A surprising discovery has just revealed a possibility for a new way to experience life on ancient Earth.
A team of geologists has just discovered tiny remnants of prokaryotic and algal life trapped inside halite crystals dating back to 830 million years ago.
Halite is a sodium chloride, also known as rock salt, and the discovery suggests that this natural mineral might be a previously untapped resource for studying ancient saltwater environments.
En outre, the organisms that are trapped there may still be alive.
A large salt deposits have been identified as evidence of ancient, large-scale liquid water reservoirs, which has implications for the search for ancient life not just on Earth, but on other extraterrestrial environments.
Ancient microfossils have been discovered encased in rock structures, such as shale, dating back billions of years. Salt is not able to preserve organic material in the same way.
When crystals form in a saltwater environment, small amounts of fluid are trapped inside. These are known fluid inclusions, and they are remnants of the parent waters from which the halite crystals were crystallized.
These products are scientifically valuable, given that they may include information about the water temperature, water chemistry, and even the atmospheric temperature at the time the mineral formed.
Microorganisms have been found thriving in more recent and modern areas where halite forms. These environments are extremely salty, but numerous diseases have all been discovered.
Microorganisms have been found in fluid inclusions in gypsum and halite, mostly modern or recent, with a handful dating back to ancient times. However, the method of identifying these ancient organisms has left some doubt as to whether they are the same age as the halite.
"Therefore, a question has arisen among geomicrobiologists," says a research led by 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 a salty sea. The Browne Formation, which dates back to the Neoproterozoic, is a well-characterized and dated stratigraphic structure. It includes an extensive halite, which suggests an ancient marine environment.
Schreder-Gomes and her colleagues were able to conduct experiments of unaltered Neoproterozoic halite using only non-invasive optical methods. This allowed the halite to be intact, which is important because everything inside had to be trapped at the time the crystals formed.
They used sand-light and ultraviolet petrography, first at low magnification to identify halite crystals, then at up to 2,000x magnification to investigate the substances found therein.
Depending on their size, shape, and ultraviolet fluorescence, organic solids and liquids, compatible with prokaryotic and eukaryotic cells.
Despite the differences in fluorescence, some samples showed signs of organic decay, while others showed the same fluorescence of modern organisms, suggesting that organic material is unaltered.
Some of the organisms may be still alive, according to researchers. The fluid inclusions might serve as microhabitats where tiny colonies thrive. And living prokaryotes have been extracted from halite dating back 250 million years; why not 830 million?
"The potential for microorganisms to survive on geologic time scales is unknown," said the researchers.
"It has been suggested that radiation would destroy organic matter for long periods, yet Nicastro and al. (2002) discovered that buried 250 million-year-old halite was exposed to only negligible amounts of radiation. In addition, microorganisms may survive in fluid inclusions due to metabolic changes, including starvation survival and cyst stages, and coexistence with organic compounds or dead cells that might serve as nutrient sources."
The researchers said this situation has absolutely implications for Mars, where deposits can be found that have similar compositions to the Browne Formation. Using this information, they demonstrate how organisms can be identified without destroying or disrupting the samples, which might give us a new set of tools for identifying them and better understanding Earth''s history.
"Optical examination should be considered a fundamental step in any study of biosignaturesin ancient rocks. It allows geologic context of microorganisms to be known prior to further chemical or biological investigations, and it provides a target for such analyses," the team said.
"Ancient chemical sediments, both of terrestrial and extraterrestrial origin, should be considered as potential habitats for ancient microorganisms and organic compounds."
Geology has published these results.