Did Land-Dwellers Emerge 65 Million Years Earlier Than Was Thought?

ananyo writes "A controversial paper published in Nature argues that enigmatic fossils regarded as ancient sea creatures were actually land-dwelling lichen. If true, that would suggest life on land began 65 million years earlier than researchers now estimate. The nature of fossils from the Ediacaran period, some 635 million–542 million years ago, has been fiercely debated by palaeontologists. But where others envisage Ediacaran sea beds crawling with archaic animals, Gregory Retallack, a geologist at the University of Oregon in Eugene, sees these sites in southern Australia as dry, terrestrial landscapes dotted with lichens. He proposes that rock in the Ediacara Member in South Australia — where palaeontologist Reginald Sprigg first discovered Ediacaran fossils in 1947 — represents ancient soils, and presents new geological data. Among other lines of evidence, Retallack argues that the rock's red colour and weathering pattern indicate that the deposits were formed in terrestrial — not marine — environments (abstract). Others strongly disagree."

Life on Land May Not Have Evolved From the Sea

[Hugh Pickens writes]

Conventional wisdom has it that complex life evolved in the sea and then crawled up onto land but NPR reports that a provocative new study published in Nature suggests that the earliest large life forms may have appeared on land long before the oceans filled with creatures [npr.org] that swam and crawled and burrowed in the mud. Paleontologists have found fossil evidence for a scattering of animals called Ediacarans that predate the Cambrian explosion about 530 million years ago when complex life suddenly burst forth and filled the seas with a panoply of life forms. Many scientists have assumed Ediacarans were predecessors of jellyfish, worms and other invertebrates [nature.com] but palaeontologist Greg Retallack has been building the case that Ediacarans weren't in fact animals, but actually more like fungi or lichens [wikipedia.org] and that Ediacarans weren't even living in the sea, as everyone has assumed. "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," says Retallack adding that his new theory lends credence to the idea that life actually evolved on land and then moved into the sea. Paul Knauth at Arizona State University has been pondering this same possibility. "I don't have any problem with early evolution being primarily on land," says Knauth. "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." Knauth says it could help explain why the Cambrian explosion appears to be so rapid [wikipedia.org]. It's possible these many life forms gradually evolved on the land and then made a quick dash to the sea. "That means that the Earth was not a barren land surface until about 500 million years ago, as a lot of people have speculated."