It is probably bacteria or algae that became trapped in the minerals hundreds of millions of years ago.

That can be read in the magazine geology† The study revolves around rock salt, which originated about 830 million years ago and was found in the Browne Formation in central Australia. “The mineral rock salt forms when there is an abundance of sodium and chloride ions in a solution,” explains researcher Sara Schreder-Gomes. Scientias.nl from. “When there are too many ions in a solution and the point of saturation is reached, solid minerals are formed.” Those minerals have a crystal structure. Which means they consist of a regular pattern of particles: in this case sodium and chloride ions. “However, when the rock salt crystals grow quickly, imperfections can form in those crystals and some water can become trapped in the structure of the crystal.” Some of those trapped liquids also contain solids, such as microorganisms that lived in the water near where the rock salt crystal formed.”

Bacteria or algae

And that’s exactly what researchers found in rock salt recovered in Australia. “Based on their size, shape and color, we can classify the microorganisms as prokaryotes (bacteria and/or archaea) or eukaryotes (possibly algae or fungi),” said Schreder-Gomes.

Remarkable

It’s a remarkable find. “We were not very surprised to find microorganisms in the rock salt from the Browne Formation,” said the researcher. “But we were very excited about it. Previous studies have already found microorganisms in modern rock salt and in older rock salt, with an age of up to 250 million years. It is remarkable that we were able to find microorganisms in such ancient minerals and that they were so well preserved too!”

Because the micro-organisms must have been trapped in the rock salt when it was formed, they must certainly be as old as the minerals themselves. And those minerals originated 830 million years ago, the researchers write.

extremophiles

It is not possible to say with certainty what kind of micro-organisms are involved. It could be bacteria, but also algae or fungi. However, based on the environment in which the unfortunate micro-organisms lived millions of years ago, the researchers think they can say something more about the nature of the tiny organisms. For example, we have to bear in mind that the crystals in which the micro-organisms are trapped were formed in very salty water. And therefore it is quite possible that the micro-organisms that are now found in the crystals can be classified as extremophiles. These are organisms that live under extreme conditions. That is not certain, however; for example, the microbes could also have been deposited in the extremely salty water by the wind. In that case, they are not extremophiles, but ‘normal’ micro-organisms that happened to end up in an extreme environment.

Here you see liquids trapped in rock salt containing micro-organisms. Image: Sara Schreder-Gomes.

Empathize?

However it turned out, one thing is certain: the micro-organisms were never able to escape from the crystal structure and are still trapped in it – 830 million years later. It seems like a tragic story. But it is not yet certain that all spotted micro-organisms have also died in solitary confinement, says Schreder-Gomes. “It is possible – but not likely – that these organisms are still alive. Some halophilic (salt-loving) organisms that we know today have survival mechanisms that enable them to survive even in times when conditions are unfavorable (for example, when there are limited nutrients available). For example, they put their metabolism on the back burner. We do not yet fully understand how microorganisms – and in particular the microorganisms in very salty environments – can survive for so long. In previous studies, researchers have sometimes extracted bacteria from rock salt up to 250 million years old and then put them in culture. Future research could similarly examine life in the Browne Formation.”

Pending that follow-up study, it remains a mystery whether the microorganisms survived their millions of years of captivity. But even if they are all dead, it remains an intriguing find. Because what this teaches us is that micro-organisms in rock salt can be preserved well and recognisably for hundreds of millions of years in a row. And that offers opportunities. For example, in the search for extraterrestrial life on Mars. The planet today is dry and cold and not directly attractive to life as we know it, but that may have been different in the past; there is plenty of evidence that the planet used to be wet and warm. If at that time Mars also harbored microbial life (which may have become extinct by now), then minerals may be a good place to look for them. “Mars is home to a collection of minerals and rock formations very similar to what we see in the Browne Formation,” explains Schreder-Gomes. And those minerals can also be imperfect and contain water. And if that water in turn harbored micro-organisms, they can still be recognisably trapped in that crystal structure. “Potential biosignatures could be stored and detected if we could study the trapped water here on Earth.” And so the implications of the work of Schreder-Gomes and colleagues could extend far beyond Earth. “The age of the rocks (which were studied for the research, ed.) is also important,” emphasizes Schreder-Gomes. “Because it shows that traces of life here on Earth – and therefore hopefully also on Mars – can still be detected after hundreds of millions of years.”