Oldest Fossils Just ‘an Illusion,’ Scientists Contend

One of the most heralded findings of paleontology--3.5-billion-year-old rocks considered to be the Earth’s oldest fossils--may be merely “an illusion,” according to a new analysis published Thursday.

The report, which claims the rocks do not contain any signs of life at all, is hotly contested by the fossils’ original discoverer. If true, however, it could rewrite much of Earth’s early history. It could also change notions of whether the planet’s first life evolved in warm pools or scalding hot springs. That, in turn, has bearing on how likely it is that life may have taken hold on other planets.

UCLA paleontologist J. William Schopf received worldwide acclaim a decade ago when he said he had discovered 3.5-billion-year-old fossils in ancient Australian rock. He concluded that some of the tiny traces were the remains of cyanobacteria capable of photosynthesis that lived in shallow, sunlit lagoons.

Because more conclusive fossils showing signs of life are just 2.7 billion years old, the older find suggested that relatively complex life forms had evolved on Earth spectacularly quickly--soon after the planet’s first rocks formed.

The appearance of cyanobacteria is a benchmark in Earth history. The organisms produce oxygen and were largely responsible for shaping the environment that made the evolution of air-breathing creatures, like ourselves, possible.

The arguments now swirling around the ancient rocks involve complex geochemical analyses and questions about what scientists see when they look through their microscopes.

Schopf sees complex biological structures that resemble bacteria that live today: filaments of barrel-shaped cells capped by distinct muffin-shaped cells on either end.

But a group of experts from England and Australia say that Schopf--and the many scientists who accepted his findings and enshrined them in textbooks--were fooled. Schopf’s fossils, they claim, are nothing more than exotic minerals, rock flaws and isolated bubbles and blobs.

“The cells are an illusion,” said Martin D. Brasier, a paleontologist at the University of Oxford who led the analysis published in today’s issue of the journal Nature.

As proof, he said some of the same structures described by Schopf have been found within volcanic glass, a place where life forms have never been detected. He described himself as “100% confident” in the new results.

Schopf is equally confident that Brasier’s team is wrong. When questions arose, Schopf reexamined his original rock samples using a new and superior imaging technique.

The new technique, he writes in a paper also published in today’s issue of Nature, offers the strongest evidence yet that the fossils have distinct shapes reminiscent of microbes. The shapes are made of a coal-like organic carbon that is a signature of living creatures, he said.

Brasier asserts that a rare chemical process, and not life forms, created the organic carbon. Schopf dismisses that as something that “has never, ever been identified in the geological record.”

“They’re just wrong. These are good fossils,” Schopf said.

The dispute demonstrates the difficulty of looking for the first traces of life on Earth. Few rocks from the Earth’s earliest epochs have survived unscathed. And the first life forms--microbes without bones or hard outer shells--don’t leave much of a trace.

The ancient fossil organisms are the most difficult he has ever worked with, microbes that are “fried, decayed, broken up,” Schopf said.

“When you say fossils, people think about dinosaurs and wonder why this is so difficult,” said Andrew Knoll, a Harvard University paleontologist and expert on younger and more complex bacterial fossils than those studied by Schopf. “It’s a really tough game to find evidence of life in these really, really old rocks.”

Knoll agrees Schopf’s rocks may contain chemical traces of some type of past life but has long questioned the assumption that the chemicals came from photosynthetic bacteria. There just isn’t enough evidence, Knoll said, to describe the physiological workings of ancient life forms.

David DesMarais at NASA Ames Research Center, an expert on the Earth’s early chemistry, said the new report raises questions about whether living things caused the microstructures seen in the rocks. DesMarais said he believes the distinct form of carbon in the rocks probably did come from living creatures.

It is unlikely that the carbon came from a rare chemical process, as Brasier asserts, DesMarais said.

The most important part of the new paper is what it adds to our ideas about how life formed, he added. A thorough geological analysis shows that the rocks did not come from a warm shallow pool but from a hydrothermal spring 150 feet below ground.

The finding adds weight to the theories that Earth’s first life may have originated in a tempestuous environment--on the flanks of undersea volcanic vents or in steaming hot springs like those now found in Yellowstone National Park.

Schopf, who heads the Center for the Study of Evolution and the Origin of Life at UCLA, is considered the “dean of ancient life” and a leader of the field he helped create.

He has spent much of his career debunking myriad false claims of fossils in ancient rock. In 1996, Schopf was one of the most vocal critics of an idea put forth by NASA scientists that a Martian meteorite contained traces of extraterrestrial microscopic life. The idea has since been discredited.

Now the same criticisms Schopf leveled at the Mars rock--that the signs were not biological at all--are being leveled against his own work.

Said Henry Gee, an editor at Nature who wrote an article accompanying the new research: “That is the name of the game for claims of life at the extremes of time and space.”