The first land life may have appeared far earlier than was previously thought — at least 2.2 billion years ago, instead of the 500 million years ago that was estimated before, according to new research from the University of Oregon. The evidence that backs up the existence of this 2.2 billion year old land life is quite good — actual fossils.
Until this discovery it had been the general consensus in the scientific community that ‘complex’ land life only first appeared sometime around 500 million years — and that the early landscapes of the Earth were essentially barren. But the new research shows otherwise — providing solid evidence that life on land appeared at least as early as 2.2 billion years ago, around half way back to the time when the planet is thought to have arisen.
The new evidence — fossils about the size of match heads and attached into bunches by threads in the surface of an ancient soil from South Africa — are somewhat alien looking to modern eyes. “They have been named Diskagma buttonii, meaning ‘disc-shaped fragments of Andy Button’.”
“They certainly were not plants or animals, but something rather more simple,” stated geologist Gregory J. Retallack of the University of Oregon, professor of geological sciences and co-director of paleontological collections at the UO’s Museum of Natural and Cultural History. “The fossils most resemble modern soil organisms called Geosiphon, a fungus with a central cavity filled with symbiotic cyanobacteria.”
“There is independent evidence for cyanobacteria, but not fungi, of the same geological age, and these new fossils set a new and earlier benchmark for the greening of the land,” he stated. “This gains added significance because fossil soils hosting the fossils have long been taken as evidence for a marked rise in the amount of oxygen in the atmosphere at about 2.4 billion to 2.2 billion years ago, widely called the Great Oxidation Event.”
The University of Oregon continues:
By modern standards, in which Earth’s air is now 21% oxygen, this early rise was modest, to about 5% oxygen, but it represented a rise from vanishingly low oxygen levels earlier in geological time.
Demonstrating that Diskagma are fossils, Retallack said, was a technical triumph because they were too big to be completely seen in a standard microscopic slide and within rock that was too dark to see through in slabs. The samples were imaged using powerful X-rays of a cyclotron, a particle accelerator, at the Lawrence Berkeley National Laboratory in California.
The images enabled a three-dimensional restoration of the fossils’ form: odd little hollow urn-shaped structures with a terminal cup and basal attachment tube.
In their conclusion, the researchers noted that their newly named fossil Diskagma is comparable in morphology and size to Thucomyces lichenoides, a fossil dating to 2.8 billion years ago and also found in South Africa, but its composition, including interior structure and trace elements, is significantly different.
“At last we have an idea of what life on land looked like in the Precambrian,” Retallack stated. “Perhaps with this search image in mind, we can find more and different kinds of fossils in ancient soils.”
There are actually a couple of living organisms that bear some similarities to diskagma — the slime mold Leocarpus fragilis as found in Oregon’s Three Sisters Wilderness; the lichen Cladonia ecmocyna gathered near Fishtrap Lake in Montana; and the fungus Geosiphon pyriformis from near Darmstadt, Germany.
According to the researchers, the new fossil is “a promising candidate for the oldest known eukaryote –an organism with cells that contain complex structures, including a nucleus, within membranes.”
The new findings will be published in the journal Precambrian Research.