(ORDO NEWS) — The incredible discovery provided a new source for understanding life on ancient Earth.
A team of geologists have discovered tiny remnants of prokaryotic and algal life trapped inside halite crystals that formed 830 million years ago.
Halite is sodium chloride, also known as rock salt, and this discovery suggests that this naturally occurring mineral may be a previously untapped resource for studying ancient salty water environments.
What’s more, the organisms trapped in it may still be alive.
This unusual study also has implications for the search for ancient life not only on Earth, but also in extraterrestrial environments such as Mars, where large salt deposits have been identified as evidence of ancient large-scale reservoirs of liquid water.
Organisms don’t look the way you’d expect. Previous ancient microfossils have been found embedded in rocks such as shale that are billions of years old. Salt is not able to preserve organic materials in the same way.
Instead, when crystals form in a salty environment, there may be a small amount of liquid inside them. Such inclusions are called fluid inclusions, and they are the remains of parental waters from which halite crystallized.
This makes them valuable from a scientific point of view, since they can contain information about the temperature of the water, the chemical composition of the water, and even the temperature of the atmosphere at the time the mineral was formed.
Scientists have also found microorganisms living in recent and modern environments where halite forms. These environments are extremely salty; however, micro-organisms such as bacteria, fungi and algae thrive in them.
In addition, microorganisms have been found in liquid inclusions in gypsum and halite, mostly modern or recent, with some dating back to ancient times. However, the method of identifying these ancient organisms leaves doubt that they are of the same age as the halite.
“Therefore, a question remains among geomicrobiologists,” writes a group led by geologist Sarah Schroeder-Gomez of West Virginia University. “What are the oldest chemical sedimentary rocks containing prokaryotic and eukaryotic microorganisms from the sediment environment?”.
Now the middle part of Australia is a desert, but once it was an ancient salty sea. The Brown Formation is a well-studied and dated Neoproterozoic stratigraphic unit from central Australia. It includes extensive halite, evidence of an ancient marine environment.
Using a core sample from the Brown Formation recovered by the Western Australian Geological Survey in 1997, Schroeder-Gomez and her colleagues were able to study unaltered Neoproterozoic halite using only non-invasive optical techniques.
As a result, the halite remained intact, which, importantly, means that everything that was inside must have been locked up at the moment the crystals formed.
They used transmitted light and ultraviolet petrography, first at low magnification to identify halite crystals, and then at up to 2,000 times magnification to study the fluid inclusions they contained.
Inside, they found organic solids and liquids consistent with prokaryotic and eukaryotic cells, judging by their size, shape, and ultraviolet fluorescence.
The range of fluorescence was also interesting. Some samples showed a color consistent with organic decay, while others showed fluorescence characteristic of modern organisms, which the researchers say is indicative of unaltered organic material.
It is even possible that some organisms are still alive, the researchers noted. Liquid inclusions can serve as microhabitats where tiny colonies thrive. Living prokaryotes have been extracted from 250 million year old halite, why not extract them from 830 million?
“The feasibility of microbial survival on geologic time scales is not fully understood,” the researchers write.
“Radiation is expected to degrade organic matter over long periods of time, but Nicastro et al. (2002) found that a 250-million-year-old buried halite was only marginally exposed to radiation.
In addition, microorganisms can survive in liquid inclusions through metabolic changes , including starvation and cyst stages, as well as coexistence with organic compounds or dead cells that can serve as sources of nutrients.”
This certainly matters on Mars, where deposits similar in composition to the Brown Formation can be found, the researchers say. Their study shows how such organisms can be identified without destroying or damaging the samples, which could give us a new set of tools for identifying them – and better understanding Earth’s history.
“Optical exploration should be seen as a fundamental step in any study of biosignatures in ancient rocks. It allows the geological context of microorganisms to be known before further chemical or biological analyzes are carried out … and provides a target for such analyses,” the team writes.
“Ancient chemical deposits, both terrestrial and extraterrestrial, should be considered as potential hosts for ancient microorganisms and organic compounds.”
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