A new study proposes that land-based life, as shown by this Ediacaran fossil, may not have evolved from ocean animals. (Photo : Wikimedia Commons)
According to a new study with potentially earth-shaking ramifications towards evolutionary theories, land creatures may not have made their way up from the ocean depths onto land.
Gregory Retallack, a geologist who works at the University of Oregon in Eugene, suggests in his latest study, published in the journal Nature, that the first land-based lifeforms may have been in existence roughly 65 million years earlier than when scientists believed they did.
The Ediacaran period, which concluded some 540 million years ago, saw an abundance of marine animal life. With the discovery of Ediacaran fossils in South Australia, most scientists believed that those animals were marine invertebrates and the earliest forms of sea life that began to evolve into land-based creatures.
However, Retallack wrote that those creatures weren't animals, but were instead "similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts, rather than marine animals, or protests."
Those observations were based on Retallack studying evidence of fossil soils in that region that varied in chemistry, grain size, and clay minerals, while a number of fossils showed structures that were similar to lichens found today.
"What I'm saying for the Ediacaran is that the big [life] forms were on land and life was actually quite a bit simpler in the ocean," Retallack told Cap Radio.
When asked if his new theory lent credence to the idea that life had actually evolved on land and then moved into the sea, he replied, ""Yes, in a nutshell."
Some scientists believe that Retallack is on the right track with this new idea.
"I don't have any problem with early evolution being primarily on land," Paul Knauth, a professor in the School of Earth and Space Exploration at Arizona State University, told Cap Radio. "I think you can make a pretty good argument for that, and that it came into the sea later. It's kind of a radical idea, but the fact is we don't know."
Others, however, were not quite convinced.
Guy Narbonne, a palaeobiologist at Queen's University in Kingston, Ontario, told Nature that the new paper only summarized Retallack's "long-standing views" on Ediacaran life.
"Most of us appreciated that Retallack's lichen hypothesis was innovative thinking and tested his ideas critically, but it quickly became clear that there are simpler explanations for the features Retallack had validly noted, and most of us moved on to more promising explanations," he said.
Dr Jim Gehling of the South Australian Museum told the Australian Broadcasting Corporation that he had no doubt that the South Australian fossils came from the ocean.
"[Ninenty-nine] percent of the people who have worked on these agree," he said.