In the scorching deserts of Namibia, Oman, and Saudi Arabia, scientists have discovered intriguing structures in marble and limestone. These microscopic tunnels, perfectly aligned, could be the work of a previously unknown form of microbial life.
This discovery, published in the journal
Geomicrobiology Journal, opens new perspectives on life's ability to adapt to extreme environments. The researchers, led by Professor Cees Passchier from Johannes Gutenberg University in Mainz, identified these structures during fieldwork in Namibia. These tunnels, several million years old, could reveal unsuspected biological interactions between microbes and rocks.
A) Free specimen showing a high density of micro-burrows (upper half), partially filled with white deposits.
B) Two in situ bands of low-density micro-burrows filled with white material originating from a white layer.
C) Freshly cut surface showing a well-developed band and two less distinct bands of low-density micro-burrows originating from a white layer.
D) Free fragment with branched bands of low-density micro-burrows. Its lower surface is covered with an endostromatolite layer.
E) Bands of micro-burrows along fractures in black marble, Saudi Arabia.
F) Two bands of micro-burrows with different orientations but parallel micro-burrows in a freshly cut sample. Structures that challenge geological explanations
The discovered tunnels exhibit characteristics that clearly distinguish them from classic geological processes. With a diameter of less than half a millimeter (0.02 inches), these micro-tunnels extend several centimeters and form parallel bands up to ten meters (33 feet) long. Their precise organization and regularity suggest a biological origin, unlike random formations created by erosion or tectonic forces. These structures, first observed 15 years ago, have since been identified in several desert regions, indicating a widespread phenomenon.
Inside these tunnels, scientists have identified a fine powder of calcium carbonate, likely a residue of microbial activity. This powder, composed mainly of calcite, indicates that microorganisms extracted nutrients from marble and limestone, leaving behind this finely ground material. Researchers hypothesize that these organisms used calcium carbonate as an energy source, a theory supported by traces of biological material in the samples. However, no direct evidence, such as DNA or proteins, has been extracted to confirm their identity.
These tunnels resemble no known geological formation. Their parallel alignment and banded distribution suggest organized activity, typical of a biological process. Scientists have also noted the presence of calcrete crusts around the tunnels, adding another layer of complexity to their formation. These unique features raise questions about the biological mechanisms at work and the nature of the responsible microorganisms.
A biological enigma millions of years old
The tunnels discovered in these rocks date back to a time when the climate of today's deserts was more humid, approximately one to two million years ago. Researchers estimate that these structures formed under conditions more favorable to microbial life, far different from the current aridity. However, the identity of the responsible microorganisms remains unknown, and no traces of DNA or proteins have been extracted from the samples. These tunnels, deeply embedded in the rock, suggest that these organisms survived without light in an extremely hostile environment.
The presence of biological material in the tunnels confirms the hypothesis of microbial activity, but scientists do not know whether it was an existing or extinct species. These organisms, capable of surviving without light, could belong to an as-yet-unrecorded microbial lineage. Their ability to interact with rocks and extract nutrients under extreme conditions makes them a subject of study for biologists and geologists. Researchers hope further analyses will identify the biological mechanisms behind these tunnels.
These discoveries could also shed light on our understanding of ancient ecosystems and their evolution. Scientists emphasize that these microorganisms may have played a role in transforming carbonate rocks, influencing the carbon cycle on a local or even global scale. Although their exact impact remains to be quantified, this work opens new perspectives on the interactions between microbial life and geological processes.
Article author: Cédric DEPOND