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Unknown Unknowns
Scientists are tapping into the secret wisdom of trees—even when they don't know what they're looking for.

In 1901 an astronomer named A. E. Douglass had a revolutionary idea for how to study the effect of sunspot cycles on the earth’s weather and climate: cut down a tree and look at the growth rings on a cross-section of its trunk. At low elevations, he found, the width of the rings correlates with precipitation. Only later did he realize that the rings could also be used as a dating tool to help archaeologists figure out the age of ancient civilizations, Viking ships, Stradivarius violins, framed paintings. Almost anything made of wood, it turned out, held a hitherto invisible record of the time and conditions in which the tree had lived.

Back then, Douglass measured rings with calipers. Now, at the Laboratory of Tree Ring Research, which he founded at the University of Arizona 77 years ago, modern-day dendrochronologists have a host of high-tech tools that let them ask and answer complex questions about the conditions in which trees have lived. These advances have inspired them to create and maintain an archive containing millions of tree samples from around the globe, some dating back thousands of years.

The lab’s director, Thomas Swetnam, likens the archive to a vast library filled with many volumes whose literary value has yet to be determined. “The tree-ring sections are like books, and the rings are like pages—and we’ve read just some of them,” he says. “We’re taking care of the wood because we know from past experience that we’ll develop new tools and new ways of measuring.”

Like Douglass before him, Swetnam understands how unforeseeable insights and technological developments can lead us toward new discoveries and conclusions . “There’s the known unknown,” he says, “and then there’s the unknown unknown.” It’s a Lewis Carroll–esque way of describing two parallel paths to discovery. Scientists traveling the first believe they can see the shape of their elusive quarry, like a hole in a mostly completed jigsaw puzzle. Scientists on the second path don’t even realize they’re on it until they reach the end, where some combination of technological advancement, creativity, and/or luck reveals an answer to a question they had never thought to ask.

Swetnam refers to advances made under this latter set of circumstances as “Who’d have thunk it?” discoveries. One example from the 1970s came by way of some astrophysicists who wondered whether the explosion of a particular star back in AD 1054 had affected the atmospheric composition of the earth, some six light-yearsaway. They tested the isotopes of an ancient tree in the Laboratory of Tree Ring Research archives. Within the ring pattern that corresponded to that year were clear signs of high-energy particles emitted by the star, particles that a scientist of A. E. Douglass’s era would never have had the means—or, for that matter, the notion—to measure.

One wonders: What other natural archives are out there, hiding in plain sight, waiting for someone to unlock their secret wisdom?

When a type of surface-dwelling plankton called foraminifera die, they sink to the ocean floor, forming layers of sediment that date back as many as 150 million years. Last year, researchers at the University of Wisconsin–Madison announced that they had measured the isotopic signature of ancient, fossilized foraminifera at a scale about a million times smaller than had previously been possible. In so doing, they were able to pinpoint not only when the plankton had lived but also what the ocean temperature had been at the time. It’s a “powerful record” of long-term climate change, says the geoscientist John Valley, who took part in the study.

The ion microprobe that his team used isn’t a new invention, but the technology behind it has greatly improved over the past 30 years. In addition, Valley and his colleagues have developed protocols that heighten the resolution of its measurements. Recently a team of visiting Japanese marine biologists brought ear stones from a rare species of eel to Valley’s lab, where they used his microprobe to help determine how cold the water had been in the creatures’ birthplace, the exact location of which was a mystery. The temperature data they gathered led to a new set of underwater coordinates—where the scientists eventually found the eels, hatching.

It can be scary to admit just how big a part serendipity plays in our ability to measure—and thus to understand—the natural world. We like to believe that our scientific inquiries are utterly methodical and under our control. On the other hand, it can be exciting to realize that they’re not. Research has always been driven as much by our innate love of seeing and learning things for the first time as by our need to solve problems or complete theories. What could be more gratifying to the explorer in all of us than adding the final piece to the jigsaw puzzle and discovering that the puzzle you just solved is different from the one you thought you had started?

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image of Kim Tingley
Kim Tingley is a regular contributor to OnEarth and the New York Times Magazine. She has an MFA in nonfiction writing from Columbia University and in 2012 received a Rona Jaffe Foundation Writer’s Award, given annually to six female writers who demonstrate excellence and promise in the early stages of their careers. MORE STORIES ➔