The Disappearing Spoon podcast

Topsy-Turvy Tales from Our Scientific Past
June 26, 2024 Environment

The Mysterious Mote

This bonus episode highlights an excerpt from Ferris Jabr’s book Becoming Earth.

Bundle of bacteria on Oleander plant

Russ Schnell’s professors mocked him for believing that plants somehow caused hailstorms. He not only proved them wrong, but uncovered profound connections between life, earth, and the air above. This bonus episode of The Disappearing Spoon tells the story of Schnell’s astounding discovery via an excerpt from Ferris Jabr’s book Becoming Earth.

About The Disappearing Spoon

Hosted by New York Times best-selling author Sam Kean, The Disappearing Spoon tells little-known stories from our scientific past—from the shocking way the smallpox vaccine was transported around the world to why we don’t have a birth control pill for men. These topsy-turvy science tales, some of which have never made it into history books, are surprisingly powerful and insightful.


Host: Sam Kean
Senior Producer: Mariel Carr
Producer: Rigoberto Hernandez
Associate Producer: Sarah Kaplan
Audio Engineer: Jonathan Pfeffer


Hey, everyone. First a little housekeeping. We’re hard at work on the new season of Disappearing Spoon, which should be out starting this fall—so stay tuned for that.

In the meantime, here’s a little summer bonus. It’s an episode adapted from a new book called Becoming Earth: How Our Planet Came to Life by Ferris Jabr. It’s out now from Random House. I hope you enjoy it as much as I do.

Russ Schnell rushed into the lab and threw down his things. If he didn’t hurry, he’d be late for the party.

It was a warm summer evening in 1970. Schnell was a short, slender man with thick blond hair who worked in a meteorological lab at the University of Alberta in Canada. He liked organizing parties on the banks of a nearby river, with rafting and a big bonfire.

Schnell had just picked up hotdogs to roast that night. He didn’t allow booze at these gatherings, which meant that the party wouldn’t really get going until he arrived with the hotdogs. That’s why he hated being late.

Along with the hotdogs, Schnell was also carrying something a little less appetizing: a plastic bag full of grass. It was part of his research. He was investigating a bold—or what some called a kooky—theory: that plants played a major role in producing hail and other forms of icy precipitation. His advisors didn’t put much stock in the idea, but they said that if he wanted to waste his time with it, he was free to do so.

After hurriedly completing some essential tasks in the lab, Schnell turned to the bag of grass. He had a simple experiment planned, but he was already late. So, with a sigh, he decided it would have to wait. He tossed the bag on a shelf, grabbed the hotdogs and set out for the river.

Schnell soon forgot about the bag—a small oversight that eventually led to a major scientific breakthrough. If he’d returned the next day and run the experiment, it would have been just another failure in a long line of them. Instead, the bag sat neglected on the shelf for ten days—so long the grass started to rot. When he finally remembered the bag and opened it, he found a putrid white fluid sloshing around inside. 

Little did he know that something in that fluid would soon revolutionize our understanding of weather—and, ultimately, of the planet as a whole. 

Ever since his childhood, Russ Schnell was mesmerized by the atmosphere. Growing up in rural Alberta, he witnessed lightning strikes and torrential downpours every summer. He especially liked to watch storm clouds form: they were great swirling masses of vapor, like whirlpools in the sky, sucking up air and dust.

He was also fascinated by hail—partly because hailstones often destroyed the local wheat, oat, and barley crops. Farmers watched every storm anxiously, and Schnell quickly learned to determine which clouds produced hail. Hailstone clouds ride lower in the sky and are more tumultuous, with more movement and circulation. The fiercest hail clouds spit out balls of ice the size of oranges.

As a student at the University of Alberta in 1968, Schnell spent his summers assisting a group of atmospheric scientists. One of the project leaders asked him to investigate the formation of hail­stones. How exactly did clouds produce such large chunks of ice?

Believe it or not, water doesn’t automatically freeze at 32°F. In fact, pure water can remain liquid to about −40°F. To freeze above that temperature, water needs a seed, or what’s called an ice nucleus. It’s a tiny particle that acts as a geometric template. It aligns water molecules into an organized solid crystal.

At the time, most scientists thought that water vapor in the air condensed on floating particles of dust and soot. Then, some of this suspended water could freeze if the air was cool enough, forming ice crystals. But no one knew what kind of particles made the best seeds for incipient crystals, nor how they grew into hailstones. Schnell’s task was to find the mysterious mote that turned cloud water into ice.

Schnell thought back to the hailstorms he observed growing up. They always seemed to form over forests and other densely vegetated areas. He began to wonder whether ice nuclei were maybe more than just inert bits of dust. What if some nuclei were spewed out by trees, or what if churning storm clouds vacuumed something up from plants? He was certain that trees and other plants had something to do with clouds and hail.

When he told the senior scientists in his lab about the idea, they chuckled at how naive he was. Trees helped return water to the atmosphere, of course, but apart from that, what could they possibly have to do with clouds, much less hail?

But Schnell’s background gave him a unique perspective. Hail only forms regularly in certain parts of the world: places like Colorado, Argentina, and Alberta, where he grew up. Meanwhile, his professors had mostly grown up in places like England, which almost never gets hail. In fact, some of them had never seen hail before coming to Alberta. 

Despite Schnell’s pleas, his senior colleagues were unsympathetic. They adhered to the prevailing theory at the time: that clouds and hail were seeded by dust and soot alone. When Schnell insisted otherwise, they basically shrugged and said, Prove it.

So Schnell spent a few weeks roaming nearby forests and fields. He would grab handfuls of grass and pluck leaves from poplars, aspen, and conifers. In the lab, he’d cut off a small piece of each one and slosh it around in a vial of water to capture whatever invisible particles were on its surface.

Then he’d used a syringe to remove some water from the vial and care­fully place dozens of drops on a copper plate whose temperature he could control precisely. He covered the plate with a glass dome and gradually lowered the temperature. If the drops froze before the plate reached about 5°F, then he’d know they contained a nucleus that helped ice crystals form.

But they never did. No matter what grasses or leaves he tried, he just couldn’t get ice crystals to form above 5°F. Maybe his professors were right.

Then came the night of the party in 1970, when Schnell tossed the plastic bag of grass on a shelf and forgot all about it. Ten days later, he peeked inside and discovered the funky white fluid.

Rather than throwing it out, Schnell decided to test the rotten grass water on the copper plate. Why not? What harm was there? To his astonishment, the water froze at just under 30°F—a much higher temperature than ever before. Something in that putrid brew—something potentially biological—was turning water into ice.

Schnell moved to the University of Wyoming for graduate school, where he continued his studies on plant-derived ice nuclei. He suspected that a plant-loving fungus was involved. So he asked a colleague in the botany department, a man named Richard Fresh, to take a look at his leaf sam­ples.

Fresh discovered that the ice-forming molecules were in fact pro­teins clinging to the shell of a rod-shaped bacterium. That bacterium was called Pseudomonas syringaeP. syringae tended to live in soil and on plants. Crucially, the proteins on its shell mimicked the shape of ice crystals. As a result, they provided a perfect template to organize free-flowing water molecules into a crystal solid.

On the ground, P. syringae bacteria gave plants frostbite. They ruptured their tissues in order to access their nutrients. Then when storm clouds sucked up air and dust from the ground below, they would inevitably pull in var­ious microorganisms as well. Once inside the clouds, P. syringae and its proteins could then seed ice crystals and hailstones.

Thrilled by these discoveries, Schnell embarked on a globe-spanning research expedition. First, he traveled west from Canada across the central United States. Then he flew to England and traveled east across Europe and through Russia on the Trans-Siberian Railway. Before returning home, he toured Japan, Thailand, India, Nepal, Iran, and parts of Africa.

Skinny and disheveled, Schnell lived frugally on these trips, eat­ing and lodging for as little as $100 a month. Whenever he had the opportunity he would stop and collect leaf litter—on the side of a road, in a field, in a grove of trees. He’d then store it in a plastic sandwich bag.

Back in Wyoming, he tested dozens of samples from all manner of ecosystems and climates. In every single one, he found active ice nuclei produced by P. syringae and other microbes. No scientist had ever seriously proposed that a microbe could freeze water, let alone change the weather. Yet here was the proof.

Schnell soon realized that ice-making microorganisms were important for more than just hail formation. Once they got into the atmosphere, they would also increase the chance of rain. Only a small percentage of all clouds grow heavy enough to rain. The vast majority just evanesce.

But the presence of ice nuclei can dramatically change the odds. An ice nucleus can start a chain reaction. It rapidly freezes lots of cloud water, draw­ing in even more water and swelling a cloud until it bursts. The pro­teins that P. syringae makes are the most effective ice nuclei ever discovered. Schnell thinks they are a crucial component of the water cycle in ecosystems across the planet. As he says, “Almost all rain that falls on land, even over the Sahara and along the tropics, is first an ice crystal.”

The private sector quickly recognized the potential of Schnell’s discovery. By the 1980s, a company called Snomax had patented the process of creating artificial snow using sterilized proteins isolated from massive vats of P. syringae. Ever since, ski resorts around the world have relied on microbial proteins to blanket their slopes.

In contrast, the scientific community largely ignored weather-changing microbes for several decades. Scientists regarded them as an intriguing but trivial aspect of meteorology, not worthy of serious research. In recent years, however, attitudes have started to change. Climate change has pushed scientists to reexamine the complexities of the atmosphere, and astonishing new discoveries have come to light.

It’s now clear that P. syringae is far from the only organism that can turn water into ice. Numerous bacteria, algae, lichen, and plankton, on land and out at sea, all produce ice-seeding proteins.

Strong winds, updrafts, thunderstorms, and dust storms routinely whisk these tiny creatures into the atmosphere, there they form celestial colonies for weeks at a time before returning to the Earth’s surface in the very precipitation they stimulate. In doing so, these accidental aeronauts may influence the planet in profound ways that until now have been largely neglected.

The idea that the atmosphere teems with unseen life has intrigued scientists since the seventeenth century. Antonie van Leeuwenhoek was one of the first people to observe microbes through a microscope. He surmised the existence of “living creatures in the air, which are so small as to escape our sight.”

In the 1800s, while aboard the HMS Beagle, Charles Darwin collected wind­swept dust over the Atlantic that was later revealed to be full of mi­crobes. And in the early 1900s, a plant pathologist with the U.S. Department of Agriculture, convinced Charles Lindbergh and Amelia Earhart to furnish their aircraft with metal cylinders de­signed to capture microorganisms.

Only in the late twentieth century, however, thanks to Russ Schnell and others, did researchers begin to regard airborne microbes as more than passive travelers.

When scientists collected fresh snow on multiple continents and searched them for microscopic life, nearly every sample—including those from Antarctica—contained ice-nucleating microbes. Scientists have also discovered a variety of microbes in the centers of hailstones.

Other researchers have analyzed cloud water. Inside, they measured, on average, tens of thousands of bacteria in each milliliter. Microbes can even trigger what’s called a bioprecipitation feedback loop. The more intense a rainstorm, the more microscopic life from the ground gets kicked up into the air. This in turn produces more frequent and more intense storms in the days and weeks ahead.

Scientists once thought that ice-nucleating proteins evolved pri­marily as a way for P. syringae and its ilk to feed on plants, and only secondarily as an opportunistic means of air travel. But P. syringae is not always harmful to plants and does not live on them exclusively; it’s also found in rivers and lakes.

Moreover, the ice-nucleating proteins evolved long before anything we’d recognize as a plant even existed—at least 1.75 billion years ago. Back then, these proteins probably helped microbes survive in freezing water, perhaps by sequestering damaging ice crystals out­side their cells.

Over the eons, ocean waves and powerful winds would have carried such microbes into the atmosphere. There they would have encountered many dangers: DNA-warping ultraviolet light, a lack of food, the threat of dehydration. But bacteria with ice-nucleating proteins would have enjoyed a huge advantage over those without. The proteins gave them a return ticket to the surface. And microbes that could survive long enough to travel great distances would have expanded their ranges and possibly found more favorable habitats.

For most of Earth’s history, a span of several billion years, life on our planet was exclusively microbial. Few if any organisms were composed of more than one cell. When multicellular life emerged, it had to fit into this matrix of smaller and more ancient creatures. The rise of plants, fungi, and animals profoundly increased the complexity of Earth’s ecosystems, not simply by introducing larger and more sophisticated organisms but also by spawning countless new relationships between those organisms and their microbial predecessors.

Plants developed a particularly close relationship with the water cycle. They effectively functioned as sponges and pumps, linking land and sky.

At the same time, plants became canvasses and conduits for their microbial partners. These included the microbes that seed clouds and induce rain. The warm, wet regions of the conti­nents grew soft and green with leaf and bud. As plants became stronger and taller, they lofted invisible societies of essentially weightless beings. This amplified their presence in the atmosphere. Together, they pulled water from the soil, pushed it into the air, and called it back again.

Russ Schnell’s instincts were right: trees had everything to do with clouds.

Again, that excerpt came from Ferris Jabr’s new book called Becoming Earth. I hope you enjoyed, and I’ll see you all in the fall.

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