The world's oldest marine sediments

"These are the world's oldest marine sediments ... If we're going to gain any insight into what the surface of the Earth was like 3.85 billion years ago, this is it."

Onsdag d. 20. september 2000
Faye Flam
Emnekreds: Biologi, Forskning, Geologi.

AKILIA ISLAND, Greenland - Nature could hardly have chosen a more inconvenient place to hide what may be the earliest traces of life on Earth.

Even during the brief summer on this treeless, uninhabited island just below the Arctic Circle, temperatures hover around a chilly 40 degrees. Pounding storms and blinding fogs pass over in relentless progression, thwarting efforts to reach civilization's nearest outpost, a three-hour boat ride away.

But Steve Mojzsis, 35, needed to spend part of the summer here, sleeping in a tent, forgoing showers or baths, and using a snowbank as a refrigerator.

Science's understanding of the origin of life depended on it.

Mojzsis, (pronounced Moy-zish), a geologist at the University of California, Los Angeles, had forged a connection to this place by claiming that a rock from Greenland's Akilia Island held evidence of ancient life - perhaps the most ancient ever found.

In 1997, while still a graduate student, the lanky Mojzsis had sauntered up to a podium in front of a major scientific meeting and plunked down the rust-colored, black-and-white-striped rock. There, he announced that this small piece of Greenland held the remains of dead microorganisms.

And it was 3.85 billion years old.

That extreme old age had the audience enthralled. Earth itself is nearly 4.6 billion years old.

Others had found microscopic fossils that seemed to date back 3.5 billion years, but this new claim pushed back the origin of life to a much more chaotic period - 3.85 billion years ago, when Earth was pummeled with meteorites, some of them so big that much of the early oceans vaporized in the collision energy.

If Mojzsis was right, then life had colonized Earth well before that hostile period ended.

"This is where we all came from," Mojzsis said, expressing awe that the microscopic bits of gunk in his rock could be the remains of humanity's early ancestors.

But there was a problem. The rock had been dated indirectly and not everyone was convinced of its age. The Akilia rock was too old for carbon-14 dating and it held none of the other radioactive elements that can be used as natural clocks.

The date of 3.85 billion years had come from other geologists, who had worked for the Greenland Geologic Survey. They had dated the rock by examining the way it fit into nearby rock layers that contained uranium isotopes and thus could be dated.

But with those dates coming under fire, Mojzsis realized that he would have to see for himself. He would have to get to Akilia Island, find the layer of rock that was the source of his increasingly famous sample, and determine the age for himself.

No one knows how life began, or when. It remains one of the biggest unanswered questions in science.

Chemists and biologists are trying to figure out what chemical building blocks came together, and how they assembled themselves into the first living things.

Geologists, meanwhile, are using whatever clues linger on the planet to figure out when this happened.

Some of those clues come from Greenland. Its bedrock is one of the last remaining pieces of early Earth, dating back 3 billion to 4 billion years. On most other spots on Earth, rock that old has either eroded or succumbed to the perpetual turnover of Earth's crust.

Most of Greenland is covered in ice, but the few exposed parts around the edges may offer clues to what the planet was like back when life began.

Even if they cannot sort out all the details, scientists are hoping to answer some more cosmic questions: Was the origin of life an improbable fluke? Or, was it an inevitable natural process that has happened billions of times throughout the universe?

NASA has banked on life being common, pouring its resources into the search for life on Mars and beyond.

Mojzsis realized his claim of early life could help the case for life on Mars. That planet, 3.85 billion years ago, apparently flowed with oceans and rivers. If life had already colonized Earth, then why not Mars as well?
Natalie Caciagli and Craig Manning in the dinghy After months of preparation, last July found Mojzsis standing on Akilia Island's ancient rock layers. Along with him were three UCLA colleagues, Craig Manning, Natalie Caciagli and Mark Harrison, decked out in waterproof boots, jackets and rain pants.

From Los Angeles, it had taken four flights and a boat ride over the course of four days, including a provisioning stopover at one of the two grocery stores in Nuuk, the brightly painted fishing village of 14,000 that is Greenland's capital.

Winding over the rocky ground of the half-mile-diameter island was an uneven rainbow of rust, white, black, and varying shades of gray. Billions of years have bent and deformed these bands of solid rock, folding them around like so much toothpaste.
Craig Manning and Mark Harrisonin at work on Akilia Island "These are the world's oldest marine sediments," said Harrison, 48, who had collaborated with Mojzsis from the beginning on work that led to the early-life claims. "If we're going to gain any insight into what the surface of the Earth was like 3.85 billion years ago, this is it."

To Mojzsis, Akilia's Arctic landscape suggested something out of J.R.R. Tolkien. Rocky ridges rose like castles and towers, dwarf trees snaked along the ground, pillows of kelly-green moss surrounded hundreds of glassy pools. Lichens bloomed in strange varieties - orange and yellow ones that splashed over the rocks like paint, black ones that sprouted in the cracks like exotic mushrooms.

On one side of the island, an iceberg rose above the water like a white pyramid.
Craig Manning, Mark Harrison and Faye Flam on their way Although perpetual daylight allowed Mojzsis and his team to work nearly round-the-clock, exhaustion led the group each "night" back to their four tiny tents, pitched on a rare stretch of flat earth on Angissorssuaq Island, less than a quarter mile from Akilia. The group members hopped between the islands on a tiny yellow fishing dinghy.

They gathered for meals in the kitchen tent, eating fresh cod, canned kippers, and bricklike loaves of Danish rugbred, and drinking Scotch on chunks of 10,000-year-old ice they had chipped from a nearby iceberg.

Day after day, they drew maps of the rock layers and chipped away dozens of samples with their geology hammers. They focused on a layer called the banded-iron formation - a milky rock containing thin layers of black-and-rust-colored minerals - that cropped up in different spots around Akilia.

This banded iron was the source of the rock Mojzsis had used to make the claim for ancient life. Analyzing samples in his laboratory back at UCLA, he had found minuscule bits of carbon, which appeared to have come from living matter. Not all carbon comes from something once alive, Mojzsis explained, but scientists have devised a test for a biological origin.

Carbon comes in several forms, or isotopes, that differ by weight. For various reasons, living things do not take up carbon-13 as easily as carbon-12. So the remains of living matter contain relatively less carbon-13.

The carbon collected from this banded-iron layer held a clear signature of ancient life, Mojzsis said. It actually held even more information. The ratio of C-12 to C-13 suggested relatively complex organisms - still single-celled but intricate nonetheless. Whatever had left the carbon in this rock had been evolving for some time.

It would appear, he said, that life had thoroughly taken over the planet even earlier than 3.85 billion years ago - if the dating of the rock was correct.

For several weeks the weather remained cool and storm-free as Mojzsis combed the banded-iron formation for just the right twists that would help him date his 3.85-billion-year-old rock.

There were calm, gray days when the sea turned to glass, punctured by the occasional iceberg, and sharp, windy days when the tortured rock formations sparkled with flecks of mica.

Often at midnight they would see soft pink sunsets that blended into sunrises, as if the sun had bounced off the northern horizon. One night a full moon - salmon pink - peeked over the other side of the sky.

But two weeks into the trip, standing atop the jumbled layers, Mojzsis realized that Earth's story was harder to read than he had expected.

British geologists Clark Friend and Allen Nutman, who had surveyed the area years before, had determined that the banded-iron formation - from which the famed samples of Akilia rock were taken - formed at least 3.85 billion years ago. That team had dated the formation by observing its "cross-cutting relationship" with a rock layer called gray gneiss.

At some point in time, the gray gneiss had erupted as magma and burst through the existing banded-iron formation, they had argued, so the banded iron was at least that old. Happily, the eruption of the liquid gray gneiss could be dated because it contained tiny zircon crystals, which held atoms of radioactive uranium.

Nutman and Friend had concluded that gneiss was 3.85 billion years old - so the carbon-bearing banded-iron layer was even more ancient.

But that conclusion wasn't as clear to Mojzsis and his team. The layers were so bent and contorted that in most places, there was no telling what parts had formed when.

After days of repeat visits to Akilia, they finally found a few of these cross-cutting relationships, plus a different vein of gray gneiss that seemed to cut through the banded iron.

Realizing that others might not agree with their interpretations, they prevailed on Friend and Nutman - who happened to be in Greenland on another project - to drop by Akilia and give a second opinion.

The two British geologists spent two hours tromping around Akilia on a drizzly Sunday morning - enough time to confirm that all the team's examples of the banded iron did, indeed, predate the gray gneiss. Determining the actual ages would come later, back in the laboratory.

Just as they left, a storm churned the seas. The yellow fishing dinghy the team had been using to get from island to island filled with water faster than the scientists could bail.

That night, the team members' excitement over support for their early-life hypothesis was drowned in driving rain and winds that reached 60 m.p.h., leaving them huddling for warmth inside buckling tents.

The next day the sun came out, shining on hundreds of ponds born overnight.

"We got more than I ever expected," said Mojzsis, as he prepared to return to the United States after nearly a month in Greenland. Within his 640 pounds of samples, he said, were more clues about the early Earth.

"What we're really interested in is the stage setting - the conditions under which life emerged," he said.

Astronomers know that the sun was 30 percent dimmer 4 billion years ago, but somehow the atmosphere kept the planet from freezing. In this puzzle might lie some clue to the origin of life. The answer, if it is to be found, would come from the rocks formed during that period.

Back in Los Angeles this week, Mojzsis said he and his colleagues had analyzed many of their samples - calculating the ages of the uranium-containing rocks and confirming that carbon-containing samples held the signature of life.

The group has submitted its findings to scientific journals and is awaiting publication.

Next summer, Mojzsis plans to further extend his search for life's beginnings.

"We spent eight days on Akilia just mapping one corner," he said. "Looking at all those other islands marching out into the sea - who knows what else is out there."Faye Flam's e-mail address is