In the desert areas of Namibia, Oman, and Saudi Arabia, researchers discovered tube-like structures likely the result of some boring or burrow activity by an unknown life form.
Study first author Professor Cees Passchier from Johannes Gutenberg University Mainz first noted the structures during geological field work in Namibia 15 years ago.
“We look at the structure of the rocks to find out how continents came together to form the supercontinent Gondwana 500 to 600 million years ago,” explains Passchier. “At that time, carbonate deposits formed in the ancient oceans and turned into marble due to pressure and heat.”
On the surface of some rocks he noted tiny tubes, about half a millimeter wide and up to three centimeters deep, lined up parallel to one another and forming bands up to ten meters long. The holes were not empty but filled with a fine powder of clean calcium carbonate, the same mineral forming the marble.
Passchier also found very similar structures during field work in Oman and in Saudi Arabia. They do not match structures formed by weathering or other geological processes.
The presence of mineral deposits covering some of the holes suggest they are quite old.
“Perhaps one or two million years,” says Passchier. “We assume that they were formed in a slightly more humid climate, not in the dry desert climate that prevails today.”
The structures resemble holes and burrows made by some organisms like bacteria, algae and lichens. The researchers found biological material, but no DNA or proteins that could provide further insights.
So-called endolithic microorganisms are not uncommon in desert areas as they can obtain their energy and nutrients from the rocks they live in. The rocks provide also shelter from the sun and harsh environment. In most cases the burrows are located just a few millimeters beneath the rock’s surface, but the structures from Namibia are unusually deep.
“We don’t currently know whether this is a life form that has become extinct or is still alive somewhere,” concludes Passchier. He hopes that specialists on endolithic organisms will look into this phenomenon in the future.
The study, “Subfossil Fracture-Related Euendolithic Micro-burrows in Marble and Limestone,” was published in the Geomicrobiology Journal.
Additional material and interviews provided by the Johannes Gutenberg University Mainz.