Martin Smith

Martin Smith



Martin Smith

Life oozed out of the seas onto land somewhere between 450 and 500 million years ago, but we have almost no fossils from this period on land. That may be about to change. A scientist in the UK believes he has identified the oldest terrestrial organism yet discovered after careful analysis of 440 million-year-old microfossils gathered in Scotland and Sweden in the 1980s.

Durham University Earth scientist Martin Smith suggests in a new paper published in the Botanical Journal of the Linnean Society that a few fossilized filaments discovered in Scotland and Sweden are actually part of a root-like system used by fungus to gather nutrients from soil. They were long known as "problematic" fossils because nobody was sure what they were nor where they fit into fungal evolution.

Smith identified the filaments as part of an ancient fungus called Tortotubus, which bears some resemblance to modern mushrooms—though we have no fossils that could prove that the fungus had fruiting bodies like mushrooms do.

Based on his analysis, Smith argues that the filaments of the Tortotubus are clearly a nutrient-delivery system for the organism. Scientists have long believed that fungi were among the first life forms on land, largely because they play a key role in the nitrogen cycle, pulling oxygen and nitrogen down into the ground to form soil. Once the naked rock and shales of early landmasses were enhanced by fungus, plant life could begin to grow there too, thriving on the nutrients left behind by the fungus' digestive process.

When life on Earth expands into new territory—such as land—it seems to require pioneer organisms like fungus to seed the environment with nutrients. Billions of years before Tortotubus extended its filaments into dry land, another simple organism paved the way for multicellular life in the ocean. The humble cyanobacteria, or blue-green algae, pumped the atmosphere full of oxygen when they evolved photosynthesis, using photons to split water molecules, and releasing free oxygen as a byproduct of this energy-generating process. Like cyanobacteria, Tortotubus was a pioneer in its environment.

In a release, Smith commented:

During the period when this organism existed, life was almost entirely restricted to the oceans: nothing more complex than simple mossy and lichen-like plants had yet evolved on the land. But before there could be flowering plants or trees, or the animals that depend on them, the processes of rot and soil formation needed to be established.

Though we have no fossils of other life on land during this period, the fungus needed to feed on other organisms to survive. Smith believes it was probably eating bacteria or algae, decomposing them, and pumping nitrates back into the soil as it pulled energy from its rotting meal.