If our understanding of why early humans walked out of Africa is one day vastly refined, it may be because Tom Johnson motored out on some of the continent’s largest, deepest lakes and peered into life 100,000 years ago. Already, his insights derived from sediment core samples are reshaping discussions of climate change and evolution.

But mostly, our perception of the planet will change because Johnson wasn’t big enough for football. He grew up in landlocked Virginia on Minnesota’s Iron Range, dreaming of becoming Jacques Cousteau. “How do you get out of a mining town in northern Minnesota?” he asks. “You either play football or become an oceanographer.”

Several decades later, after studying at Scripps Institution of Oceanography, conducting oceanographic research for the Coast Guard during the Vietnam War, and heading the oceanography program at Duke University, Johnson is back in Minnesota…studying lakes.

Tom Johnson examines a sediment core from the north basin of Lake Malawi, East Africa.

Tom Johnson examines a sediment core from the north basin of Lake Malawi, East Africa. Photo by Josh Kohanek.

It was an offer he couldn’t refuse. In the mid-1990s, the University of Minnesota lured him from Duke to Duluth to found the Large Lakes Observatory, the country’s first institute devoted to an international program of great lakes research, from Lake Superior to Lake Baikal in Siberia.

“The need for research on large lakes is as acute as the need for research of oceans,” Johnson says, pointing out that thousands, if not millions, of people depend on these lakes for food, water or work.

Lake Superior and Climate Change

The vast reservoirs are also bellwethers of climate change, and their sediment beds—as deep as they are old—offer remarkably rich histories of ancient Earth. But you wouldn’t know this from the relatively tiny percentage of government research money devoted to lakes (they aren’t as “sexy” as oceans, admits a fellow LLO researcher), an imbalance Johnson has worked to change.

In Johnson’s office, located on a hill overlooking Lake Superior, rests an antique Japanese fishing float and a vintage boat bumper woven from reed-like wood, totems of his fascination with the exotic and the deep.

In the 1980s, he first ventured to East Africa to send long tubes into some of the world’s oldest lakes, pulling up sediment from 10,000 years ago. The stuff reads like a textbook on the paleoclimate record—a thriller, actually. Johnson helped launch the first major research boat on Lake Tanganyika, and later discovered evidence of African megadroughts that repeatedly emptied enormous waters, such as Lake Victoria. It’s a find that helps illuminate the pace of evolution, since hundreds of fish species now thrive in the lake that was dry not so long ago.

More recently, Johnson and a multinational team of researchers drilled much deeper into human history. Living in a converted shipping container on a drilling barge for six weeks in the searing tropics, Johnson gathered core samples that revealed a shift from extreme drought to a wetter, more stable climate—at around the same time as early human populations are believed to have expanded and migrated out of Africa.

Back in the observatory, Johnson continues to sift through ancient sediment, thereby transforming our understanding of the planet’s climate history and its effects on ecosystems. And if Johnson never does step into Cousteau’s salty sea flippers, that’s OK with him.

“There is a gold mine of research to be done on large lakes,” says Johnson. “It’s a good time to be here.”

This article originally appeared in the Winter 2009 issue of Momentum magazine, Ensia’s predecessor, as “Making Waves.”