New Analysis Throws Age of Life on Earth Into Doubt

Ben Harder
for National Geographic News

May 23, 2002

The most ancient organisms on Earth don't need Botox to make themselves appear suddenly younger. They might just need a good dose of revisionist geological science.

A fresh reading of the geology and geochemistry of an isolated corner of Greenland could shave at least 50 million years off the presumed age of the first living thing on the planet.

Past analysis of rocks found on Akilia, the remote island off the southwestern coast of Greenland, led scientists to conclude that they were at least 3.85 billion years old and contained evidence of the earliest life on the planet.

Not so, say Chris Fedo, a geologist at George Washington University in Washington, D.C., and Martin Whitehouse, a geologist at the Swedish Museum of Natural History in Stockholm. Having reexamined the rocks, they have reached two startling conclusions: The deposits aren't as old as had been believed, and they might not contain the remnants of living things at all.

The new interpretation is bound to face a fiery crucible as its merits are debated by scientists. Already, it has been challenged by Steve Mojzsis, a geologist at the University of Colorado–Boulder, who previously analyzed the Akilia rocks and champions the alternative theory.

Life on the Rocks?

One patch of rock on Akilia is striped with alternating bands of green and white. Mojzsis concluded that sediments deposited on the bottom of an ocean at least 3.85 billion years old formed the banded rocks. "That would [make] them the oldest known sediments on the Earth," he says.

Because sediments accumulate underwater, Mojzsis's interpretation implies that the rocks formed at a time when watery environments—believed to have been the setting for life's evolution—existed. Sedimentary rock forms gradually, as material in water drifts down, settles on the ocean floor, and eventually hardens into stone. The process deposits layers of different minerals at different times, often leaving a striped bed of alternating rock types behind.

The Akilia rocks also contain graphite, a form of compacted carbon. Mojzsis's analysis of the graphite indicates that it is rich in low-weight carbon atoms, which are typically produced by the metabolic activities of living organisms rather than by natural geological processes. From that evidence, he inferred that the Akilia graphite was the remains of ancient, though unrecognizably compressed, life-forms.

Funded in part by the National Geographic Society, Fedo and Whitehouse visited Akilia, inspected the rocks, and arrived at a different conclusion. The pair published their findings in the May 24 issue of the journal Science.

"These rocks are not as fresh as they were the day they formed," says Fedo. For billions of years, he says, "they've been squashed tens of miles underground. The rocks are so strongly deformed that understanding the original relationships [among different layers] is extraordinarily difficult."

All the same, understanding the processes that made the rock is what he and Whitehouse set out to do. They observed that some of the bands in the rock formation show irregular variations in their thickness, so that they look like chains of meaty sausages attached by more narrow links. Sedimentation doesn't produce that sort of pattern. These bands do not have a sedimentary origin, says Fedo.

Rock Bands Reinterpreted

Rather, says Fedo, we think the green bands are igneous. Igneous rock, unlike sedimentary rock, comes from volcanic activity. If the banded rocks are igneous, the Akilia rocks may well have formed in the absence of life-sustaining oceans, making them much less likely to have harbored early life.

"They've become banded because these rocks are extremely deformed" by the intense heat and pressure beneath the Earth's crust, says Fedo.

As for the evidence from the graphite, Fedo cautions against jumping to conclusions. "There are non-biological mechanisms that are capable of producing carbon that is very light, that mimics the values that living things generate," he says.

So if the banded rock isn't a product of sedimentation, what is it? Fedo thinks the green, iron-rich igneous rock formed first, in the aftermath of a volcano, but that later cracks filled with heated water carrying dissolved minerals. Those minerals stuck in the cracks and hardened into veins of white quartz.

Meanwhile, Mojzsis stands by his interpretation of the data with its older date. The geological picture is extremely complicated, he says, expressing concern that Fedo and Whitehouse may have oversimplified data in the process of their analysis.

Fedo acknowledges that the new interpretation is controversial, and the true age of life on Earth is bound to be contested for some time.