Ocean source of Earth life questioned

EUGENE, Ore., Dec. 13 (UPI) -- The long-held assumption that complex life on Earth evolved in the sea then crawled onto land may be exactly backwards, a University of Oregon researcher says.

Paleontologist Greg Retallack says he believes the earliest large life forms may have appeared on land long before the oceans filled with creatures that swam and crawled and burrowed in the mud, National Public Radio reported Wednesday.

Paleontologists have found fossil evidence for mysterious organisms called Ediacarans that predate the period about 530 million years ago when complex life suddenly burst forth and filled the seas with a wide range of life forms.

Many scientists have considered Ediacarans as marine creatures, predecessors of jellyfish, worms and other invertebrates.

Retallack, writing in the journal Nature, argues Ediacarans weren't living in the sea, and the ancient Australian rocks where they're found are ancient soil, not marine mud.

These early life forms were landlubbers, he said.

"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," he said.

Asked if that suggests life evolved on land and later moved into the ocean, he says, "Yes, in a nutshell."

Other scientists say they've had the same thoughts.

"I don't have any problem with early evolution being primarily on land," Paul Knauth in the School of Earth and Space Exploration at Arizona State University said. "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."