Although scientists have yet to determine the exact period when life from the seas migrated to land, it is generally agreed upon that the transition began about 450 to 500 million years ago during the Paleozoic era.
To kick-start the evolutionary process, there had to be nutrients on land supporting the growth of complex life-forms.
One such nutrient is that of a fossilized Scottish fungus, which was unearthed by experts from the University of Cambridge. The fossil is estimated to be about 440 million years old, making it one of the oldest samples of fossilized fungi.
It doesn't stop there. The fossil is also the oldest sample of any terrestrial organism ever found. So far, only the oldest fossils of sea creatures have been examined.
A Pioneer Of Evolution
Dr. Martin Smith, lead author of the fungi study, said life was almost entirely restricted to oceans during the time that the fungus existed. The sea organisms included simple lichen-like and mossy plants which had yet to evolve on land at that time.
Before there were trees or flowering plants, Smith said the process of rot and soil formation had to be established. The 440 million-year-old Tortotubus fungus may be tiny, but it was crucial to this very process, allowing plants to flourish and tempting animals to drift to dry land.
Smith attempted to reconstruct the method of growth for two different fossils found in the 1980s. The fossils were originally thought to be different organisms, but Smith was able to show that the fossils actually represented one organism at different stages of development.
Smith found that Tortotubus has cord-like arms that spread out and a main structure. Its arms may have allowed it to colonize surface, he said.
Samples of this fungus were found on the Scottish Inner Hebridean Island of Kerrera in Sweden, and they were shorter than the width of human hair.
Early fungi such as the Tortotubus began the rot and soil formation process by getting nitrogen and oxygen into the soil. When the fungi decompose, they convert compounds with nitrogen from animal and plant waste back into nitrates. These are added into the soil and received again by plants.
Fungi that are similar to Tortotubus are still alive today. They are very helpful in the decomposition of matter, moving nutrients around the soil and placing them where they are most useful.
But What Was There To Decompose?
Smith said that the fossil provides scientists a glimpse into complex fungal "behavior" in some of the earliest terrestrial ecosystems.
However, one particular question that struck the findings was this: what was there to decompose?
"It's likely that there were bacteria or algae on land during this period, but these organisms are rarely found as fossils," said Dr. Smith.
The fungus may have also been able to form mushrooms, Smith said, because it follows a similar pattern to modern organisms. With that, the fossil also gives scientists a clue that mushroom-forming fungi may have remained on land before animals migrated from the oceans.
"It fills an important gap in the evolution of life on land," added Smith.
The findings of the study are featured in the Botanical Journal of the Royal Linnean Society. It was supported by Clare College, Cambridge.
