Millions of years old organisms found trapped in ancient rock
An amazing discovery has just been made about a potential new source for understanding life on ancient Earth.
And a team of geologists discovered tiny remains of prokaryotic life and algae - trapped inside halite crystals dating back 830 million years.
Halite is known as sodium chloride, also known as rock salt, and the discovery indicates that this natural mineral could be a previously untapped resource for the study of ancient saltwater environments.
Furthermore, the organisms trapped in it might still be alive.
Ancient microfossils are found compacted in rock formations, such as shale, that are billions of years old. Salt is not able to preserve organic matter in the same way.
Alternatively, when crystals form in the saltwater environment, small amounts of liquid can be trapped inside. These are called inclusions of liquids, and are the remains of the mother water from which the halite crystallized.
This makes them scientifically valuable, because they can contain information about the temperature of the water, the chemistry of the water, and even the temperature of the atmosphere at the time the mineral was formed.
Scientists also found microorganisms living in the modern environments where halite is formed. These are hypersaline environments, however, and microorganisms such as bacteria, fungi, and algae have been found thriving in them.
In addition, microorganisms have been documented in fluid inclusions in gypsum and halite, mostly recent, with a handful dating back to ancient times. However, the method of identifying these ancient objects left some doubt as to whether they were the same age as the halite.
"Therefore, there has been an open question among microbiologists," wrote a team led by geoscientist Sarah Schrader-Gomez of West Virginia University. What are the oldest chemical sedimentary rocks containing prokaryotic and eukaryotic microorganisms from a sedimentary environment?
Central Australia is now known as desert, but it was once an ancient salty sea. The Brown Formation is a well-characterized and dated stratigraphic unit from central Australia, dating back to the Cenozoic era. They include extensive halite, evidence of an ancient marine environment.
Using a core sample of the Brown Formation extracted by the Western Australian Geological Survey in 1997, Schrader-Gomez and colleagues were able to carry out investigations of unaltered Neproterozoic halite using non-invasive optical methods. This left the halite intact. Which means, importantly, that whatever's inside must have been trapped by the time the crystals formed.
They used ultraviolet and transmitted light rock imaging, first at low magnification to identify the halite crystals, and then up to 2,000-fold magnification to study the fluid inclusions in them.
Inside, they found organic solids and liquids, compatible with prokaryotic and eukaryotic cells, based on their size, shape and ultraviolet fluorescence.
The range of brilliance was also very interesting. Some samples showed colors consistent with organic decomposition, while others showed the same fluorescence as modern organisms, suggesting, the researchers said, unaltered organic matter.
The researchers pointed out that it is possible that some organisms are still alive. The fluid contents can serve as microhabitats where young colonies thrive. Living prokaryotes have been extracted from halite dating back 250 million years.
The researchers wrote: “The potential survival of microorganisms on geological time scales is not fully understood. It was suggested that radiation would destroy organic material over long periods of time, however it was found that buried 250-million-year-old halite was exposed to only trace amounts of radiation. In addition, microorganisms may live in fluids.”
This certainly has implications for Mars, the researchers said, where deposits with compositions similar to Brown's could be found. Their research shows how these organisms can be identified without destroying or disrupting samples, which could give us a new set of tools to identify them - and better understand Earth's history, too.
The team wrote: “Visual inspection should be considered an essential step in any study of biosignatures in ancient rocks. It allows knowledge of the geological context of microorganisms prior to further chemical or biological analyses, and provides a target for such analyses. Ancient chemical deposits, both terrestrial and of extraterrestrial origin, should be considered as potential hosts for ancient microorganisms and organic compounds.”
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