A team of geologists has discovered tiny remnants of prokaryotic and algal life trapped inside halite crystals dating back 830 million years. It is a discovery that will be considered very seriously in the scientific world.
Halite is sodium chloride, also known as rock salt, and the discovery shows that this natural mineral could be a previously untapped resource for studying ancient saltwater environments. What is more interesting is the probability that these organisms are still alive.
It reveals the importance of the extraordinary work to the life of large salt deposits, not only on Earth but also in extraterrestrial environments such as Mars.
This discovery will be a great addition to the ancient search for life studies of ancient, large-scale liquid water reservoirs. But the organisms don't appear as we expect them to.
Previous ancient microfossils have been found pressed into rock formations such as leafstone that date back billions of years.
Salt cannot preserve organic matter in the same way. In other words, the discovery brings with it new unknowns.
When crystals form in a saltwater environment, a small amount of liquid may be trapped inside. These are called fluid inclusions, and they are remnants of the mother waters from which halite crystallized. This makes them scientifically valuable because they can contain information about the water temperature at the time the mineral was formed, water chemistry, and even atmospheric temperature.
What is Halite Crystal?
Halite, commonly known as rock salt, is a type of salt that is the mineral (natural) form of sodium chloride (NaCl). Halite forms isometric crystals.
The mineral is typically colorless or white, but can also be light blue, dark blue, purple, pink, red, orange, yellow, or gray depending on the presence of other materials, impurities, and structural or isotopic abnormalities in the crystals. It usually occurs with other evaporite precipitate minerals such as sulfates, halides, and a few of the borates. The name Halite is derived from the Ancient Greek word ἅλς (háls), meaning "salt".
Halite occurs predominantly in sedimentary rocks formed by the evaporation of seawater or salty lake water. Large deposits of sedimentary evaporite mineral deposits, including halite, may result from the drying up of closed lakes and restricted seas. Such salt deposits can be hundreds of meters thick and may lie under large areas. Halite forms on the surface in playas in areas where evaporation exceeds precipitation, such as the salt flats of Badwater Basin in Death Valley National Park today.
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Scientists have also found microorganisms living in recent and modern environments where halite was formed. These environments are extremely salty; However, microorganisms such as bacteria, fungi, and algae have all been found to thrive.
Additionally, microorganisms have been documented in liquid inclusions in gypsum and halite, many of which are modern or new, and a handful of them date back to ancient times.
However, this method of identifying these ancient organisms has left some doubts as to whether they are the same age as halite.
"Therefore, a question arose among geomicrobiologists," adds a team led by West Virginia University geologist Sara Schreder-Gomes.
“What are the oldest chemical sedimentary rocks containing prokaryotic and eukaryotic microorganisms from the sedimentary environment?”
The middle of Australia is now desert, but it was once an ancient salty sea. The Browne Formation is a well-characterized and dated formation from central Australia to the Neoproterozoic period. stratigraphic is the unit. It contains large halite, indicative of an ancient marine environment.
Schreder-Gomes and colleagues investigated intact Neoproterozoic halite using non-invasive optical methods using a core sample from the Browne Formation taken by the Western Australian Geological Survey in 1997.
This preserved halite indicated that everything inside must have been trapped at the time the crystals were forming.
They used transmitted light and ultraviolet petrography, first at low magnification to identify the halite crystals, then at up to 2.000x magnification to examine the fluid inclusions therein.
Inside, they found organic solids and liquids compatible with prokaryotic and eukaryotic cells based on their size, shape, and ultraviolet fluorescence.
The fluorescence range was also interesting. According to the researchers, some of the samples showed colors compatible with organic decay, while others showed the same fluorescence of modern organisms, suggesting unchanged organic material.
It's even possible that some organisms are still alive, the researchers said.
Fluid inclusions can act as microhabitats for small colonies. And why not 830 million years? Living prokaryotes were obtained from halite dating back 250 million years.
"The possible survival of microbes on geological time scales is not fully known," the researchers wrote.
“Although it was believed that prolonged radiation exposure would destroy organic matter, Nicastro et al. (2002) discovered that the buried 250-million-year-old halite was exposed to only small amounts of radiation.
Also, bacteria in fluid inclusions can survive through metabolic changes such as starvation survival and cyst stages.
It can live by coexisting with organic molecules or dead cells that can serve as sources of nutrition.
According to the researchers, it Browne Formation It has direct implications for Mars, where deposits with similar compositions have been discovered. Their discovery shows how to identify such organisms without damaging or disturbing the materials; this could provide us with a new set of tools for identifying them – as well as a deeper understanding of Earth's own history.
“Any search for biosignatures in ancient rocks should begin with an optical examination,” the group said. It allows the geological context of microorganisms to be determined before additional chemical or biological analysis… It also serves as a target for such research,” he informs the scientific world.
"Ancient chemical deposits, both terrestrial and interplanetary, should be considered as potential homes for ancient microbes and organic molecules."