An abundance of fossils resembling seaweed uncovered in southern China may prove to be some of the oldest plants ever discovered. Previously the earliest uncovered evidence of creatures resembling what we would consider modern organisms was dated around 580 million years ago. The Chinese fossil discovery chronicled in the Feb. 16 issue of Nature puts this number back another 20 million to 56 million years.
Most researchers agree that creatures resembling moder physical forms didn’t evolve until around 635 million years ago as the Earth began thawing from a severe ice age that had much of the planet covered with glaciers. Of course with the earlier documented evidence dated to around 580 million years, that left a large 55 million year mysterious interval. The latest discovery fits nicely into that gap.
“It’s not the oldest multicellular life,” noted Virginia Tech paleontologist Shuhai Xiao, a co-author of the study. “But it is a collection of the oldest diverse, complex and macroscopic multicellular life.”
The research team discovered the bevy of fossils in a rocky outcrop in China’s southern Anhui Province. Decades earlier survey geologists found rich fossil beds located in a 260-foot-thick section of rock called the Lantian Formation but getting the age estimates proved rather tricky.
In an interested move to date these specimens, the team linked the Lantian layers of rock to corresponding, precisely dated formations hundreds of miles away. Through this method the fossils proved to be layered in sediment laid down between 580 million and 635 million years ago.
Xiao and the research team began excavating one site about a year ago unearthed more than 3,000 detailed specimens. “It was a very different world then than it is now, just algae and bacteria. Burrowing animals hadn’t evolved yet, so sediments on the bottom weren’t being churned up,” adds Xiao. “You get these beautiful fossils as a result.”
Most of the rust-colored specimens have splayed branches, sweeping fans and conical blooms resembling those of modern kelps with a small grouping resembling modern animals called bilaterians, with their symmetrical tubes and ribbons.
The fossil discovery and knowledge is still rather new and it is too early to draw concrete conclusions and Xiao said, “It’s almost impossible for us to shoehorn them into modern phyla. There are probably some animals, but we’re just not sure,” Xiao added. “They don’t look like algae, yet we don’t see any modern animal analogs. They may be offshoots that died out.”
Despite the resemblance to modern oxygen creating plants this latest fossil evidence does not prove the oceans were the oygenated environment we are used to today. Paleobiologist Guy Narbonne of Queens University in Canada, who wasn’t involved in the study but added accompanying commentary to the article, figures the new fossils can help resolve the scientific riddles of ancient oxygen levels.
“We know the deep oceans became oxygenated about 500 million years ago, around the time of the Cambrian explosion. But with older oceans, we’re not as certain,” Narbonne said.
Large, multicellular life forms — even algae — need oxygen for survival and Narbonne notes, “Their story is entirely consistent with a shallow, sunbathed, oxygenated environment.”
Despite this observation, Narbonne goes on to share a slight problem with this theory. Geochemical tests of the Lantian rock indicate the algae lived in oxygen-free oceans. According to Xiao, the tests were done on rock layers about 20 in. apart. This distance in the sediment does geologically represent millions of years in time and he would like to do more exact testing around every half-inch seeing if there is evidence of brief periods of oxygenation that could have supported algae and other complex life.
“But the really hard, really tedious work we now face is to systematically and carefully describe each of the thousands of specimens recovered from the site,” Xiao said. “That data is going to be the bread and butter of our scientific understanding.”
Images: Some of thousands of purported 600-million-year-old fossils recovered from the Lantian Formation in China’s southern Anhui Province. (Zhe Chen/Nature)