There is a new source for understanding life on ancient Earth.
A team of geologists has discovered tiny remnants of prokaryotic and algal life that were trapped inside crystals of halite.
Halite, also known as rock salt, is a natural mineral that could be used to study ancient saltwater environments.
The organisms may still be alive.
There are implications for the search for ancient life, not just on Earth, but in extraterrestrial environments, such as Mars, where large salt deposits have been identified as evidence of ancient, large-scale liquid water.
The organisms look different than you might expect. Microfossils have been found in rock formations dating back billions of years. Salt can't preserve organic material in the same way.
Small amounts of fluid can be trapped inside when the crystals are forming in a saltwater environment. These are remnants of the parent waters that the halite came from.
Information about the water temperature, water chemistry and even atmospheric temperature can be found in them.
Scientists have found organisms in recent and modern environments. The environments are very salty and have many organisms thriving in them.
Micro organisms have been documented in fluid inclusions in gypsum and halite, with a few dating back to ancient times. The method of identifying these ancient organisms left some doubt as to whether they are the same age as the halite.
A team led by Sara Schreder-Gomes of West Virginia University wrote a question about the oldest rocks.
The middle of Australia was once a salty sea. The Browne Formation is a well-characterized and dated unit from central Australia. It is indicative of an ancient marine environment.
In 1997 a core sample from the Browne Formation was taken by the Geological Survey of Western Australia and used to conduct investigations. This means that anything inside had to have been trapped at the time the crystals formed.
At low magnification, they used transmitted-light and ultraviolet petrography to identify halite crystals, then at up to 2,000x magnification to study the fluid inclusions therein.
They found organic liquids andsolids that were consistent with prokaryotic and eukaryotic cells.
It was interesting to see the range of fluorescence. The researchers said that some of the samples showed colors consistent with organic decay, while others showed the same fluorescence of modern organisms.
Some of the organisms may still be alive, according to the researchers. The fluid could be used as a base for colonies. Why not take living prokaryotes from halite, which has been around for 250 million years?
The researchers wrote that survival of microorganisms over geologic time scales is not fully understood.
It has been suggested that radiation would destroy organic matter over a long time period. Micro organisms can survive in fluid by metabolism changes, including starvation survival and cyst stages, as well as coexisting with organic compounds or dead cells.
The researchers said that this has implications for Mars, where similar deposits can be found. Their research shows how such organisms can be identified without destroying or disrupting the samples, which could give us a new set of tools for identifying them and better understanding Earth's own history.
Any study of biosignatures in ancient rocks should consider optical examination a fundamental step. The team wrote that it allows geologic context of microorganisms to be known prior to further analyses.
Potential hosts for ancient microorganisms and organic compounds can be found in the ancient chemical sediments.
The research has been published.
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