West Virginia University researchers believe they have discovered living microorganisms in a halite sample dating back 830 million years, providing insight into past life and environments.
The findings were published in the scientific journal Geological Society of America. The scientists examined a sample from the 830-million-year-old Browne Formation of central Australia, which was drilled in 1997 by the Geological Survey of Western Australia. They examined ten halite beds and split the halite into 1 to 2 millimeter pieces with a razor blade.
The team used non-invasive optical methods to analyze neoproterozoic halite, which allowed the halite to remain intact during the study and eliminated the risk of contamination by modern organisms. They identified halite crystals and fluid inclusions, or water trapped as the halite crystals formed, using transmitted light petrography. They could also see what was inside the individual fluid inclusions, such as microorganisms like bacteria, algae, or fungi. Scientists believe that some of these 830-million-year-old microorganisms may still be alive.
The researchers used high magnification and both transmitted and UV-visible light to see what was inside individual fluid inclusions – microorganisms that lived near the crystal’s surface millions of years ago.
According to Sara Schreder-Gomes, the study’s lead researcher, they discovered prokaryotes, or bacteria or archaea, that appeared clear, white, or pale orange. They also discovered eukaryotic cells that appeared yellow, pale orange, pale brown, or clear, indicating that they were likely salt-loving algae or fungi.
According to Schreder-Gomes, some of the eukaryotic cells had a halo coating of organic compounds around them.
As halite grows from salty surface waters, fluid inclusions entrap the water, creating microenvironments or habitats for trapped microorganisms, according to the researchers. According to the researchers, the bacteria and salt-loving algae or fungi found inside the halite crystals were trapped when the crystals formed, making them 830 million years old.
The difficult part is determining whether the microorganisms are still alive and how they have survived this long.
When host waters become too salty, microorganisms found in halite shrink and significantly reduce biological activity, according to the researchers. Based on previous research, these algal cells may be revived during subsequent flooding events. Bacteria have also survived in halite fluid inclusions, they claim, implying that the microorganisms in the most recent sample are likely alive.
Taking things a step further, the researchers believe that ancient chemical sediments, both on and off the planet, may contain ancient microorganisms and organic compounds similar to those found in halite samples.
According to Schreder-Gomes, their work could benefit NASA researchers.
She cites the NASA Perseverance rover, which landed on Mars on February 18, 2021, and is collecting samples for a future return to Earth. The Browne Formation studied by her team contains mineral deposits similar to those found on Mars, such as halite and gypsum. According to her, microorganisms that may have existed in water on Mars in the past may be trapped inside halite.
Researchers must use similar non-destructive optical techniques to examine samples brought back to Earth to find out, she said.
According to Lidya Tarhan, an assistant professor in Yale University’s Department of Earth and Planetary Sciences, having such a “well-preserved window into microbial life from this time interval, and captured, essentially, straight from seawater in these droplets of water that are then incorporated into these in these rock salt crystals” is unusual. Part of the reason it’s so hard to say if they are alive or not is because the microorganisms are so small, she said. While scientists can observe larger organisms to determine whether they are still alive, it’s difficult to do with smaller ones.
According to Tarhan, based on the researchers’ work and the properties of the organic cells described, the majority of them are not alive and are even decaying.
However, she believes that some of the organisms are still alive and well, which she finds exciting.
“This is an incredible snapshot of life 830 million years ago,” she said. “We have this really incredible window into the kinds of organisms that were either transported to salty shoreline deposits and captured by these fluid inclusions, or (organisms) that were living in those super salty, hyper salty waters.”