Small tasters: Pictured are three taste buds on the tongue of a mouse. Each one is half as wide as a grain of salt. Taste cells, which appear here as red and green, bunch together to form the taste buds. The red cells taste sour things. It’s not clear yet what the green cells taste. Courtesy of Thomas Finger

It was an exciting day when Thomas Finger looked inside the nose of a small black mouse. Finger had borrowed the animal from another scientist. It was not your average mouse.

The mouse’s genes had been changed so that the taste buds on its tongue turned green when you shined light on them — like a secret message written in secret ink.

But no one had ever looked inside its nose. When Finger finally did look there with a microscope, he saw thousands of green cells dotting the soft pink lining. “It was like looking at little green stars at night,” says Finger, who is a neurobiologist at the Rocky Mountain Taste and Smell Center at the University of Colorado in Denver. (A neurobiologist studies how the nervous system develops and functions.)

Seeing that green starry sky was Finger’s first glimpse of a new world. If he and other scientists are right, we don’t taste things just on our tongues. Other parts of our body can also taste things — our nose, our stomach, even our lungs!

You might think of taste as something that you experience when you put chocolate in your mouth — or chicken soup, or salt. But for you to taste chocolate or chicken soup, special cells on your tongue have to tell the brain that they detected chemicals that are in the food. We have at least five kinds of these chemical-detecting cells (commonly called taste cells) on our tongues: cells that detect salt, sweet compounds, sour things, bitter things and savory things like meat or broth.

You might call these five things the primary colors of your mouth. The unique taste of every food is made up of some combination of salt, sweet, sour, bitter or savory, just as you can make any color of paint by mixing together bits of red, yellow and blue.

It’s these chemical-sensing cells that scientists are now finding all over the body.

“I’ll bet you that in terms of total number of cells,” says Finger, “there are more [taste cells] outside the mouth than inside the mouth.”

This gives us clues about other functions the sense of taste has in our bodies. It could also help scientists find new treatments for certain diseases.

Fish skin: more than a feeling

It’s an exciting time for scientists who study taste. Finger spent 30 years working toward this big moment. Some of the first clues came from fish.
Back in the 1960s, scientists looking at fish skin under microscopes discovered that the outside of a fish’s slippery body is dotted with thousands of funny cells shaped like bowling pins. Those funny cells look just like the chemical-detecting cells on your tongue. At the time, no one was sure what those bowling-pin cells on fish skin did. But years later, scientists found that they actually can taste. When food chemicals were sprinkled onto the fish skin, those cells sent a message to the fish brain — just like the cells on your tongue tell your brain when you taste food.

Nosey tasters: Taste cells on the inside of the nose of a genetically engineered mouse appear green under the microscope. Those taste cells talk to the treelike branches of nerve cells, which are red in this picture. Credit: Thomas Finger

For fish, being able to taste things all over their body comes in handy. Some fish called searobins use this to find their next meal. When searobins poke their pointy fins into the mud on the seafloor, they can “taste” the worms they’re looking to eat. Other fish called rocklings use these cells to sense the presence of larger fish that might want to eat them.

In these cases, the buried worms and big fish leak small amounts of chemicals into the water and mud. Taste cells on the skin of searobins and rocklings detect the chemicals (sort of the way you might be able to taste what’s in the bathwater after your filthy little brother sat in the tub for a while).

As Finger studied searobins, goldfish and other wet critters, he began to wonder whether land animals like cats, mice and people could also sense taste outside of their tongues. “Why wouldn’t it be a good idea?” he asks. “The more information you get from your environment, the better off you are.”

Peeling mud

But finding taste cells on land animals wasn’t easy. Unlike fishes’, their skin is covered in a dry crust of dead cells, like the layer of cracked mud that forms as a water puddle dries. A taste cell hidden under that crust wouldn’t function. It needs to come into contact with chemicals in the outside world in order to detect them. So Finger decided to look at the wetter, fishier parts of our body. He started his search deep inside the nose.

That’s when he borrowed the mouse with the green taste buds — and found those green, bowling pin-shaped cells inside its nose. The cells were scattered instead of being clumped together, as they are in the tongue. But one thing was for sure: Those cells could taste.

When Finger tested them, the cells contained the same special proteins, called receptors, that your tongue uses to detect chemicals in food. Different kinds of receptors detect different kinds of chemicals — like sugars, sour things and so on. Those in the mouse’s nose specialized in detecting bitter chemicals.

Since Finger’s discovery of this in 2003, other scientists have found bitter-sensing taste cells inside the hundreds of branching tunnels that move air through the lungs of animals.

Some scientists have also found taste cells along the path that food travels through a person’s body — a journey of at least 12 hours. From the stomach, where food is first digested, those taste cells can be found all of the way to the large intestine at the lower end. Some in your gut taste bitter things, others scout for sweet sugars.

(Not) tasting your poop

“There is an enormous number of these cells in the lower gut,” notes Enrique Rozengurt, a biologist at UCLA (the University of California campus in Los Angeles) whose team first found taste cells in the gut in 2002. “Why do you have all of these receptors?” asks Rozengurt. “There are some very profound possibilities.”

It might seem like a really bad idea to have taste cells beyond the tongue. In your nose, wouldn’t you taste salty buggers? And wouldn’t you also taste the brown gooey stuff in your large intestine — which is pretty much just poop waiting to be excreted? If we have taste cells inside our body, shouldn’t we be tasting nasty stuff all day long?

No, says Finger. What you experience when your body “tastes” something depends on what part of your brain the taste cells are talking to.

When you put a bitter pill in your mouth, the cells on your tongue talk to a part of your brain called the insular cortex. This part of your brain is part of your moment-to-moment thoughts. It gets the message from your tongue — bitter! And yuck! Immediately, your face scrunches up. You want to spit the pill out.

Your inner worm

But when cells in the gut detect something bitter, they send a little telegram to a deeper, older part of the brain. Scientists call it the nucleus of the solitary tract, but you might well think of it as your inner worm.

This part of the brain takes care of simple things that a mindless worm would do: pushing food through the gut, digesting it and pooping it out. You don’t have to think about those things. They just happen.

Fin tasters: This mud-dwelling fish, called a searobin, has taste cells on its pointy front fins. It sticks those fins into the mud in order to feel around — or you might say, taste around — for worms that it wants to eat. Credit: Thomas Finger

When your brain’s inner worm senses the arrival of something bitter in the intestines, it tells your brain: Stop. You’ve eaten something bad. Get rid of it — quickly! You may suddenly feel sick, throw up, or have diarrhea. And these things happen without any conscious decisionmaking on your part.

The world is full of bad things like poisonous plants and spoiled foods. These are things that bitter-taste cells in your digestive system scout for. Says Rozengurt, they “are there to defend us against all of these harmful substances.”

Bitter sneeze

Bitter-detection cells in your nose and lungs protect you in kind of the same way. Bad bacteria sometimes enter your nose or lungs.They cause infections that can make it hard to breathe. Bitter-taste cells sound an internal alarm when they detect chemicals that the bad bacteria squirt out.

That alarm signals your body to sneeze or cough the bad stuff out. Bitter-taste cells can also trigger a process that tells white blood cells to attack the unwelcome germs.

It makes sense that you’d want to get rid of nasty, bitter-tasting stuff. But your stomach and intestines also have cells that detect sweet sugars. And they send out very different messages.

It’s one thing to taste sugary pancakes and syrup in your mouth, but what about along the rest of the 30 feet that your breakfast travels through the stomach and intestines?

Those other parts of your body also need to know when something sweet has arrived, says Robert Margolskee of the Mount Sinai School of Medicine in New York City. Cells scattered up and down your gut act as a tracking system to let your body know when the sugary food arrives at each location. “It starts things going further down in the digestive tract to digest those things,” says Margolskee.

Scientists have some evidence that the gut also contains taste cells that detect meaty, savory chemicals. Like the sweet-taste cells, these probably also alert different parts of the gut to what’s coming.

Taste medicines

Margolskee lent Finger those green-tongued mice in 2001. In 2009, Margolskee discovered that sugar-detecting cells of the intestine squirt out a messenger substance, called a hormone, that prepares the intestine to soak up sugars. Those hormones also let another part of the body, called the pancreas, know that sugar is on its way. The pancreas oozes out its own hormone — called insulin — that tells other parts of the body, from the muscles to the brain, to prepare for that sugar.

Making drugs that affect the gut’s taste cells could help treat a common disease called diabetes. In diabetes, the rest of the body appears almost deaf to the insulin message that the pancreas sends out. So the muscles and brain don’t take in much of the sugar, a major source of energy, from the blood. A drug that “turns up the sound in these gut taste cells,” says Margolskee, might help the gut and the pancreas more effectively shout out to the rest of the body that sugar is coming — and to get ready.

Some people have another problem called irritable bowel syndrome. Here, food oozes through their intestines too quickly or too slowly, causing painful traffic jams. Drugs that tickle the bitter-detecting cells might help the intestine push food through more quickly and smoothly, reducing belly aches.

Just this past November, scientists made a more surprising discovery: Bitter-tasting cells in the lungs might one day help doctors treat a disease called asthma.

People with asthma have trouble breathing because the airways in their lungs close up. Now scientists have found that some bitter substances actually open  those airways. And these substances do it better than one medicine that doctors frequently use to treat asthma.

It’s was only the latest surprise. People who study taste outside the mouth expect more will keep on coming.

Until recently, says Rozengurt, a universe of taste sensors existed “that we were vaguely aware of, but we didn’t have any clues of how to study. Now we do.”

POWER WORDS

asthma A disease characterized by a difficulty in breathing, and by wheezing, coughing and constricted airways.

gut The intestine.

hormone A molecule the body produces to serve as a messenger to help the body in its basic functions.

insulin A protein hormone that helps the body get energy from fats and carbohydrates.

pancreas A gland behind the stomach that serves several functions, including releasing molecules that help with digestion and releasing insulin.

taste bud Small organs on the tongue that help mediate taste.

The village of Kuujjuaq, in northern Canada, is home to about 2,100 people.

No roads lead to Kuujjuaq. You can only get to this village, high in the Canadian Arctic, by boat or plane. The trees here are stunted and small, but the bears grow big. The 500 kids who live in Kuujjuaq (pronounced KOO-joo-ak) have unusual chores: they help their parents catch fish and hunt caribou to eat. This place might seem far away from the big problems of big cities, like water pollution and air pollution. But even here, people can’t escape those problems. Pretty little Kuujjuaq, with its blue skies and crystal clear waters, also has an invisible pollution problem that rivals any city.

Toxic chemicals have a surprising way of finding their way up here to the Arctic. They are gushed out of factories and cities thousands of miles away, and they travel to the Arctic like birds flying north for the summer. The birds go back home, but the chemicals stay.

Everyone in Kuujjuaq has the chemicals in their bodies. No one knows their full effects, but they may hurt children in a slow and silent way. They could cause babies to get sick a little more often. And they might even cause kids to do worse in school.

No one would have dreamed that people in such a clean and beautiful place could be hurt by pollution from thousands of miles away. Then, in 1989, some scientists made a discovery.

POPs around the world

Eric Dewailly, a doctor at Laval University in Québec, Canada, was studying chemicals called persistent organic pollutants, or POPs. These are chemicals that can hang around for a long time in people’s bodies or in the environment.

Dewailly and his team tested people in the cities of southern Québec (near the border with the United States) to see how much of these chemicals were in their bodies. Dewailly’s team wanted to compare this group with people in the Arctic. They reasoned that people in the Arctic lived far from pollution, and so would probably have lower levels of POPs in their bodies.

So the scientists went up to Nunavik, the remote, northern part of Québec which includes Kuujjuaq and 13 other native Inuit villages. When they tested people in Nunavik they were surprised. People there had five to ten times as much of these chemicals in their bodies as people living in polluted cities. Some of the chemicals came from as far away as Russia!

Scientists now understand why this happens. The POPs include hundreds of different chemicals. Some are used in electronic gadgets like TVs, or in the lights and electrical wiring of buildings. Some are used in paints or for making windows waterproof. Others are sprayed onto crops as pesticides. But POPs have one thing in common: They like to evaporate. Just as a puddle of water dries on a hot summer sidewalk, POPs turn slowly into vapor and drift into the air. Winds can carry them thousands of miles.

POPs travel in the air until they reach a cold place. Have you noticed that on a hot day, a glass of lemonade with ice cubes in it collects little drops of water on the outside? This is because water vapor, which is a gas in the air, “condenses” onto the cold glass and forms those droplets—the opposite of evaporating or drying. The same thing happens with POPs, says Knut Breivik, an environmental chemist at the Norwegian Institute of Air Research in the city of Kjeller.

“Things tend to evaporate in warmer regions and condense when it gets colder,” says Breivik. So when winds carry POPs into the Arctic or Antarctic parts of the world, cold temperatures cause them to condense onto plants or rocks or snow or oceans. And then they stay where they landed and build up over time.

10 million tons

Over the years, more than 10 million tons of POPs have probably floated through the skies to the Arctic. If those chemicals were piled on an area the size of a football field, the pile would rise 700 meters in the air—higher than the tallest building on Earth.

Since the chemicals are spread over the entire Arctic instead of a football field, there’s actually only a small amount in any one place. A swimming pool filled with Arctic Ocean water might contain only a single tiny raindrop of POPs. But these chemicals have a nasty habit of collecting inside animals and people, so even a little bit in the environment can end up causing problems.

POPs tend to stick to the oils and fats in living things, so tiny ocean animals like plankton soak them up, just like a shirt soaks up a drop of spaghetti sauce. Those plankton are eaten by larger animals, which in turn are eaten by even larger animals.

Every time one animal eats another, more POPs enter the larger animal’s body. Animals can’t digest POPs. They take them in the front, but never poop or pee them out the back end. So the POPs collect and collect. The biggest animals, like sea birds, seals, and whales, have the most POPs in their bodies. And these animals are eaten by native Inuit people, who have lived and hunted in Nunavik and other parts of the Arctic for thousands of years.

Two teaspoons

By the time a boy growing up in Kuujjuaq turns five years old, he may have collected one or two little rain drops’ worth of POP chemicals in his body. That doesn’t sound like much—but it’s thousands of times more concentrated than these chemicals are in sea water. In fact, that little boy has as much of these chemicals in his 20-kilogram body as there would be in two and a half million kilograms of sea water—in other words, enough sea water to fill an Olympic swimming pool! Scientists are trying to understand how the chemicals affect kids.

Kids in Kuujjuaq play and joke around.

André Perron/Wikimedia Commons

Dewailly’s team has made many trips back to Nunavik to study the problem of POPs. In 1992 and 2004, they sailed in a ship to all 14 villages along the coast of Nunavik, including Kuujjuaq. The ship stopped at each village, and doctors took blood samples and examined people. They measured POPs in hundreds of newborn babies. Blood samples were taken again when the babies turned one year old. And these babies were studied for years as they grew, to find out how the POPs in their bodies affected them over time.

These studies have shown that POP chemicals affect the health of children in small but worrying ways. For one thing, these chemicals can weaken children’s immune systems, says Pierre Ayotte, a toxicologist who works with Dewailly at Laval University. “Then you’re less able to fight disease,” he says. Babies with the most POPs in their bodies had more ear infections and more infections in their lungs—not minor infections like colds or flu, but serious ones that affect breathing and can sometimes send you to the hospital.

Long division

These chemicals might even affect how well kids do in school. When the babies were 1 year old, the Laval University scientists gave them some tests. They tested how well the babies used their hands. They also tested how well the babies paid attention and learned when they were shown new toys. All of these tests were videotaped, and scientists carefully studied the videos afterward. What they saw surprised them.

Babies with high POPs levels weren’t quite as coordinated with their hands as other babies. They also didn’t pay attention quite as well when they were being shown new toys—they often stared away at other things. And during several hours of tests, these babies became upset and cried more often.

These were small differences. You wouldn’t notice them unless you watched the babies closely. But when the same babies were tested again at the age of 5, the ones with high POPs still did a little worse.

“At later ages you’re still at a disadvantage,” says Gina Muckle, a psychologist on the Laval University team that traveled to Nunavik to test the children. Muckle thinks that even small changes can affect how children do in school as they get older. They could affect how a child responds when taught something hard, like long division—whether they meet the challenge with a positive attitude, or get upset and discouraged. Or they could affect how a child responds to the stress of going to a new school—how well they make new friends, and whether they still do well in class during those awkward times. Little differences, over the years, could add up. “Those effects,” says Muckle, “are likely to be a real disadvantage overall during the life of the person.”

Still trickling

No one was happy to learn that POP chemicals were hurting people in the Arctic. But finding out about the problem gave the Inuit a chance to do something about it. In the 1990s, the United Nations held a meeting, called the Stockholm Convention, to discuss banning many POP chemicals. The Inuit sent people to the United Nations to tell how POPs had affected them. Since 1998, 140 countries have agreed to stop making many POP chemicals. As a result, levels of POPs in the Arctic are falling.

But it will take a long time for the problem to go away. For one thing, buildings around the world still contain many tons of POPs in their paint and wiring. Every day, a little bit of those chemicals turns into vapor and drifts outside. Eventually, it reaches the Arctic.

Researcher Sébastien Roy tests the quality of a lake’s water during the 2004 Nunavik Health Survey.

Isabelle Dubois/NRBHSS

Soil also contains huge amounts of POP chemicals—and the hot blast of a forest fire can send them into the air, just as a hot blow drier causes water to evaporate from your hair. Breivik found that major fires in 2004 and 2006 caused large amounts of POPs to go into the air and reach the Arctic. Many of these chemicals last for 100 years or longer.

Likely suspects

The other problem is that while hundreds of POP chemicals are known, there are probably others that scientists still don’t know about. “There are new compounds that are ending up in remote areas,” says Frank Wania, an environmental chemist at the University of Toronto in Scarborough.

Many POPs contain the element chlorine. But in the last few years, scientists like Wania have been surprised to find that two families of manmade chemicals, which contain the elements fluorine or bromine, have found their way into the Arctic. “We failed to recognize [them] until they were already accumulating in the Arctic,” says Wania—meaning that large amounts of them were turning up in seals, birds and people. By the time the chemicals were discovered and banned, the damage was done.

Scientists want to get ahead of the problem. Wania has surveyed 100,000 industrial chemicals. He was looking for chemicals—you could call them “hoppers,” “fliers” and “swimmers”—which might reach the Arctic. Out of those chemicals, he found 120 likely suspects that he plans to look at more closely.

All of this might seem like a lot of effort. But many scientists think it’s the right thing to do. It comes down to one question, says Muckle—whether we want children to be able to grow and learn to their full potential. “The environmental contaminants are certainly an issue,” she says. “As a society we need to take that into account.”

Going Deeper:

Getting startedYeon Sik Jung puts chemicals onto a silicon wafer at start of an experiment in the clean room. Credit: D. Fox

Watching Yeon Sik Jung’s slow, careful movements, you sense that he’s doing something important. But it’s way too small to see.

Jung (pronounced Yoong) is dressed in white from head to toe. He wears a white jumpsuit, white boots, a white mask with goggles and a white cap on his head.

With a white-gloved hand, Jung lifts an eyedropper and squeezes liquid onto a flat, shiny disk. That glistening drop hides an invisible world. And Jung controls that world. Within, he is creating some of the smallest electric circuits ever made.

Jung works at Lawrence Berkeley National Laboratory’s Molecular Foundry, just outside Berkeley, Calif. A foundry is a place where tools and other parts are made out of metal. Molecules are tiny building blocks in everything from snot to snails to you and me. Put the two words together, and you have a place where scientists use molecules like Legos to build things too small to see.

Jung is currently working on an invention that could help us overcome the challenges of global warming. Another scientist, named Xiaogan Liang (pronounced Lie-Ang), stands nearby. The two scientists are trying to build tiny electrical circuits called solar photovoltaic cells within the drop of liquid. Solar cells can turn sunlight into electricity.

Filthy people

Jung, Liang and I have to wear these white suits, called “bunny suits,” because we’re in a special room called the clean room.

You may not realize it, but people are filthy—even after a bath. Your body constantly sheds flakes of dead skin. Your clothes, hair and shoes let specks of dust loose into the air. Every breath that you inhale contains more than 20,000 pieces of this invisible garbage, twirling around like loose leaves on a windy autumn day. That tiny trash doesn’t usually hurt your lungs, but it would ruin the work that Liang and Jung are trying to do.

Compared with the tiny things that Liang and Jung are building, a single flake of dandruff is huge. “A speck of dust would be like a comet,” says Liang, referring to the huge chunks of ice that fly through space. A comet hitting Earth could destroy a city, and a piece of dust landing in Jung’s little drop of liquid would ruin his miniature world, too.

So we have to cover our filthy selves in these suits. Pumps filter the air to remove any stray bits of dust. No eating or drinking is allowed. We’re not even supposed to fart. “In principle, it is not desirable to do that,” says Liang in a careful, scientific tone. “But we don’t have detectors in here.”

Every rooftop

As Liang talks, Jung lets the drop of liquid spread out on the shiny, mirror-like disk, called a wafer. Then he sets it in an oven heated to 200º Celsius. “That’s it,” says Jung through his mask. “We just need to wait a couple of hours.”

Today’s experiment is so simple that it’s almost boring to watch. But if Jung, Liang and other scientists succeed, their work could ultimately allow people to put solar photovoltaic cells on every rooftop in thousands of cities around the world, which would help reduce the amount of coal, oil and natural gas burned. That, in turn, would reduce the amount of Earth-warming carbon dioxide pumped into the air.

For a long time, photovoltaic cells have been made from a mineral called silicon. To make pure silicon, scientists actually have to melt sand or rock. It means heating the rock to more than 1,000º C—pretty much what a volcano does. And then scientists have to heat the purified silicon again, to 600º C, so it will form pure crystals. “That takes a lot of energy, and energy costs money,” says Larry Kazmerski, an electrical engineer at the National Renewable Energy Laboratory in Golden, Colo. After that, expensive robotic machines have to build patterns onto the silicon. “The processing is very involved and complex.”

So even though photovoltaic cells could help people burn less coal, oil and natural gas, they cost so much that few can afford to buy them. Even today, 40 years after the first photovoltaic cells were invented, few roofs have them.

Nanoscience, the science of very small things, could solve that problem. The term “nano” means one billionth. The term “nanometer” means one billionth of a meter—or about one billionth the length of a baseball bat.

Greasy frying pan

FocusXiaogan Liang works with the “focused ion beam” instrument in the clean room. Credit: D. Fox

Liang, Jung and other nanoscientists are coming up with a new way to build really small things without the need for such high heat and without the help of the expensive robots. The process is called “directed self-assembly,” and it’s surprisingly simple.

You mix a couple of chemicals together, put a drop of the liquid onto a piece of silicon or plastic (it doesn’t really matter what), and then those chemicals do the work for you. As the chemicals dry, the individual molecules arrange themselves into a complicated pattern, like the pattern that your grandmother might stitch on a quilt. For the photovoltaic cells, Liang and Jung want to create row after row of evenly spaced pencils that will stand up like spines on a porcupine.

If you’ve ever watched a frying pan full of grease cool off, then you’ve seen a very simple kind of self-assembly. As the pan cools, the grease forms little round droplets that sit on top the water in the pan. It happens automatically because of the way that grease and water molecules interact with each other.

Another kind of self-assembly happens when snow falls during winter. All by themselves, water molecules latch together to form beautiful, complicated six-pointed stars of ice — snowflakes. Snowflakes are so complicated that you could never cut a real one out of construction paper using scissors. And yet the mindless little molecules do it themselves.

So what if you could learn to make the molecules do what you want them to? What if you could mix two chemicals so the molecules arranged into specific shapes? What if you could control those patterns just by choosing one chemical or another? Depending on the chemicals you mixed, you might get a polka-dot pattern. Or perfectly straight pinstripes. Or spirals. Or a crisscrossed honeycomb, like in a beehive.

Liang, Jung and their boss at the Molecule Foundry (a scientist named Deirdre Olynick) are learning the art of self-assembly. They can create all of those patterns by choosing the chemicals to mix together. Today in the lab, Liang and Jung are making tiny pegs like pencils standing straight up. If it works correctly, each pencil will be exactly the same size, about one ten thousandth as wide as the sharp point of a safety pin.

Interlocking fingers

Solar cells are made of two types of material, one stacked on top of the other. When sunlight hits the cells, it knocks electrons from one layer into the other—creating electricity. (Electricity is the movement of these tiny charged electrons.) Those two layers could sit flat on top of each other, like layers in a birthday cake. But the solar cell works better if the two layers interlock. With an interlocking pattern, the two layers touch each other over more area. It gives the cells a better net for catching sunlight, and they can convert more of the sunlight into electricity. Those tiny pencils that Liang and Jung are making will be the first step in creating layers that interlock like fingers.

Close-up viewXiaogan Liang looks at the self-assembled projects under the electron microscope in the clean room. Credit: D. Fox

Self-assembly avoids the high temperatures used in making pure silicon. Never mind volcano temperatures reaching 1,000º C. Jung and Liang are cooking their drop of liquid at just 200º C—about as hot as pizza is cooked. And because the molecules arrange themselves, Jung and Liang also should not need as many expensive robotic machines to make the complicated patterns that will interlock the two layers in their solar cells.

The big challenges in self-assembly are being clean and using the right recipe. And the recipe that Jung and Liang are using today is simpler than making pizza.

“That’s the point,” says Stefano Cabrini, the director of the Molecular Foundry. “The point of self-assembly is to make something easily that you can produce many, many of.”

Invisible forest

After waiting two hours for the chemicals to bake and dry, Liang and I slip back into our bunny suits and return to the clean room.

As Liang lifts the wafer with a pair of tweezers, it’s hard to see any difference. The wafer looks shiny, just like before. The coating of chemicals on the wafer is very thin—only one ten-thousandth as thick as a sheet of aluminum foil.

In order to see the pattern that those molecular Lego blocks have formed, we need to look at it through a special microscope, called an electron microscope. This microscope is the size of a small refrigerator, with wires coming out on all sides. The picture from the electron microscope shows on a computer screen.

As Liang turns knobs to focus the microscope, a hidden world takes shape.

On the screen we see what looks like a forest of gray pencils standing straight up. If we were looking at red blood cells or little amoebas swimming in pond water, we might need to magnify the picture only 200 times. But in order to see this hidden forest of pencils, Liang has magnified the picture 590,630 times.

Each one of those pencils is only 60 atoms across. Even the most advanced silicon-carving robots today cannot carve shapes this small. But here, the researchers have done it just by mixing a couple of chemicals together. Shake and bake.

Printing money

This pencil-studded wafer that Liang and Jung have made could someday be used to print solar cells onto sheets of plastic, the same way that dollar bills are printed onto paper.

In the factory, a sheet of plastic might roll off of a giant spool. As the sheet of plastic moves, like a conveyor belt, a huge printing press would squish down on it. That printing press would have the same tiny pencil-studded pattern that Liang and Jung made today. It would press that shape into the plastic—“like kids making handprints in the mud,” says Liang. Then another chemical could be painted over the top of the plastic sheet, filling the holes made by the tiny pencils in the printing press and creating a second layer. And abracadabra—you would have a sheet of photovoltaic cells. That sheet would be rolled like toilet paper onto another huge spool.

When people build a house, they could go to the store and buy a few rolls of that solar cell paper. They’d unroll the cells onto the roof of their houses. Unlike toilet papering a house, though, this would be good for the environment. Those solar cells would convert sunlight into the electricity needed to turn on lights and run computers.

If this self-assembly works, it could allow many more people around the world to put solar cells on their buildings. “There is risk. There’s no guarantee it will work,” says Kazmerski. “But the benefit is quite incredible. It could revolutionize [solar power] very quickly if it’s successful.”

Lots of other nanoscientists around the world are working on different kinds of self-assembly. If they succeed, then self-assembly could eventually be used for making many other things, like the tiny electrical chips that run computers and iPods and radios. Self-assembly might allow scientists to make all of these things smaller than ever before. Years from now, an iPod might be the size of a dime.

These are the hopes of nanoscience, at least. Finding out whether they happen will take years of hard work. Scientists like Liang and Jung can look forward to spending a lot more time in their bunny suits.

POWER WORDS

Atom – The basic structure of a chemical element. Atoms have a nucleus that contains protons and neutrons and is surrounded by electrons that move around it in orbits at high speed. When atoms combine together they form molecules.

Bunny suit – A white suit that is worn in a clean room to prevent dirt and flakes of skin from interfering with experiments.

Chemical compound – A substance made of atoms of two or more chemical elements that are combined in molecules.

Chip – A complex electric circuit that is etched onto a tiny slice of material called a semiconductor. Chips are used in computers and most electronic devices and may contain tiny switches, capacitors and other devices.

Circuit – A closed path through which an electrical current flows. Circuits have a source of electricity, such as a battery or generator, and a wire that connects the source to a part that uses the electricity, such as a lamp or television.

Clean room – A room used in laboratory work that is kept virtually free of contaminants such as dust and bacteria.

Comet – A mass of ice, frozen gases, and dust particles that travels around the Sun in a long path.

Electricity – A form of energy produced by particles that have charge, especially electrons. Electricity can flow in an electric current, or it can be static.

Foundry – The building and works for casting metals.

Magnification – A number that shows how many times larger an object looks than it really is.

Microscope – An instrument that makes very small objects appear larger.

Electron microscope – A very powerful microscope that uses a beam of electrons, instead of light, to magnify objects that are too small to be seen with an ordinary microscope.

Molecule – A group of two or more atoms that are joined together by sharing electrons in a chemical bond.

Nanometer – One billionth of a meter.

Nanoscience – The study of things at the ultrasmall scale, usually a hundred nanometers or less.

Photovoltaic cell – A device that changes sunlight into electricity. Solar cells are used to supply power to satellites, calculators and other devices.

Printing press – A machine that uses contact to transfer letters or images onto paper.

Red blood cell – A cell that is shaped like a disk and is found in the blood of humans and other vertebrates.

Self-assembly – A process by which disorganized, disordered components create on their own some organized structure or pattern.

Silicon – A chemical element that makes up about one-fourth of the Earth’s crust.

Solar energy – Energy that comes from the sun’s radiation. Solar energy can heat up rooms that have windows facing the sun and can also be used to make electricity in solar cells.

Yeon Sik Jung puts chemicals onto a silicon wafer at start of an experiment in the clean room. Credit: D. Fox

Watching Yeon Sik Jung’s slow, careful movements, you sense that he’s doing something important. But it’s way too small to see.

Jung (pronounced Yoong) is dressed in white from head to toe. He wears a white jumpsuit, white boots, a white mask with goggles and a white cap on his head.

With a white-gloved hand, Jung lifts an eyedropper and squeezes liquid onto a flat, shiny disk. That glistening drop hides an invisible world. And Jung controls that world. Within, he is creating some of the smallest electric circuits ever made.

Jung works at Lawrence Berkeley National Laboratory’s Molecular Foundry, just outside Berkeley, Calif. A foundry is a place where tools and other parts are made out of metal. Molecules are tiny building blocks in everything from snot to snails to you and me. Put the two words together, and you have a place where scientists use molecules like Legos to build things too small to see.

Jung is currently working on an invention that could help us overcome the challenges of global warming. Another scientist, named Xiaogan Liang (pronounced Lie-Ang), stands nearby. The two scientists are trying to build tiny electrical circuits called solar photovoltaic cells within the drop of liquid. Solar cells can turn sunlight into electricity.

Filthy people

Jung, Liang and I have to wear these white suits, called “bunny suits,” because we’re in a special room called the clean room.

You may not realize it, but people are filthy—even after a bath. Your body constantly sheds flakes of dead skin. Your clothes, hair and shoes let specks of dust loose into the air. Every breath that you inhale contains more than 20,000 pieces of this invisible garbage, twirling around like loose leaves on a windy autumn day. That tiny trash doesn’t usually hurt your lungs, but it would ruin the work that Liang and Jung are trying to do.

Compared with the tiny things that Liang and Jung are building, a single flake of dandruff is huge. “A speck of dust would be like a comet,” says Liang, referring to the huge chunks of ice that fly through space. A comet hitting Earth could destroy a city, and a piece of dust landing in Jung’s little drop of liquid would ruin his miniature world, too.

So we have to cover our filthy selves in these suits. Pumps filter the air to remove any stray bits of dust. No eating or drinking is allowed. We’re not even supposed to fart. “In principle, it is not desirable to do that,” says Liang in a careful, scientific tone. “But we don’t have detectors in here.”

Every rooftop

As Liang talks, Jung lets the drop of liquid spread out on the shiny, mirror-like disk, called a wafer. Then he sets it in an oven heated to 200º Celsius. “That’s it,” says Jung through his mask. “We just need to wait a couple of hours.”

Today’s experiment is so simple that it’s almost boring to watch. But if Jung, Liang and other scientists succeed, their work could ultimately allow people to put solar photovoltaic cells on every rooftop in thousands of cities around the world, which would help reduce the amount of coal, oil and natural gas burned. That, in turn, would reduce the amount of Earth-warming carbon dioxide pumped into the air.

Xiaogan Liang works with the “focused ion beam” instrument in the clean room. Credit: D. Fox

For a long time, photovoltaic cells have been made from a mineral called silicon. To make pure silicon, scientists actually have to melt sand or rock. It means heating the rock to more than 1,000º C—pretty much what a volcano does. And then scientists have to heat the purified silicon again, to 600º C, so it will form pure crystals. “That takes a lot of energy, and energy costs money,” says Larry Kazmerski, an electrical engineer at the National Renewable Energy Laboratory in Golden, Colo. After that, expensive robotic machines have to build patterns onto the silicon. “The processing is very involved and complex.”

So even though photovoltaic cells could help people burn less coal, oil and natural gas, they cost so much that few can afford to buy them. Even today, 40 years after the first photovoltaic cells were invented, few roofs have them.

Nanoscience, the science of very small things, could solve that problem. The term “nano” means one billionth. The term “nanometer” means one billionth of a meter—or about one billionth the length of a baseball bat.

Greasy frying pan

Liang, Jung and other nanoscientists are coming up with a new way to build really small things without the need for such high heat and without the help of the expensive robots. The process is called “directed self-assembly,” and it’s surprisingly simple.

You mix a couple of chemicals together, put a drop of the liquid onto a piece of silicon or plastic (it doesn’t really matter what), and then those chemicals do the work for you. As the chemicals dry, the individual molecules arrange themselves into a complicated pattern, like the pattern that your grandmother might stitch on a quilt. For the photovoltaic cells, Liang and Jung want to create row after row of evenly spaced pencils that will stand up like spines on a porcupine.

If you’ve ever watched a frying pan full of grease cool off, then you’ve seen a very simple kind of self-assembly. As the pan cools, the grease forms little round droplets that sit on top the water in the pan. It happens automatically because of the way that grease and water molecules interact with each other.

Another kind of self-assembly happens when snow falls during winter. All by themselves, water molecules latch together to form beautiful, complicated six-pointed stars of ice — snowflakes. Snowflakes are so complicated that you could never cut a real one out of construction paper using scissors. And yet the mindless little molecules do it themselves.

So what if you could learn to make the molecules do what you want them to? What if you could mix two chemicals so the molecules arranged into specific shapes? What if you could control those patterns just by choosing one chemical or another? Depending on the chemicals you mixed, you might get a polka-dot pattern. Or perfectly straight pinstripes. Or spirals. Or a crisscrossed honeycomb, like in a beehive.

Liang, Jung and their boss at the Molecule Foundry (a scientist named Deirdre Olynick) are learning the art of self-assembly. They can create all of those patterns by choosing the chemicals to mix together. Today in the lab, Liang and Jung are making tiny pegs like pencils standing straight up. If it works correctly, each pencil will be exactly the same size, about one ten thousandth as wide as the sharp point of a safety pin.

Interlocking fingers

Solar cells are made of two types of material, one stacked on top of the other. When sunlight hits the cells, it knocks electrons from one layer into the other—creating electricity. (Electricity is the movement of these tiny charged electrons.) Those two layers could sit flat on top of each other, like layers in a birthday cake. But the solar cell works better if the two layers interlock. With an interlocking pattern, the two layers touch each other over more area. It gives the cells a better net for catching sunlight, and they can convert more of the sunlight into electricity. Those tiny pencils that Liang and Jung are making will be the first step in creating layers that interlock like fingers.

Self-assembly avoids the high temperatures used in making pure silicon. Never mind volcano temperatures reaching 1,000º C. Jung and Liang are cooking their drop of liquid at just 200º C—about as hot as pizza is cooked. And because the molecules arrange themselves, Jung and Liang also should not need as many expensive robotic machines to make the complicated patterns that will interlock the two layers in their solar cells.

Xiaogan Liang looks at the self-assembled projects under the electron microscope in the clean room. Credit: D. Fox

The big challenges in self-assembly are being clean and using the right recipe. And the recipe that Jung and Liang are using today is simpler than making pizza.

“That’s the point,” says Stefano Cabrini, the director of the Molecular Foundry. “The point of self-assembly is to make something easily that you can produce many, many of.”

Invisible forest

After waiting two hours for the chemicals to bake and dry, Liang and I slip back into our bunny suits and return to the clean room.

As Liang lifts the wafer with a pair of tweezers, it’s hard to see any difference. The wafer looks shiny, just like before. The coating of chemicals on the wafer is very thin—only one ten-thousandth as thick as a sheet of aluminum foil.

In order to see the pattern that those molecular Lego blocks have formed, we need to look at it through a special microscope, called an electron microscope. This microscope is the size of a small refrigerator, with wires coming out on all sides. The picture from the electron microscope shows on a computer screen.

As Liang turns knobs to focus the microscope, a hidden world takes shape.

On the screen we see what looks like a forest of gray pencils standing straight up. If we were looking at red blood cells or little amoebas swimming in pond water, we might need to magnify the picture only 200 times. But in order to see this hidden forest of pencils, Liang has magnified the picture 590,630 times.

Each one of those pencils is only 60 atoms across. Even the most advanced silicon-carving robots today cannot carve shapes this small. But here, the researchers have done it just by mixing a couple of chemicals together. Shake and bake.

Printing money

This pencil-studded wafer that Liang and Jung have made could someday be used to print solar cells onto sheets of plastic, the same way that dollar bills are printed onto paper.

In the factory, a sheet of plastic might roll off of a giant spool. As the sheet of plastic moves, like a conveyor belt, a huge printing press would squish down on it. That printing press would have the same tiny pencil-studded pattern that Liang and Jung made today. It would press that shape into the plastic—“like kids making handprints in the mud,” says Liang. Then another chemical could be painted over the top of the plastic sheet, filling the holes made by the tiny pencils in the printing press and creating a second layer. And abracadabra—you would have a sheet of photovoltaic cells. That sheet would be rolled like toilet paper onto another huge spool.

When people build a house, they could go to the store and buy a few rolls of that solar cell paper. They’d unroll the cells onto the roof of their houses. Unlike toilet papering a house, though, this would be good for the environment. Those solar cells would convert sunlight into the electricity needed to turn on lights and run computers.

If this self-assembly works, it could allow many more people around the world to put solar cells on their buildings. “There is risk. There’s no guarantee it will work,” says Kazmerski. “But the benefit is quite incredible. It could revolutionize [solar power] very quickly if it’s successful.”

Lots of other nanoscientists around the world are working on different kinds of self-assembly. If they succeed, then self-assembly could eventually be used for making many other things, like the tiny electrical chips that run computers and iPods and radios. Self-assembly might allow scientists to make all of these things smaller than ever before. Years from now, an iPod might be the size of a dime.

These are the hopes of nanoscience, at least. Finding out whether they happen will take years of hard work. Scientists like Liang and Jung can look forward to spending a lot more time in their bunny suits.

POWER WORDS

Atom – The basic structure of a chemical element. Atoms have a nucleus that contains protons and neutrons and is surrounded by electrons that move around it in orbits at high speed. When atoms combine together they form molecules.

Bunny suit – A white suit that is worn in a clean room to prevent dirt and flakes of skin from interfering with experiments.

Chemical compound – A substance made of atoms of two or more chemical elements that are combined in molecules.

Chip – A complex electric circuit that is etched onto a tiny slice of material called a semiconductor. Chips are used in computers and most electronic devices and may contain tiny switches, capacitors and other devices.

Circuit – A closed path through which an electrical current flows. Circuits have a source of electricity, such as a battery or generator, and a wire that connects the source to a part that uses the electricity, such as a lamp or television.

Clean room – A room used in laboratory work that is kept virtually free of contaminants such as dust and bacteria.

Comet – A mass of ice, frozen gases, and dust particles that travels around the Sun in a long path.

Electricity – A form of energy produced by particles that have charge, especially electrons. Electricity can flow in an electric current, or it can be static.

Foundry – The building and works for casting metals.

Magnification – A number that shows how many times larger an object looks than it really is.

Microscope – An instrument that makes very small objects appear larger.

Electron microscope – A very powerful microscope that uses a beam of electrons, instead of light, to magnify objects that are too small to be seen with an ordinary microscope.

Molecule – A group of two or more atoms that are joined together by sharing electrons in a chemical bond.

Nanometer – One billionth of a meter.

Nanoscience – The study of things at the ultrasmall scale, usually a hundred nanometers or less.

Photovoltaic cell – A device that changes sunlight into electricity. Solar cells are used to supply power to satellites, calculators and other devices.

Printing press – A machine that uses contact to transfer letters or images onto paper.

Red blood cell – A cell that is shaped like a disk and is found in the blood of humans and other vertebrates.

Self-assembly – A process by which disorganized, disordered components create on their own some organized structure or pattern.

Silicon – A chemical element that makes up about one-fourth of the Earth’s crust.

Solar energy – Energy that comes from the sun’s radiation. Solar energy can heat up rooms that have windows facing the sun and can also be used to make electricity in solar cells.

This stone core was drilled from an ancient seabed that now lies nearly 3 miles underground. The dark color comes from oil left behind by bacteria and animals that lived over 500 million years ago. The white color comes from salt left behind by the sea.

Gordon Love walked past the warm waters of the Arabian Sea as they lapped on a white sandy beach in the country of Oman. He entered a metal warehouse and walked past row after row of hallways lined with sliding metal doors. Some of these doors concealed an important piece of history.

Love, a geochemist now at the University of California, Riverside, had come to the Middle East to work for an oil company for a couple of weeks. But this trip would also give him a rare chance to look at rocks from deep inside the Earth. It would lead him and his partners to a major new discovery about early life on our planet.

Behind each one of the warehouse’s metal doors lay a cylinder of stone about the width and length of a baseball bat. You might call this warehouse a library of both rocks and history. These cylinders of stone — called cores — were drilled from the flat and dusty deserts of Oman by people looking for oil. The stone cores were lifted out of drill holes that reach three miles underground. Those drill holes pierced through layer after layer of petrified mud, which contained once-living material that turned into rock over time. This mud collected over millions of years on an ancient sea bed. You can see the layers as stripes of gray, white and brown stone in the cores. If you stacked these cores end to end they would run for miles — and they would tell the history of this ancient sea now buried beneath the desert.

Love entered a room where dozens of sections of core were laid out on tables. He could tell from the brown color of the stone that it still contained tiny bits of oil. That brown stone was just what he was looking for.

Scientist Gordon Love looked at molecular fossils in rocks as deep as 3 miles underground, similar to the dark ones shown here in the desert of Oman.

David Fike, Washington University

Molecular fossils

Oil doesn’t just fuel cars, trucks and airplanes. It also contains a record of the past. Oil contains chemical traces of things that lived hundreds of millions of years ago. Scientists call these chemicals “molecular fossils.” They can exist even when more obvious fossils, like the imprints of leaves or seashells pressed into rocks, do not survive the extreme heat and pressure of being buried deep in the Earth.

By studying the molecular fossils in the cores lifted from drill holes, Love and his colleague, Roger Summons of the Massachusetts Institute of Technology (MIT), have found evidence of animals that lived as long as 751 million years ago.

“At present it’s the oldest fossil evidence for animals,” says Love. In fact, it’s up to 176 million years older than any other animal fossils that scientists have found.

This 550 million-year-old fossil from Australia may be the oldest fossil imprint of a sponge.

James Gehling, South Australia Museum in Adelaide

The animals that Love found may have been some of the first on Earth. Human eyes have never seen these animals and have never even seen the faint shapes that they left pressed between rocks. The tortures of the deep Earth have long since erased those shapes. But by studying the invisible molecular fossils left behind by these animals, Love and Summons can not only tell that these creatures lived — they can actually make some guesses about what they looked like.

Greasy black tar

Oil forms over millions of years as dead plants, animals and bacteria are buried beneath sand or mud and decompose deep underground. Most of the grease seeps out of rocks and drains into spaces underground where it collects in large pools — the places where oil companies like to aim their drills. This oil in Oman is the oldest oil that companies have ever tried to drill out of the ground and turn into gasoline. This oil came from bacteria, algae and other critters that lived in an ocean over 500 million years ago.

The kind of molecular fossil left behind depends on the kind of organism decomposing. Bacterial molecular fossils look different from those fossils left behind by animals, for example. By studying such fossils, Summons and Love hoped to find out what kinds of things were living in the ocean when the rocks formed.

This adult sponge, about the size of a fist, was found in ankle-deep water in the Great Barrier Reef off Australia’s coast.

Sally Leys, University of Alberta, Edmonton)

In the warehouse that day, Love sawed some marble-sized chunks of rock out of the cores. The rock was as hard as cement. He took his little pieces of rock back to Summons’ lab in Cambridge, and crushed them into dust. He cooked the dust in acid until he was left with a glob of greasy black tar — the remains of ancient dead things.

Love spent another two weeks purifying, or removing unwanted material from, this tar until he held in his hand a test tube of colorless liquid. That liquid contained the molecular fossils that he and Summons wanted to analyze. The molecular fossils were invisible to the eye. A person might not even taste the small amounts of them in the tube. But Love could detect the fossils using a refrigerator-sized machine called a GC-MS, or gas chromatograph mass spectrometer.

Love loaded a few drops of the liquid into the GC-MS and watched the computer screen as the machine analyzed the dozens of chemicals.

Shown is the larva, or young, of the same species of sponge pictured as an adult. About the size of a grain of salt, this tiny creature was seen through an electron microscope.

Sally Leys, University of Alberta, Edmonton)

Blobby sponges

If you’ve ever been in a hospital or seen a hospital show on TV, then maybe you’ve seen the bright line that moves across a heart monitor, tracing out jagged peaks and dips every time a person’s heart beats. Love saw something like this as he watched the GC-MS analyze the molecular fossils. A line running across the computer screen traced out a sharp spike every time the machine detected another chemical.

As Love sat and watched, one of those spikes grabbed his attention: It stood for a chemical called 24-isopropylcholestane, or 24-ipc. Love had seen 24-ipc in rocks before — it’s a well-known chemical — but seeing it in these old rocks from Oman was a big deal.

Scientists consider 24-ipc to be a molecular fossil that comes from animals called sea sponges. Scientists have looked at various animals, fungi and bacteria that live on Earth today to see which chemicals they produce. Researchers have found that sponges produce large amounts of a chemical closely related to 24-ipc. During heating, such as that deep inside the Earth, this chemical slowly changes into 24-ipc. “Sponges are the only organisms that produce it in any significant quantities,” says Love.

Sea sponges are cigar- or balloon-shaped animals that sit on the seafloor. They eat by filtering bacteria and other tiny organisms out of the water. You wouldn’t exactly call sea sponges smart. They have no brains, no eyes, no legs and no fins. They’re some of the simplest animals on Earth. Some biologists think sponges were the first animals to evolve, or develop from simpler, single-celled organisms through a process of gradual change over millions of years. So when Love saw 24-ipc in the oil from these old rocks, he knew it was important.

The oldest known sea sponge fossils that you can see with the naked eye are cup-shaped imprints found in 550-million-year-old rocks. Scientists have also seen blobby imprints, like round, quilted pillows, in rocks as old as 575 million years. (Though some scientists believe that many of these older animal fossils aren’t related to modern animals.) Researchers think these imprints were probably made by some kind of animal — although the blobs are so strange, they don’t know what kind of animal. But the molecular sponge fossils that Love had just found were much older than any of those shapes in the rocks. Judging from the age of the rocks from Oman he tested, these sea sponges are at least 635 million years old, and maybe as much as 751 million years old.

A big disagreement

These findings by Love, Summons, David Fike of Washington University in St. Louis, and nine other scientists will be published on February 5 in a major scientific journal called Nature. Their discovery has a lot of people excited. These new molecular fossils may help to solve a big disagreement about the earliest animals on Earth.

In other studies, biologists have compared the DNA, a molecule that holds an organism’s genetic information, of different animals alive today, such as sponges, clams, insects, worms, mice and humans. Scientists have done this in order to estimate how long ago the first animals lived. These “molecular clock” calculations say that the first animals evolved somewhere between 650 and 950 million years ago. And yet the oldest fossil imprints of animals are only 575 million years old.

That disagreement between the dates from the fossil imprints and the dates from the molecular clocks caused some scientists to wonder whether the molecular clock calculations were wrong. But by showing molecular fossils of animals maybe as old as 751 million years, Summons and Love’s new findings have something to say about that disagreement. “I think this new work is both important and believable,” says Andrew Knoll, a paleontologist who studies early fossils at Harvard University. “This goes a long way toward reconciling the geologic record with molecular clock estimates.”

Swimming in the early oceans

It makes sense that the first animals might have been sponges or something like them. All animals, whether they live in water or on land, need to breathe oxygen; without it, they suffocate. But 600 or 700 million years ago the Earth hadn’t yet filled up with oxygen the way it has today. The oceans probably contained oxygen in their shallowest parts, but the deeper waters likely contained hardly any oxygen.

This is one reason why it makes sense that sponges are the first animals, says Kevin Peterson of Dartmouth College in Hanover, N.H. “Sponges have exceedingly low metabolism,” he says, meaning that some kinds of sponges consume oxygen slowly compared to other animals, and so such sponges can tolerate lower levels of oxygen.

Even if these ancient animals were closely related to modern-day sponges, Knoll isn’t willing to say whether these early animals actually looked like the same big cigar-shaped sponges that we see in our oceans today.

It’s true that adult sponges are big balloons which sit on the sea floor and suck food out of the water. But young sponges, called larvae, look very different. They are tiny — about the size of a grain of sand. And rather than sitting on the ocean bottom, they swim through the water by whipping around tiny oars on their body that look like hairs.

The animals that Love detected could have looked more like tiny larvae than big adult sponges. “If you had been swimming in the same ocean, you might not have noticed them,” says Knoll.

Going Deeper:

News Detective: Hunting for oil and fossils

Questions about the article

Word Find: Invisible Fossils