The story of life before animals

It had been a week since the Soviet-era military helicopter dropped him and his colleagues at the edge of a northern Siberian river. And Andy Knoll was still waiting for the ice to melt.

The group needed to get downriver. There lay valleys nestled between huge cliffs of ancient rock that they hoped would reveal clues about what led to an explosion of animal life on Earth nearly 600 million years ago. After a week, they decided to carry their rafts part of the way, slogging through the slush and ice.

Knoll, a paleontologist and professor of natural history at Harvard University, has paddled a raft downstream against whipping Siberian winds, practiced shooting a rifle to ward off polar bears in Greenland, and endured countless nights in tents in remote locations around the globe, from an African desert to islands north of Norway.

"You've just got to go where the rocks are," Knoll said.

Knoll's rocks and research are the subject of an exhibit that opened this month at the Harvard Museum of Natural History in Cambridge. The exhibit -- one room filled with fossils, microscopes and large, explanatory panels -- describes how life developed on Earth out of the primordial soup.

Knoll, 53, is a leader among researchers who explore the forces that may have shaped life over billions of years, when the environment on Earth was harsh and without much oxygen. Named one of the nation's top scientists in CNN/Time America's Best of 2001, Knoll still thrills at the physical challenges of trying to understand the emergence of the earliest life forms.

He and his colleagues describe evolutionary processes that predate what Charles Darwin explained in his theory of natural selection. They focus on events billions of years before the "Cambrian Explosion," the seemingly sudden appearance about 540 million years ago of an array of complex organisms, the ancestors of today's creatures.

They explore complex relationships among species and the consequences of major physical events billions of years ago. Over time, geological events such as volcanic eruptions and shifts in tectonic plates helped give rise to ever-more complex life and an oxygen-rich atmosphere.

"I think the general thing that drives me is very simple," Knoll said. "And that is you can go to a rock in a cliff or a road cut or stream side, crack it open and find in front of you evidence of something that lived hundreds of millions of years ago, or sometimes in my work, billions of years ago."

He first encountered that thrill when he was 12 years old, living in southeastern Pennsylvania. Knoll had joined his older brother on a school field trip to a quarry, where he found his first fossil.

"I was just intoxicated by the experience," he said. "It was the best thing I had ever done."

After high school, Knoll studied engineering at Lehigh University, until he realized that he could combine his love of biology and geology into a career -- paleontology. "It was a great moment in my life."

It was also during this period that he met his future wife, Marsha, who was a student at Connecticut College. Both sang in choruses for their schools and met during a joint concert.

His wife doesn't mind that he's often traveling for weeks at a time to the far corners of the world.

"What line of work can you think of where you get to go to the Arctic or to Africa and actually have something to do there and not just be a tourist?" Marsha Knoll said, adding that they now have friends all over the world.

As a geology graduate student in the 1970s, Knoll began working under paleontologist Elso S. Barghoorn, who had helped pioneer research into life during the Earth's first few billion years.

Since then, Knoll has sought out evidence in the form of fossils, and in the chemical composition and texture of rocks, of what may have driven the Cambrian Explosion.

In one discovery in the early 1980s, Knoll and a colleague analyzed the chemistry of carbon in rocks from the island of Spitsbergen in the Arctic and East Greenland. They found evidence that changes in the levels and types of carbon from about 850 million to 500 million years ago were linked to global ice ages and then a rise in oxygen levels, Knoll said. The glaciers may have slowed the pace of evolution, and the rise in oxygen likely made possible the subsequent emergence of large animals.

Not long afterward, Knoll wrote about this interaction between the global climate, biologic evolution and the carbon composition of rocks.

Pulling those ideas together "was just hugely ahead of what other people were thinking," said biogeochemist John Hayes of the Woods Hole Oceanographic Institution who had collaborated with Knoll on analyzing the carbon samples from Spitsbergen.

While working in China in the 1990s, Knoll and one of his students found 600 million-year-old fossils that included eggs and embryos -- the earliest undisputed evidence of animal life, according to Knoll.

He also has studied stromatolites, domelike structures that scientists believe were created by layers of algae and other early creatures that were surrounded and preserved by sediments. Drawing on 20 years of work, including trips together to northern Siberia, Knoll and MIT geology professor John Grotzinger developed a theory that long-term changes in stromatolites were not caused by biologic evolution -- as scientists previously had thought -- but by environmental changes in the ocean evident in rocks.

Knoll's experience finding evidence of life in ancient rocks qualified him to become a member of NASA's Mars Exploration Rover science team, which has been examining data collected by robots for clues into the planet's history, and whether any form of life ever existed there.

"Mars does serve as a distant mirror on our own planet," he said.

What scientists have learned about Mars so far suggests that young Mars and Earth grew into very different planets and have become even more so, Knoll said.

"Why didn't the Earth become like this?" he asks, leading a visitor around the Mars portion of the Harvard exhibit. Asking questions like that is "fairly addictive stuff."

If you go: The Harvard Museum of Natural History, at 26 Oxford Street in Cambridge, is open seven days a week from 9 a.m. to 5 p.m., except some holidays. For more information, call 617-495-3045, or go to www.hmnh.harvard.edu.