For nearly a billion years, the silent, sprawling kingdoms that prepared Earth for complex life were not green, but fungal. New research fundamentally rewrites the timeline of life's colonization of land, revealing that fungi predated plants and were likely the critical architects of terrestrial ecosystems.
The study, led by an international team from the Okinawa Institute of Science and Technology (OIST) and collaborators in Europe and published in Nature Ecology & Evolution, challenges the traditional plant-centric view of how life came to land.
While the fossil record provides rough timelines for animals, plants, and algae, fungi have remained a mystery. Their soft, filamentous bodies decompose quickly, leaving a sparse fossil record. To overcome this, the research team turned to a "molecular clock" technique, calibrated with a novel source of information: rare horizontal gene transfers (HGTs).
"Horizontal gene transfer is like a gene jumping 'sideways' from one species to another," explains Professor Gergely J. Szöllősi, a senior author of the study from OIST. "These events act as powerful temporal clues. If a gene from lineage A jumped into lineage B, it establishes a clear rule: the ancestors of lineage A must be older than the descendants of lineage B."
By identifying 17 such gene-swap events, the team created a web of "older than/younger than" relationships to constrain and refine the fungal family tree.
The analysis points to a common ancestor of all living fungi dating back a staggering 1.4 to 0.9 billion years. This places the diversification of fungi firmly in a pre-plant world.
"Fungi run ecosystems—recycling nutrients, partnering with other organisms," says Dr. Lénárd L. Szánthó, co-first author of the study. "Pinning down their timeline shows fungi were diversifying long before plants, consistent with early partnerships with algae that likely helped pave the way for terrestrial ecosystems."
This revised timeline paints a new picture of early Earth. It suggests that for hundreds of millions of years, fungi and algae formed symbiotic communities on land. These pioneering duos would have played a crucial role in breaking down rocks, releasing nutrients, and creating the first primitive soils—a process known as weathering.
In this view, plants did not colonize a barren wasteland. Instead, they stepped onto a stage that had been meticulously prepared for them over eons by the ancient and pervasive activity of fungi. The reign of fungi, it appears, made the world green.