earth, but in extraterrestrial environments, such as Marchor large salt deposits have been identified as evidence of ancient large-scale liquid water reservoirs.
The organisms don’t look like you expected. Earlier ancient microfossils have been found pressed into rock formations, such as shale, dating back billions of years. Salt is not able to retain organic matter in the same way.
Instead, when crystals form in a saltwater environment, small amounts of liquid can become trapped inside. These are called fluid inclusionsand these are remnants of the mother waters from which halite crystallized.
Scientists have also found microorganisms living in recent and modern environments where halite forms. These environments are extremely salty; however, microorganisms such as bacteriamushrooms and algae were all found thriving in them.
Additionally, microorganisms have been documented in fluid inclusions in gypsum and halite, mostly modern or recent, with a handful dating back to antiquity. However, the method of identifying these ancient organisms has left some doubt as to whether they are the same age as halite.
“Therefore, a question persists among geomicrobiologists,” write a team led by geologist Sara Schreder-Gomes of West Virginia University. “What are the oldest chemical sedimentary rocks that contain prokaryotic and eukaryotic microorganisms from the depositional environment?”
The middle of Australia is now desert, but it was once an ancient salt sea. the Browne’s formation is a well-characterized and dated stratigraphic unit of central Australia, dating to the Neoproterozoic. It includes extensive halite, indicative of an ancient marine environment.
Using a core sample from the Browne Formation excavated by the Geological Survey of Western Australia in 1997, Schreder-Gomes and colleagues were able to investigate unweathered Neoproterozoic halite using only optical methods. non-invasive. This left the halite intact; which, more importantly, means that whatever was inside must have been trapped when the crystals formed.
They used transmitted and ultraviolet light petrography, first at low magnification to identify halite crystals, then at up to 2,000x magnification to study the fluid inclusions they contain.
Inside, they found organic solids and liquids, consistent with prokaryotic and eukaryotic cells, based on their size, shape, and ultraviolet fluorescence.
The fluorescence range was also interesting. Some of the samples showed colors consistent with organic decomposition, while others exhibited the same fluorescence of modern organisms, suggesting, the researchers say, unweathered organic matter.
It’s even possible that some of the organisms are still alive, the researchers noted. Fluid inclusions could serve as microhabitats where tiny colonies thrive. And living prokaryotes have been extracted from sea rock dating back 250 million years; why not 830 million?
“The possible survival of microorganisms on geological time scales is not fully understood”, the researchers wrote.
“It has been suggested that radiation will destroy organic matter over long periods of time, but Nicastro et al. (2002) found that a 250-million-year-old buried halite was only exposed to negligible amounts of radiation. Additionally, microorganisms can survive in fluid inclusions through metabolic changes, including starvation survival and cyst stages, and coexistence with organic compounds or dead cells that could serve as nutrient sources. »
This absolutely has implications for Mars, where deposits that have compositions similar to the Browne Formation can be found, the researchers said. Their research shows how such organisms can be identified without destroying or disturbing the samples, which could give us a new set of tools to identify them – and better understand Earth’s history, too.
“Optical examination should be considered a fundamental step in any study of biosignatures in ancient rocks. It provides knowledge of the geological background of microorganisms before other chemical or biological analyses…and it provides a target for such analyzes”, the team wrote.
“Ancient chemical sediments, both of terrestrial and extraterrestrial origin, should be considered as potential hosts for ancient microorganisms and organic compounds.”
The research has been published in Geology.
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