Kelly Dorgan, 26
Her engineering tricks turned the underground world inside out
"I´ve always kind of liked worms," says Kelly Dorgan as she tries to coax one to begin burrowing through a tank of gelatin. This particular specimen, a six-inch-long sandworm provided by a local bait shop, isn´t cooperating, and Dorgan, a Ph.D. candidate at the University of Maine, gently prods it while she readies her video equipment. She needs good footage for an upcoming paper. Dorgan turns on a backlight. The worm writhes on the surface of the gelatin. Dorgan adjusts her monitor. The worm noses around. Dorgan nudges. The worm wriggles. Nothing happens. Fi-nally, our little star acquiesces, and with a sudden display of resolve one doesn´t expect from an invertebrate, plunges its head into the gelatin and executes a swift, surprisingly elegant descent.
Working mostly in this chilly lab, Dorgan has challenged a century-old theory, endorsed by none other than Charles Darwin, about how worms move. The work has quickly established her as an authority on the world underground. Steven Vogel, a professor of biomechanics at Duke University, says "Anyone who´s working in her area is going to start by checking her papers or writing her an e-mail."
Worms are notoriously difficult to observe, and biologists have never been able to say definitively how they move. Darwin, who always liked worms himself, was one of the first scientists to seriously investigate the question. He didn´t believe "that the ground could yield on all sides" to a worm nosing through soil. When push came to shove, he thought, worms swallowed a path through the earth. His theory held for more than 120 years but led later scientists to wonder why burrowing should be so popular. Compared with other ways of getting around (walking, swimming, flying), eating through mud seems extraordinarily inefficient.
Dorgan thought worms must use some kind of trick to help them through the mud, but to investigate the forces involved would require the equivalent of a degree in engineering. "My background was pretty much straight biology," she says. "I didn´t know any of the physics I needed." To remedy that, she took engineering
classes by day and Googled shop tricks by night. She eventually came across a method known as photoelastic stress analysis, which employs an elaborate setup of polarized light and camera filters to measure the stress placed on an object. She found a seawater-gelatin mixture that had the physical properties of marine sediment and let it set in a tank. Then she added a worm and filmed it burrowing.
By studying the stress fields around the worms, Dorgan discovered that they actually launch their mouths inside out like a wedge to pry open the mud. Then they ease into the space opened by the crack. To keep moving, they just keep leveraging the crack. In engineering terms, this is known as crack propagation, and Dorgan´s studies suggest that it costs the worms much less energy than having to ingest every inch of mud in their path.
Her finding has changed scientists´ understanding of the entire underground ecosystem. Everywhere biologists look now, they´re realizing that burrowers such as clams, sea urchins and even growing root tips are really living levers. Next, Dorgan plans to study the large-scale effects of burrowing in coastal areas, where worms can mix up the top four inches of the mud, releasing buried nutrients and churning up pollutants like DDT. Scientists have studied the phenomenon, known as bioturbation, since at least 1881, when Charles Darwin made the first serious attempt to describe it.-Adam M. Brightsingle page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.