When nobody else wanted the job, Marguerite Vogt stepped in.

Working from early morning until late at night in a small, isolated basement laboratory at the California Institute of Technology, Vogt painstakingly handled test tubes and petri dishes under a fume hood: incubating, pipetting, centrifuging, incubating again. She was trying to grow a dangerous pathogen: poliovirus.

It was 1952 and polio was one of the most feared diseases in America, paralyzing more than 15,000 people, mostly children, each year. Parents wouldn’t let their children play outside, and quarantines were instituted in neighborhoods with polio cases.

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Scientists were desperate for information about the virus, but many were hesitant to work with the infectious agent. “Everybody was afraid to go to that little lab in the basement,” says Martin Haas, professor of biology and oncology at the University of California, San Diego, and a personal friend and collaborator of Vogt’s for over three decades.

Vogt, a brand-new research associate in the laboratory of Renato Dulbecco, took on the task of attempting to grow and isolate the virus on a layer of monkey kidney cells. The method was called a plaque assay for the distinctive round plaques that form when a single virus particle kills all the cells around it.

Vogt didn’t tell her parents, both acclaimed scientists in Germany, that she was working with the virus. She later remarked that her father would have been very angry had he known of her poliovirus work, Haas says.

After a year of persistence, Vogt succeeded (and remained virus-free). In 1954, she and Dulbecco published the method for purifying and counting poliovirus particles. It was immediately used by other scientists to study variants of poliovirus, and by microbiologist Albert Sabin to identify and isolate strains of weakened poliovirus to make the oral polio vaccine used in mass vaccination campaigns around the world.

Perhaps even more importantly, the poliovirus plaque assay enabled scientists worldwide to analyze animal viruses at the level of individual cells, a field now known as molecular virology. Vogt and Dulbecco’s approach remains the gold standard for purifying and counting virus particles, including in recent studies of SARS-CoV-2, the virus that causes COVID-19. The method, used to measure how infectious a virus is and isolate strains of a virus for further research, is ubiquitous in labs around the world.

Throughout a career spanning three-quarters of a century, beginning with a publication when she was 14 years old, Vogt contributed extensively to our knowledge of the genetics of animal development, how viruses can cause cancer and cellular life cycles. Upon her death in 2007 at the age of 94, nearly 100 three-ring binders lined the shelves of her office, filled with notes on decades of experiments.

Vogt was known for her intense, inventive lab work, including what others have called her “green thumb” for tissue culture — the process of growing cells, viruses and tissues in a dish.

“Being a meticulous person, she worried about every detail of the process of cell culture,” says David Baltimore, biologist and president emeritus of Caltech who worked for three years in a lab close to Dulbecco’s. “That’s really important, because it is finicky. Long experience and precise handling are key to getting good data.”

Born in 1913, Vogt grew up in Germany surrounded by science. The younger daughter of two pioneers of brain research, Oskar and Cécile Vogt, she and her sister Marthe were budding scientists from their youth. Marguerite Vogt’s first paper, published in 1927, investigated the genetics of fruit fly development.

But a year after receiving her M.D. at the Friedrich Wilhelm University in 1936, Vogt and her liberal family were ousted from Berlin by the Nazis. Her parents lost their positions at the Kaiser Wilhelm Institute for Brain Research (now the Max Planck Institute), and Oskar was accused of supporting communists. The family avoided arrest or death due to the intercession of the Krupp family, former patients of Oskar’s and well-connected arms manufacturers who supplied the Nazi regime. With funding from the Krupps, Oskar and Cécile set up a private brain research institute in a remote part of Germany’s Black Forest. There, they continued their research and offered shelter and jobs to other people fleeing Nazi persecution.

From her parents’ institute in the Black Forest, Vogt published 39 seminal papers on how hormones and genetics influence the development of fruit flies, work that was later considered ahead of its time. In 1950, with the help of German-American scientists Hermann Muller and Max Delbrück, Vogt emigrated from Germany to the United States. Vogt rarely talked about her experiences during World War II. She never returned to Germany and refused to speak her native tongue with visiting German students and scientists.

After briefly working with Delbrück on bacterial genetics, Vogt went to work for Dulbecco on the poliovirus assay in 1952. After that success, the pair investigated the role of viruses in cancer. Once again, Vogt developed a technique to grow a virus — this time a small DNA-containing virus called polyomavirus — and the pair was able to count how many cells the virus transformed into cancer cells. In subsequent papers, the team demonstrated that certain viruses integrate their genetic material into host cell DNA, causing uncontrolled cell growth. The discovery changed the way scientists and doctors thought about cancer, showing that cancer is caused by genetic changes in a cell.

In 1963, Vogt followed Dulbecco to the Salk Institute in La Jolla, Calif. There, she spent decades studying viruses that can cause tumors, as well as other areas that sparked her interest, such as trying to define a cellular clock. “She was not only very intense, she was very inventive,” says Haas. “She always knew which way to go and what do to.”

Like the early days studying poliovirus, Vogt worked long and hard, typically six days a week, 10 hours per day. “She liked trying new things, so we often tried to do techniques that she had admired in papers she had read, or we learned things from other labs,” says Candy Haggblom, Vogt’s laboratory assistant for the last 30 years of Vogt’s career.

Vogt never married or had children. “Science was my milk,” she told the New York Times in 2001. But Vogt didn’t lack for company: She was a friend and mentor to many of the young scientists in the lab, four of whom went on to earn Nobel Prizes, and as an accomplished pianist and cellist, Vogt hosted a chamber music group that met at her home every Sunday morning for over 40 years, Haas says.

In 1975, Dulbecco was awarded the Nobel Prize in physiology or medicine for work on how tumor viruses transform cells, a prize shared with Baltimore and virologist Howard Temin. Vogt was not recognized, and Dulbecco did not acknowledge her in his Nobel lecture.

During her lifetime, Vogt did not receive a single major prize or recognition. Despite an advanced degree and prestigious publication record, Vogt did not become a professor or get her own lab at Salk until after Dulbecco left the institute in 1972. She was 59 years old. That rankled her, says Haas, who cared for Vogt later in her life and thought of her like a mother. “She ran his lab while he ran around the world giving talks,” he says. “Marguerite ran it all.”

At 80, Vogt regularly jogged into the lab early in the morning. At 85, she published her final paper, fittingly about how human cells slow down and lose their ability to replicate with age.

Discoveries in a Moroccan cave have provided a rare look at how Stone Age people may have turned animal skins into clothing.

Bone tools, including hide scrapers and stone-tool sharpeners, were unearthed in Morocco’s Contrebandiers cave, say archaeologist Emily Hallett and colleagues. Dating of sediment, burned stones and animal teeth excavated there shows that the tools are around 90,000 to 120,000 years old, the scientists report September 16 in iScience.

“Prior to major successful dispersals out of Africa and into Eurasia, Homo sapiens [were] making tools for various specialized functions, and those behaviors would have aided them [in] new environments,” says Hallett, of the Max Planck Institute for the Science of Human History in Jena, Germany. Different types of bone tools from around the time of the Moroccan finds have been unearthed at a handful of other African sites, though uses for many of those items remain unclear. Researchers have largely focused on an explosion of African bone tool styles that appeared around 44,000 years ago, after human expansions into Eurasia.

Of 62 bone implements from the cave, seven were hide scrapers. These tools were crafted from pieces of antelope or wild cattle ribs that were split in half lengthwise and worked into a flat, spatula-like shape. Short, deep grooves and polish on these items resulted from scraping animal hides, the researchers say.

The team unearthed the tools along with skinned animals’ bones. Patterns of stone-tool incisions on limb and jaw bones of sand foxes, golden jackals and wildcats resulted from detaching skin at the paws and pulling it over the head in one piece, providing evidence for the way the bone hide scrapers were used, the scientists say.

Ancient humans could have put hides presumably worked into leather or pelts to various uses, though clothing seems especially likely, Hallett says. DNA evidence of body lice origins suggests that people began wearing clothes at least 190,000 years ago (SN: 4/20/10).

Fossilized footprints found on a beach in southern Spain betray what may have been a nursery for an extinct species of elephant.

The track-rich coastal site, which scientists have dubbed the Matalascañas Trampled Surface, is typically covered by 1½ meters of sand, says Clive Finlayson, an evolutionary biologist at the Gibraltar National Museum. But storm surges in the spring of 2020 washed away much of that sand and exposed the preserved footprints of ancient elephants, cattle, deer, pigs, wolves, water birds and even Neandertals, Finlayson and colleagues report September 16 in Scientific Reports. The sandy-clay sediments hosting this trove of tracks were probably laid down about 106,000 years ago, previous studies suggest.

Among the newly uncovered tracks are the first-of-their-kind footprints of newborn straight-tusked elephants (Palaeoloxodon antiquus), an extinct species that probably died out during the last ice age (SN: 6/13/17). The teeny tracks — which measure 9.6 centimeters across, about the size of a drink coaster — suggest that the petite, possibly 2-month-old pachyderms stood about 66 centimeters tall at their shoulders and weighed around 70 kilograms, slightly heftier than a Newfoundland dog.

Based on previous finds elsewhere of actual bones, adult straight-tusked elephants may have weighed 5.5 metric tons for females and a whopping 13 tons for males.

The mix of elephant tracks at the site suggests that family groups including newborns, juveniles and adult females frequented the area and possibly used it as a nursery, the researchers say. Other fossils found at the site, including those preserving traces of ancient roots, hint that the area was rich in vegetation and speckled with lakes and ponds.

The team’s findings “are a thrilling study,” says Anthony Martin, a trace fossil expert at Emory University in Atlanta who wasn’t involved in the research. Series of footprints show how the ancient elephants were moving, offer insight into their social structure and even provide a glimpse of their reproductive ecology, he says. If newborns were part of the family group and “if they were acting anything like modern elephants, the mother had to be nearby,” Martin says.

What’s more, the presence of preserved Neandertal footprints at the site suggests that the ancient hominids foraged there and may have preyed upon young elephants or scavenged dead elephants or other creatures, Martin says. The Neandertals “probably were not foolhardy enough to take on a full-sized elephant.”

Over a decade ago, behavioral ecologist Diane Colombelli-Négrel was wiring superb fairy wrens’ nests to record the birds’ sounds when she noticed something odd. Mother fairy wrens sang while incubating their eggs, even though it would have made more sense to keep quiet to avoid attracting predators.

The discovery “was a bit of an accident,” says Colombelli-Négrel, of Flinders University in Adelaide, Australia. And it made her wonder: Could the baby birds be learning sounds, or perhaps even songs, even before they hatch?

Scientists have long wondered how early in development individuals learn to perceive distinct sounds. It’s known that human fetuses learn to recognize their mother’s voice (SN: 1/7/13). For birds such as superb fairy wrens (Malurus cyaneus) that perfect their songs with parental tutoring, it was thought that sound perception began well after hatching. But when it became obvious that mother birds were intentionally singing to their eggs, “we knew we were on to something,” says avian ecologist Sonia Kleindorfer of the University of Vienna.

Previous research by Colombelli-Négrel, Kleindorfer and colleagues showed that unhatched superb fairy wrens learn a vocal “password” from mom that helps mothers discriminate their own nestlings from those of pesky cuckoo invaders (SN: 5/9/14). What’s more, unhatched superb fairy wrens appear to distinguish between songs of their own species and others, the team reported in 2014.

That ability extends beyond superb fairy wrens, new research suggests. At least four additional types of birds recognize sounds specific to their species while still in their eggs, the researchers report in the Oct. 25 Philosophical Transactions of the Royal Society B.

The finding is a surprise to many birdsong scientists, says vocal learning neuroscientist Wan-chun Liu of Colgate University in Hamilton, N.Y., who wasn’t involved in the new research. “We used to think a lot of the learning happened after hatching, but now there seems to be more and more evidence suggesting, even in the embryonic stage … they are listening,” he says.

In birds and humans, a drop in embryonic heart rate is known to indicate attention to a stimulus. Colombelli-Négrel and colleagues’ earlier studies of unhatched fairy wrens showed a slowed heart rate in response to repeated sounds of their own species, but not others.

To investigate whether this phenomenon is widespread among birds, the team turned their attention to the embryonic heartbeats of captive Japanese quail (Coturnix japonica domestica), plus three more wild species: little penguins (Eudyptula minor), red-winged fairy wrens (Malurus elegans) and Darwin’s small ground finches (Geospiza fuliginosa).

The team temporarily removed 109 eggs from nests and measured the heart rates of unhatched chicks before, during and after exposure to playbacks of songs from their own species or others. And the researchers investigated whether 138 individual embryos became habituated to repeated sounds of unfamiliar individuals singing their species’ own songs, which would imply learning had occurred.

“We expected to find learning evidence in the songbirds but not in the quail and penguins,” Colombelli-Négrel says. That’s because penguins and quail are “vocal nonlearners” — birds thought to have calls that are genetically programmed from birth and not learned from a tutor.

To the researchers’ surprise, all of the embryos showed not only a slowed heart rate in response to repeated sounds of their own species, but also habituation. That finding suggests that these birds learn to perceive the sounds of their species-specific songs embryonically.

The scientists don’t know why the penguins and quail, which have their own calls genetically baked in, have the ability to distinguish their own species’ calls from those of other birds right from birth. Perhaps it’s useful for survival, the researchers speculate.

“Birds are like humans in that there is mother- or father-offspring communication even before birth,” says coauthor Mark Hauber, a neurobiologist at the University of Illinois at Urbana-Champaign. The team hopes to study prenatal sound perception in even more bird species to probe the advantages of this early egg-u-cation.

The severe, devastating wildfires that raged across southeastern Australia in late 2019 and early 2020 packed a powerful punch that extended far beyond the country, two new studies find.

The blazes injected at least twice as much carbon dioxide into the atmosphere as was previously thought, one team’s satellite-derived estimates revealed. The fires also sent up vast clouds of smoke and ash that wafted far to the east over the Southern Ocean, fertilizing the waters with nutrients and triggering widespread blooms of microscopic marine algae called phytoplankton, another team found. Both studies were published online September 15 in Nature.

Meteorologist Ivar van der Velde of the SRON Netherlands Institute for Space Research in Leiden and colleagues first examined carbon monoxide data collected over southeastern Australia by the satellite-based instrument TROPOMI from November 2019 to January 2020, during the worst of the fires. Then, to get new estimates of the carbon dioxide emissions attributable to the fires, the team used previously determined ratios of carbon monoxide to carbon dioxide emitted by the region’s eucalyptus forests — the predominant type of forest that was scorched in the blazes — during earlier wildfires and prescribed burns.

Van der Velde’s team estimates that the fires released from 517 trillion to 867 trillion grams of carbon dioxide to the atmosphere. “The sheer magnitude of CO₂ that was emitted to the atmosphere … was much larger than what we initially thought it would be,” van der Velde says. The emissions “from this single event were significantly higher than what all Australians normally emit with the combustion of fossil fuels in an entire year.”

Previous assessments of CO₂ emissions from the fires, based on estimations of burned area and biomass consumed by the blazes, calculated an average of about 275 trillion grams. Using the satellite-derived carbon monoxide data, the researchers say, dramatically improves the ability to distinguish actual emissions from the fires from other background sources of the gases, giving a more accurate assessment.

That finding has worrisome implications. The fires swiftly cut a swath through southeastern Australia’s eucalyptus forests, devastating the forests to a degree that made their rapid recovery more difficult — which in turn affects how much carbon the trees can sequester, van der Velde says (SN: 3/9/21). Fires in northern and central Australia’s dry, grassy savannas are seen as more climate neutral because the grasses can regrow more quickly, he says.

And severe fire seasons are likely to become more common in southeastern Australia with ongoing climate change. Climate change has already increased the likelihood of severe fire events such as the 2019–2020 fire season by at least 30 percent (SN: 3/4/20).

The smoke and ash from the fires also packed a powerful punch. Scientists watched in awe as the fires created a “super outbreak” of towering thunderclouds from December 29 to December 31 in 2019 (SN: 12/15/20). These clouds spewed tiny aerosol particles of ash and smoke high into the stratosphere.

Aerosols from the fires also traveled eastward through the lower atmosphere, ultimately reaching the Southern Ocean where they triggered blooms of phytoplankton in its iron-starved waters. Geochemist Weiyi Tang, now at Princeton University, and colleagues analyzed aerosols from the fires and found the particles to be rich in iron, an important nutrient for the algae. By tracing the atmospheric paths of the cloud of ash and smoke across the ocean, the team was able to link the observed blooms — huge patches of chlorophyll detected by satellite — to the fires.

Researchers have long thought that fires can trigger ocean blooms, particularly in the Southern Ocean, under the right conditions, says marine biogeochemist Joan Llort, now at the Barcelona Supercomputing Center and a coauthor on the study. But this research marks the most direct observation ever made of such an event — in part because it was such a massive one, Llort says.

Large ocean blooms are “yet another process which is potentially being modified by climate change,” says biogeochemist Nicolas Cassar of Duke University, also a coauthor on the study.

One of the big questions to emerge from the study, Cassar adds, is just how much carbon these phytoplankton may have ultimately removed from the atmosphere as they bloomed. Some of the carbon that the algae draw out of the air through photosynthesis sinks with them to the seafloor as they die. But some of it is quickly respired back to the atmosphere, muting any mitigating effect that the blooms might have on the wildfire emissions. To really assess what role the algae play, he says, would require a rapid-response team aboard an ocean vessel that could measure these chemical processes as they are happening.

The sheer size of this wildfire-triggered bloom — “larger than Australia itself” — shows that “wildfires have the potential to increase marine productivity by very large amounts,” says Douglas Hamilton, a climate scientist at Cornell University who was not connected with the study.

“The impact of fires on society is not straightforward,” Hamilton adds. The same smoke that can cause severe health impacts when inhaled “is also supplying nutrients to ecosystems and helping support marine food webs.” What this study demonstrates, he adds, is that to understand how future increases in fire activity might help shape the future of marine productivity “it is crucial that we monitor the impacts closely now.”

In The Descent of Man, published in 1871, Charles Darwin hypothesized that our ancestors came from Africa. He pointed out that among all animals, the African apes — gorillas and chimpanzees — were the most similar to humans. But he had little fossil evidence. The few known human fossils had been found in Europe, and those that trickled in over the next 50 years came from Europe and from Asia.

Had Darwin picked the wrong continent?

Finally, in 1924, a fortuitous find supported Darwin’s speculation. Among the debris at a limestone quarry in South Africa, miners recovered the fossilized skull of a toddler. Based on the child’s blend of humanlike and apelike features, an anatomist determined that the fossil was what was then popularly known as a “missing link.” It was the most apelike fossil yet found of a hominid — that is, a member of the family Hominidae, which includes modern humans and all our close, extinct relatives.

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That fossil wasn’t enough to confirm Africa as our homeland. Since that discovery, paleoanthropologists have amassed many thousands of fossils, and the evidence over and over again has pointed to Africa as our place of origin. Genetic studies reinforce that story. African apes are indeed our closest living relatives, with chimpanzees more closely related to us than to gorillas. In fact, many scientists now include great apes in the hominid family, using the narrower term “hominin” to refer to humans and our extinct cousins.

In a field with a reputation for bitter feuds and rivalries, the notion of humankind’s African origins unifies human evolution researchers. “I think everybody agrees and understands that Africa was very pivotal in the evolution of our species,” says Charles Musiba, a paleoanthropologist at the University of Colorado Denver.

Paleoanthropologists have sketched a rough timeline of how that evolution played out. Sometime between 9 million and 6 million years ago, the first hominins evolved. Walking upright on two legs distinguished our ancestors from other apes; our ancestors also had smaller canine teeth, perhaps a sign of less aggression and a change in social interactions. Between about 3.5 million and 3 million years ago, humankind’s forerunners ventured beyond wooded areas. Africa was growing drier, and grasslands spread across the continent. Hominins were also crafting stone tools by this time. The human genus, Homo, arrived between 2.5 million and 2 million years ago, maybe earlier, with larger brains than their predecessors. By at least 2 million years ago, Homo members started traveling from Africa to Eurasia. By about 300,000 years ago, Homo sapiens, our species, emerged.

But human evolution was not a gradual, linear process, as it appeared to be in the 1940s and ’50s. It did not consist of a nearly unbroken chain, one hominin evolving into the next through time. Fossil discoveries in the ’60s and ’70s revealed a bushier family tree, with many dead-end branches. By some counts, more than 20 hominin species have been identified in the fossil record. Experts disagree on how to classify all of these forms — “Fossil species are mental constructs,” a paleoanthropologist once told Science News — but clearly, hominins were diverse, with some species overlapping in both time and place.

Even our species wasn’t always alone. Just 50,000 years ago, the diminutive, 1-meter-tall Homo floresiensis, nicknamed the hobbit, lived on the Indonesian island of Flores. And 300,000 years ago, Homo naledi was a neighbor in South Africa.

Finding such “primitive” species — both had relatively small brains — living at the same time as H. sapiens was a big surprise, says Bernard Wood, a paleoanthropologist at George Washington University in Washington, D.C. Those discoveries, made within the last two decades, were reminders of how much is left to learn.

It’s premature to pen a comprehensive explanation of human evolution with so much ground — in Africa and elsewhere — to explore, Wood says. Our origin story is still a work in progress.

Eyes on Africa

Raymond Dart had a wedding to host.

It was a November afternoon in 1924, and the Australian-born anatomist was partially dressed in formal wear when he was distracted by fossils. Rocks containing the finds had just been brought to his home in Johannesburg, South Africa, from a mine near the town of Taung.

Imprinted on a knobby rock about as big as an orange were the folds, furrows and even blood vessels of a brain. It fit perfectly inside another rock that had a bit of jaw peeking out.

The groom pressed Dart to get back on track. “My god, Ray,” he said. “You’ve got to finish dressing immediately — or I’ll have to find another best man.”

As soon as the festivities ended, Dart, 31 years old at the time, started removing the jaw from its limestone casing, chipping away with knitting needles. A few weeks later, he had liberated not just a jaw but a partial skull preserving the face of a child.

On February 7, 1925, in the journal Nature, Dart introduced the Taung Child to the world. He described the fossil as an ape like no other, one with some distinctly humanlike features, including a relatively flat face and fairly small canine teeth. The foramen magnum, the hole through which the spinal cord exits the head, was positioned directly under the skull, implying the child had an erect posture and walked on two legs.

Dart concluded that the Taung Child belonged to “an extinct race of apes intermediate between living anthropoids and man.” His italicized text emphasized his judgment: The fossil was a so-called missing link between other primates and humans. He named it Australopithecus africanus, or southern ape of Africa.

The Taung Child was the second hominin fossil discovered in Africa, and much more primitive than the first. Dart argued that the find vindicated Darwin’s belief that humans arose on that continent. “There seems to be little doubt,” Science News Letter, the predecessor of Science News, reported, “that there has been discovered on the reputed ‘dark’ continent a most important step in the evolutionary history of man.”

But Dart’s claims were mostly met with skepticism. It would take more than two decades of new fossil finds and advances in geologic dating for Dart to be vindicated — and for Africa to become the epicenter of paleoanthropology.

Hot spots

This map marks locations of some of human evolution’s biggest fossil discoveries. The search in Africa began in the 1920s. Yet there is still much of the continent left to explore, as paleoanthropologists have mostly focused on eastern and southern Africa.

A. The oldest known Homo sapiens fossils, dating to about 300,000 years ago, come from Jebel Irhoud in Morocco.

B. At the Toros-Menalla site in Chad, scientists found what may be the earliest known hominin, Sahelanthropus tchadensis.

C. Ethiopia’s Afar region hosts numerous sites, some stretching back more than 5 million years. Major finds include the early hominin Ardipithecus and Lucy.

D. Southern Ethiopia and northern Kenya hold a long hominin history, including Australopithecus fossils, some of the oldest known stone tools, early Homo fossils and early H. sapiens fossils.

E. Louis and Mary Leakey put Tanzania’s Olduvai Gorge on the map with discoveries of Paranthropus boisei and Homo habilis. The nearby Laetoli site preserves hominin footprints dating to 3.6 million years ago.

F. The Kabwe skull, the first hominin fossil found in Africa, came from a mine in Zambia in 1921.

G. South Africa’s limestone caves have yielded Australopithecus, Paranthropus and Homo fossils.

H. Quarry workers near Taung, South Africa, recovered the first Australopithecus fossil ever found.

I. At caves along coastal South Africa, scientists have recovered a rich record of H. sapiens activity, including what may be the earliest known drawing and other signs of symbolic behavior.

Source: National Research Council/Understanding Climate’s Influence on Human Evolution 2010; Adapted by E. Otwell

Against the establishment

Unlike Darwin, many evolutionists of the late 19th and early 20th centuries had theorized that the human family tree was rooted in Asia. Some argued that Asia’s gibbons were our closest living relatives. Others reasoned that tectonic activity and climate change in Central Asia sparked human evolution. One naturalist even proposed that human origins traced back to a lost continent that had sunk in the Indian Ocean, forcing our ancestors to relocate to Southeast Asia.

And that’s where the best contender for an early human ancestor had been found. In the 1890s, a crew led by Dutch physician-turned-anthropologist Eugène Dubois had uncovered a skullcap and thigh bone on the Indonesian island of Java. The thick skullcap had heavy brow ridges, but Dubois estimated it once held a brain that was about twice as big as an ape’s and approaching the size of a human’s. The thigh bone indicated that this Java Man, later named Homo erectus, walked upright.

Europe had its own tantalizing fossils. Neandertals had been known since the mid-19th century, but by the early 20th century, they were generally thought to be cousins that lived too recently to shed much light on our early evolution. A more relevant discovery seemed to come in 1912, when an amateur archaeologist had recovered humanlike bones from near Piltdown, England; the site also contained fossils of extinct creatures, suggesting Piltdown Man was of great antiquity. Skull bones hinted he had a human-sized brain, but his primitive jaw had a large, apelike canine tooth.

Some experts questioned whether the skull and jaw belonged together. But British scientists embraced the discovery — and not just because it implied England had a role in human origins. Piltdown Man’s features fit with the British establishment’s view of human evolution, in which a big brain was the first trait to distinguish human ancestors from other apes.

So when Dart announced that he had found a small-brained bipedal ape with humanlike teeth in the southern tip of Africa, scientists were primed to be skeptical, says Paige Madison, a historian of science at the Natural History Museum of Denmark in Copenhagen. Scientists were also skeptical of Dart. While a student in London, he had earned a reputation as a “scientific heretic, given to sweeping claims,” according to a paper coauthored by a colleague.

But initial criticism focused mostly on practical concerns, says Madison, who has studied the skeptics’ reactions. “I found what they were actually saying on paper to be quite reasonable.”

A big problem: Dart’s fossil was of a 3- or 4-year-old child. Critics pointed out that a young ape tends to resemble humans in some ways, but the similarities disappear as the ape matures. Critics also complained that Dart hadn’t done proper comparative analyses with young chimps and gorillas, and he refused to send the fossil to England where such analyses could be done. This refusal irked the British old guard. “It was unpalatable to the scientists in England that the young colonial upstart had presumed to describe the skull himself,” one of Dart’s contemporaries later wrote, “instead of submitting it to his elders and betters.”

It’s hard not to wonder how the era’s colonialist and racist attitudes shaped perceptions. The Taung Child came to light at a time when eugenics was still considered legitimate science, and much of anthropology was devoted to categorizing people into races and arranging them into hierarchies. On the one hand, Western researchers tended to maintain the perverse notion that Africans are more primitive than other people, even less evolved. On the other, they wanted to believe Europe or Asia is where humans originated.

How these views influenced reactions to the Taung Child is not clear-cut. Many skeptics didn’t cite the fossil’s location as a problem, and some acknowledged humans could have evolved in Africa. But deep-seated biases may have made it easier for some researchers to reject the Taung Child and accept Piltdown Man, even though fossil evidence for that claim was also scant, says Sheela Athreya, a paleoanthropologist at Texas A&M University in College Station.

Newspapers worldwide followed the Taung Child controversy. And while fans sent Dart poems and short stories casting the child as a national hero, he also received letters from disapproving creationists.

Amid it all, Dart had convinced at least one well-known scientist. Robert Broom, a Scottish-born physician living in South Africa and an authority on reptile evolution, recognized that fossils of fully grown A. africanus individuals would be needed to confirm that the Taung Child’s humanlike qualities were retained in adulthood.

Broom began to find just that evidence in 1936 in caves not far from Johannesburg. Often taking the heavy-handed approach of detonating dynamite to free specimens, he amassed a collection of fossils representing both the young and the old. Limb, spine and hip bones confirmed South Africa was once home to a bipedal ape, and skull bones verified Dart’s inferences about A. africanus’ humanlike teeth.

Even the staunchest Dart doubters couldn’t overlook this evidence. British anatomist Arthur Keith, who had once called Dart’s assertions “preposterous,” conceded. “I am now convinced,” he wrote in a one-paragraph letter to Nature in 1947, “that Prof. Dart was right and that I was wrong; the Australopithecinae are in or near the line which culminated in the human form.”

A few years later, in 1953, researchers exposed Piltdown Man to be a hoax — someone had planted a modern human skull alongside an orangutan jaw with its teeth filed down. Many experts outside of England had never been convinced by the find in the first place. “It was not a complete surprise when he was proved to be a fake,” Science News Letter reported.

Still, Africa’s role in human evolution was not cemented. From the time of the Taung Child’s unearthing through World War II, discoveries of hominin fossils continued in Indonesia and at a cave site near Beijing called Zhoukoudian. These fossils kept the focus on Asia.

A series of surprises

It was ultimately a series of discoveries by the husband-wife paleoanthropologists Louis and Mary Leakey that shifted the focus. Louis, who had grown up in East Africa as the son of English missionaries, had long believed Africa was the human homeland. While Broom was scouring South Africa in the 1930s, the Leakeys began exploring Olduvai Gorge in what is now Tanzania.

Year after year, the pair failed to find hominin fossils. But they dug up stone tools, suggesting that hominins must have lived there. So they kept looking. One day in 1959, while an ill Louis stayed behind in camp, Mary discovered a skull with small canine teeth like Australopithecus. But the fossil’s giant molar teeth, flaring cheekbones and bony crest running along the top of the skull where massive chewing muscles would have attached suggested something else. Nicknamed Nutcracker Man for its chompers, the species was dubbed Zinjanthropus boisei (it’s now called Paranthropus boisei because it is clearly a close cousin of P. robustus, a South African species found by Broom).

Until the Zinjanthropus discovery, determining a hominin fossil’s age was largely a guessing game because there was no good way to measure how long ago an ancient fossil had formed. But advances in nuclear physics in the early and mid-20th century led to radioactive dating techniques that allowed age calculations. Using potassium-argon dating, geologists reported in 1961 that Zinjanthropus came from a rock layer about 1.75 million years old. The fossil was three times older than the Leakeys initially suspected. (Later, A. africanus proved to be even older, living about 2 million to 3 million years ago.) The discovery vastly stretched the timescales on which researchers were mapping human evolution.

The surprises didn’t end there. In the early 1960s, the Leakeys’ team recovered fossils of a hominin that lived at roughly the same time as Zinjanthropus but had smaller, more humanlike teeth and a brain notably bigger than that of both Zinjanthropus and Australopithecus. Because of the elevated brain size and details of the hand, the Leakeys argued that this hominin was the one who made the tools at Olduvai Gorge; in 1964, Louis and colleagues placed it in the human genus with the name Homo habilis, or handy man.

The Homo designation was controversial, and to this day paleoanthropologists debate how to classify these fossils. Still, the discoveries at Olduvai Gorge kicked off a paleo-anthropological gold rush in Africa. A 1974 discovery in Ethiopia, for instance, once again expanded the timescale of human evolution. It was one of the most famous discoveries in all of human evolution: the nearly 40 percent complete skeleton of Lucy, known more formally as Australopithecus afarensis, who lived about 3.2 million years ago.

Since then, researchers have shown repeatedly that the hominin fossil record stretches farthest back in Africa. Today, the oldest purported hominins date back some 6 million or 7 million years — to around the time when the ancestors of humans and chimpanzees probably parted ways.

On the origin of our species

Even after it became clear that hominins originated in Africa, it was still uncertain where our species, Homo sapiens, began. By the 1980s, paleoanthropologists had largely settled into two camps. One side claimed that, like the earliest hominins, modern humans came from someplace in Africa. The other side championed a more diffuse start across Africa, Asia and Europe.

That same decade saw researchers increasingly relying on genetics to study human origins. Initially, scientists looked to modern people’s DNA to make inferences about ancient populations. But by the late 1990s, geneticists pulled off a feat straight out of science fiction: decoding DNA preserved in hominin fossils.

For paleoanthropologists, studying ancient DNA has been like astronomers getting a new telescope that sees into deep space with a new wavelength of light. It’s revealing things no one even thought to look for, says paleoanthropologist John Hawks of the University of Wisconsin–Madison. “That is the most powerful thing that genetics has handed us.”

And it’s revealed a truly tangled tale.

A trellis or a candelabra

Long before the rise of genetics, or even the discovery of many hominin fossils, unraveling human origins was a quest to explain how the world’s different races came to be. But after the horrors of World War II, anthropologists started to question the validity of race.

“This was a real moral hinge point in the science,” Hawks says. “It was a realization that viewing things through the perspective of race was creating evils in the world.” And it was scientifically dubious, as genetic evidence has shown that people are all so similar that race is more of a cultural concept than a biological phenomenon. Humans, in fact, are less genetically diverse than chimps.

As race was de-emphasized in the 1940s and ’50s, anthropologists started to think more about the mechanisms of evolution and how populations change over time, a direct influence of the “modern synthesis” that had united Darwinian evolution and genetics.

One influential forerunner to this period was anatomist and anthropologist Franz Weidenreich. After leaving Nazi Germany in the 1930s, he ended up in China studying fossils known as Peking Man (now classified as H. erectus), who lived several hundred thousand years ago. Weidenreich noticed that Peking Man shared certain features, such as shovel-shaped incisor teeth, with some present-day East Asians.

From this observation of apparent regional continuity across time, he concluded there had never been just one real-life Garden of Eden. As he wrote in 1947, “Man has evolved in different parts of the old world.”

Rather than picturing a family tree with one main trunk and branches, he envisioned human evolution as a trellis. Vertical lines represented groups of humans from different geographic regions, with the crisscrossing lines of the lattice representing mating between groups. Such gene flow enabled ancient forms across Africa, Asia and Europe to stay a unified species that gradually evolved into modern humans, with some regional variation maintained.

One consequence of all that mixing: “Pure” races never existed.

But a minority of researchers clung to the idea that race was central to understanding human evolution. In 1962, American anthropologist Carleton Coon transformed Weidenreich’s trellis into a candelabra, trimming away the intersecting lines. He argued that modern races stemmed from a common ancestor, but different lines independently evolved into H. sapiens, with races crossing the “sapiens” boundary at different times. In his view, Science News Letter explained, “the Negro race is at least 200,000 years behind the white race on the ladder of evolution.”

It’s a deeply disturbing statement to type today, and it was rejected by many at the time. Coon published his claims during the height of the U.S. civil rights movement, less than a year before Martin Luther King Jr. stood on the steps of the Lincoln Memorial and shared his dream of racial equality. Advocates of segregation cited the supposed evidence of inferiority to justify their racist agenda. But many experts discounted Coon’s views. It’s an “extreme opinion,” one anthropologist told Science News Letter in 1962, lacking “evidence of any nature to support it.”

Still, Coon’s claims tarnished Weidenreich’s view of human evolution. And in the 1960s and ’70s, interest shifted to much earlier stages of hominin history, many millions of years ago.

Homo sapiens arrives, somehow

In the mid-1980s, anthropologists went back to disentangling the roots of H. sapiens. By then, a basic picture had emerged: Hominins arose in Africa, and H. erectus was the first to venture outside of it, by what we now know was nearly 2 million years ago. In some places, H. erectus persisted for a long time; elsewhere, new groups appeared, such as Neandertals (H. neanderthalensis) in Europe and Asia. At some point, somehow, H. sapiens arrived and its predecessors vanished.

Some of the oldest fossils classified as Homo sapiens still lack some features typical of people today. For instance, a roughly 300,000-year-old skull (top) from Jebel Irhoud in Morocco has a relatively long, flat braincase. Only later does a tall, rounded braincase appear to evolve, as seen in a 195,000-year-old skull (middle, white fills in missing pieces) from Omo Kibish and a 160,000-year-old skull (bottom) from Herto, both in Ethiopia.

That “somehow” became a matter of debate in the 1980s, ’90s and into the 2000s.

Milford Wolpoff, a paleoanthropologist at the University of Michigan in Ann Arbor, and colleagues revived the latticework of Weidenreich’s trellis model in the 1980s. Under this “multiregional” view, it was difficult to draw a clean line between the end of H. erectus and the beginning of H. sapiens. In fact, Wolpoff argued that H. erectus and other seemingly distinct groups should be folded into our species. Through intergroup mating these earlier “archaic” H. sapiens gradually evolved the features of “anatomically modern” humans.

Critics doubted there could have been enough intergroup mating back then to allow a small, globally scattered population to remain as one. Chris Stringer, a paleoanthropologist at the Natural History Museum in London, and colleagues proposed instead that H. sapiens originated in just one place — descending from H. erectus or a subsequent species — and then spread across the world. Along the way, these humans replaced other hominins, including Neandertals.

Both theories were difficult to test. For instance, the single-origin idea predicted that the oldest modern human fossils should all be found in just one region. But there weren’t many well-dated fossils from the relevant time period. And seeing ourselves in the fossil record proved challenging. Researchers disagreed on what features defined modern humans. A globular head? A flat face? Something as banal as a chin? These disagreements meant researchers on both sides could often look at the same fossil data and claim support for their position.

Genetic revolution

By the 1980s, DNA offered a new way to investigate the deep past. In 1987, one genetic study shifted momentum toward the single-origin theory, with Africa as the point of origin.

Researchers at the University of California, Berkeley analyzed mitochondrial DNA from people around the world. Because it’s inherited from mother to child and undergoes no genetic reshuffling, mitochondrial DNA preserves a record of maternal ancestry. African populations showed the greatest genetic diversity. And when the team built a family tree using the genetic data, it had two main branches: One held only African lineages and the other contained lineages from all over the world, including Africa. This pattern suggested the “mother” lineage came from Africa. Based on the estimated rate at which mitochondrial DNA accumulates changes, the team calculated that this African Eve lived about 200,000 years ago.

“Thus,” the team reported in Nature, “we propose that Homo erectus in Asia was replaced without much mixing with the invading Homo sapiens from Africa.”

Like fossils, genetic evidence is open to interpretation. Proponents of multiregional evolution pointed out that the African diversity may not be indicative of greater antiquity but simply a sign that African populations were much larger than other ancient groups. Mitochondrial DNA also isn’t a complete record of the past — given its unusual inheritance, lineages are easily lost over time.

Even with those warnings, the “Out of Africa” model gained followers as genetic evidence piled up. And in the late 1980s, 1990s and early 2000s, new dating techniques and discoveries suggested the earliest H. sapiens fossils came from Africa, at sites in Ethiopia dating to between 195,000 and 160,000 years ago. More recently, scientists linked roughly 300,000-year-old Moroccan fossils to H. sapiens.

A new window into the past opened in 1997. A team led by Svante Pääbo, a geneticist now at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, recovered mitochondrial DNA from a Neandertal fossil. It was so different from any modern human’s DNA that it suggested Neandertals must be a separate species. That was another blow to the multiregional model.

But paleoanthropology is like solving a jigsaw puzzle without all the pieces; any new piece can change the picture. That’s what happened in 2010. When Pääbo and colleagues assembled the Neandertal’s genetic blueprint, or genome, and compared it with modern human DNA, the team came to a startling conclusion: About 1 to 4 percent of DNA in non-Africans today came from Neandertals.

“We were naïve to think that humans just marched out of Africa, killed some Neandertals and populated the world,” archaeologist John Shea of Stony Brook University in New York later told Science News.

That genetic data seemed to support a compromise model between Out of Africa and multiregionalism. Yes, modern humans originated in Africa, the idea went, but once they expanded into new territories, they mated with other hominins. Hints of such hybridization had been reported in the late ’90s, when some researchers claimed an ancient skeleton from Portugal had a mix of Neandertal and human features.

Interbreeding wasn’t the only shock to come in 2010. Pääbo’s group also analyzed DNA from a finger bone found at Siberia’s Denisova Cave. Both Neandertals and modern humans had once lived there, but the DNA didn’t match either group. For the first time, genetics had revealed a new hominin. These Denisovans are still mysterious, known from only a few bits of bone and teeth, but they too interbred with humans. For instance, Denisovan DNA accounts for about 2 to 4 percent of Melanesian people’s genome.

It’s complicated

Over the last decade, as genetic and fossil revelations have painted a more complex picture of human origins, paleoanthropologists have moved beyond both the multiregional and simple Out of Africa scenarios. Rather than a tree with separate branches or a trellis, human evolution was probably more like a braided stream, a concept traced to paleoanthropologist Xinzhi Wu of the Chinese Academy of Sciences in Beijing, who used a river metaphor to describe patterns of human evolution in China. Different human populations may have emerged, with some floating away and petering out and others connecting to varying degrees.

One emerging view suggests that much of early human evolution occurred in Africa, but there was not one place on the continent where H. sapiens was born. Starting at least 300,000 years ago, modern H. sapiens features start to show up in the fossil record. But these features didn’t arise all together. Only through the mating of different populations across Africa did the suite of behavioral and biological traits that define us today crystallize, says Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany.

“Our origins lie in the interactions of these different populations,” she says. Understanding those interactions is limited by how little of ancient Africa researchers have explored so far. Western, central and much of northern Africa are terra incognita.

There’s still much to explore in other parts of the world too. A single, unifying explanation of human origins may not be possible, as different evolutionary processes probably shaped human history in different regions, says Athreya, of Texas A&M University.

Making more progress on understanding those processes and our roots will come from new discoveries, technological advances and, importantly, new perspectives. For the last 100 years, our origin story has been told by mostly white, mostly male scientists. Welcoming a more diverse group of researchers into paleoanthropology, Athreya says, will reveal blind spots and biases as scientists add to and amend the tale.

This is, after all, everyone’s story.

You can lead a cow to a water closet, but can you make it pee there? It turns out that yes, you can.

Researchers in Germany successfully trained cows to use a small, fenced-in area with artificial turf flooring as a bathroom stall. This could allow farms to easily capture and treat cow urine, which often pollutes air, soil and water, researchers report online September 13 in Current Biology. Components of that urine, such as nitrogen and phosphorus, could also be used to make fertilizer (SN: 4/6/21).

The average cow can pee tens of liters per day, and there are some 1 billion cattle worldwide. In barns, cow pee typically mixes with poop on the floor to create a slurry that emits the air pollutant ammonia (SN: 1/4/19). Out in pastures, cow pee can leach into nearby waterways and release the potent greenhouse gas nitrous oxide (SN: 6/9/14).

“I’m always of the mind, how can we get animals to help us in their management?” says Lindsay Matthews, a self-described cow psychologist who studies animal behavior at the University of Auckland in New Zealand. Matthews and colleagues set out to potty train 16 calves, which had the free time to learn a new skill. “They’re not so involved with milking and other systems,” he says. “They’re basically just hanging out, eating a bit of food, socializing and resting.”

Matthews was optimistic about the cows’ potty-training prospects. “I was convinced that we could do it,” he says. Cows “are much, much smarter than people give them credit for.” Each calf got 45 minutes of what the team calls “MooLoo training” per day. At first, the researchers enclosed the calves inside the makeshift bathroom stall and fed the animals a treat every time they peed.

Once the calves made the connection between using the bathroom stall and receiving a treat, the team positioned the calves in a hallway leading to the stall. Whenever animals visited the little cows’ room, they got a treat; whenever calves peed in the hallway, the team spritzed them with water. “We had 11 of the 16 calves [potty trained] within about 10 days,” Matthews says. The remaining cows “are probably trainable too,” he adds. “It’s just that we didn’t have enough time.”

Lindsay Whistance, a livestock researcher at the Organic Research Centre in Cirencester, England, is “not surprised by the results.” With proper training and motivation, “I fully expected cattle to be able to learn this task,” says Whistance, who was not involved in the study. The practicality of potty training cows on a large scale, she says, is another matter.

For MooLoo training to become a widespread practice, “it has to be automated,” Matthews says. “We want to develop automated training systems, automated reward systems.” Those systems are still far from reality, but Matthews and colleagues hope they could have big impacts. If 80 percent of cow pee were collected in latrines, for instance, that could cut associated ammonia emissions in half, previous research suggests.

“It’s those ammonia emissions that are key to the real environmental benefit, as well as potential for reducing water contamination,” says Jason Hill, a biosystems engineer at the University of Minnesota in St. Paul not involved in the work. “Ammonia from cattle is a major contributor to reduced human health,” he says (SN: 1/16/09). So potty training cattle could help create cleaner air — as well as a cleaner, more comfortable living space for cows themselves.

Fuzz
Mary Roach
W.W. Norton & Co., $26.95

Around the world, criminals run free in the forest. These villains can’t be arrested — because they’re not human. In her latest book, Fuzz: When Nature Breaks the Law, Mary Roach puts the spotlight on these miscreants. On the Midway Islands, albatrosses carry out suicide missions against the U.S. Navy’s planes. In Colorado, bears break and enter, raiding the refrigerators of mountain homes. And deer do so much jaywalking.

Nature’s perp list also includes camels, mountain lions, crows and many more. Through such examples, Roach tackles this question: What should we do when animals break laws intended for people?

The book brims with Roach’s irreverent humor, which particularly shines when she experiences human-animal conflict firsthand. She tastes rat bait to better understand its allure and gets training on how to tell if a human body was mauled by a bear or by a human pretending to be a bear. She even engineers a robbery: “I had bananas. I was asking for it. I wanted to know what it was like to be mugged by monkeys.”

But it’s not all fun and reindeer games. Roach highlights how much real pain comes from human-animal interactions. Elephants routinely destroy people’s crops and homes. They, along with leopards, bears, deer and others, can also kill people. She also tackles the ethics of eradicating pests by mass poisoning or altering their genetics.

The stories might seem disparate, but they serve a wider point. Many wildlife strategies seek to save people from wild animals’ unwelcome behavior, or to increase the numbers of animals that people want to shoot, eat or admire. What would happen, Roach wonders, if we thought more about coexistence instead of conflict or exploitation?

Most chapters offer a blend of modern science and history, with Roach’s flair for spotting hidden absurdities. Not all the stories of nature’s criminal intent quite land, however. She highlights, for instance, how falling trees kill people, and how uncooked beans cause significant gastrointestinal distress. But it’s a stretch: Widow-makers and musical fruits are inanimate objects, lacking motive, means or opportunity. It’s hard to feel threatened by a tree or bean that can’t come running after you. Nonetheless, as another entry in Roach’s canon of books, Fuzz stands tall (and hairy), educating as much as it entertains. But please: Just learn from her. Do not taste the rat bait.

Buy Fuzz from Bookshop.org. Science News is a Bookshop.org affiliate and will earn a commission on purchases made from links in this article.

In the next week or so, the sea ice floating atop the Arctic Ocean will shrink to its smallest size this year, as summer-warmed waters eat away at the ice’s submerged edges.

Record lows for sea ice levels will probably not be broken this year, scientists say. In 2020, the ice covered 3.74 million square kilometers of the Arctic at its lowest point, coming nail-bitingly close to an all-time record low. Currently, sea ice is present in just under 5 million square kilometers of Arctic waters, putting it on track to become the 10th-lowest extent of sea ice in the area since satellite record keeping began in 1979. It’s an unexpected finish considering that in early summer, sea ice hit a record low for that time of year.

The surprise comes in part because the best current statistical- and physics-based forecasting tools can closely predict sea ice extent only a few weeks in advance, but the accuracy of long-range forecasts falters. Now, a new tool that uses artificial intelligence to create sea ice forecasts promises to boost their accuracy — and can do the analysis relatively quickly, researchers report August 26 in Nature Communications.

IceNet, a sea ice forecasting system developed by the British Antarctic Survey, or BAS, is “95 percent accurate in forecasting sea ice two months ahead — higher than the leading physics-based model SEAS5 — while running 2,000 times faster,” says Tom Andersson, a data scientist with BAS’s Artificial Intelligence lab. Whereas SEAS5 takes about six hours on a supercomputer to produce a forecast, IceNet can do the same in less than 10 seconds on a laptop. The system also shows a surprising ability to predict anomalous ice events — unusual highs or lows — up to four months in advance, Andersson and his colleagues found.

Tracking sea ice is crucial to keeping tabs on the impacts of climate change. While that’s more of a long game, the advanced notice provided by IceNet could have more immediate benefits, too. For instance, it could give scientists the lead time needed to assess, and plan for, the risks of Arctic fires or wildlife-human conflicts, and it could provide data that Indigenous communities need to make economic and environmental decisions.

Arctic sea ice extent has steadily declined in all seasons since satellite records began in 1979 (SN: 9/25/19). Scientists have been trying to improve sea ice forecasts for decades, but success has proved elusive. “Forecasting sea ice is really hard because sea ice interacts in complex ways with the atmosphere above and ocean below,” Andersson says.

Existing forecast tools put the laws of physics into computer code to predict how sea ice will change in the future. But partly due to uncertainties in the physical systems governing sea ice, these models struggle to produce accurate long-range forecasts.

Using a process called deep learning, Andersson and his colleagues loaded observational sea ice data from 1979 to 2011 and climate simulations covering 1850 to 2100 to train IceNet how to predict the state of future sea ice by processing the data from the past.

To determine the accuracy of its forecasts, the team compared IceNet’s outputs to the observed sea ice extent from 2012 to 2017, and to the forecasts made by SEAS5, the widely cited tool used by the European Centre for Medium-Range Weather Forecasts. IceNet was as much as 2.9 percent more accurate than SEAS5, corresponding to a further 360,000 square kilometers of ocean being correctly labelled as “ice” or “no ice.”

What’s more, in 2012, a sudden crash in summer sea ice extent heralded a new record low extent in September of that year. In running through past data, IceNet saw the dip coming months in advance. SEAS5 had inklings too but its projections that far out were off by a few hundred thousand square kilometers.

“This is a significant step forward in sea ice forecasting, boosting our ability to produce accurate forecasts that were typically not thought possible and run them thousands of times faster,” says Andersson. He believes it’s possible that IceNet has better learned the physical processes that determine the evolution of sea ice from the training data while physics-based models still struggle to understand this information.

“These machine learning techniques have only begun contributing to [forecasting] in the last couple years, and they’ve been doing amazingly well,” says Uma Bhatt, an atmospheric scientist at the University of Alaska Fairbanks Geophysical Institute who was not involved in the new study. She also leads the Sea Ice Prediction Network, a group of multidisciplinary scientists working to improve forecasting.

Bhatt says that good seasonal ice forecasts are important for assessing the risk of Arctic wildfires, which are tied strongly to the presence of sea ice (SN: 6/23/20). “Knowing where the sea ice is going to be in the spring could potentially help you figure out where you’re likely to have fires — in Siberia, for example, as soon as the sea ice moves away from the shore, the land can warm up very quickly and help set the stage for a bad fire season.”

Any improvement in sea ice forecasting can also help economic, safety and environmental planning in northern and Indigenous communities. For example, tens of thousands of walruses haul out on land to rest when the sea ice disappears (SN: 10/2/14). Human disturbances can trigger deadly stampedes and lead to high walrus mortality. With seasonal ice forecasts, biologists can anticipate rapid ice loss and manage haul-out sites in advance by limiting human access to those locations.

Still, limitations remain. At four months of lead time, the system was about 91 percent accurate in predicting the location of September’s ice edge.IceNet, like other forecasting systems, struggles to produce accurate long-range forecasts for late summer due, in part, to what scientists call the “spring predictability barrier.” It’s crucial to know the condition of the sea ice at the start of the spring melting season to be able to forecast end-of-summer conditions.

Another limit is “the fact that the weather is so variable,” says Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colo. Though sea ice seemed primed to set a new annual record low at the start of July, the speed of ice loss ultimately slowed due to cool atmospheric temperatures. “We know that sea ice responds very strongly to summer weather patterns, but we can’t get good weather predictions. Weather predictability is about 10 days in advance.”

A meandering trek taken by light from a remote supernova in the constellation Cetus may help researchers pin down how fast the universe expands — in another couple of decades.

About 10 billion years ago, a star exploded in a far-off galaxy named MRG-M0138. Some of the light from that explosion later encountered a gravitational lens, a cluster of galaxies whose gravity sent the light on multiple diverging paths. In 2016, the supernova appeared in Earth’s sky as three distinct points of light, each marking three different paths the light took to get here.

Now, researchers predict that the supernova will appear again in the late 2030s. The time delay — the longest ever seen from a gravitationally lensed supernova — could provide a more precise estimate for the distance to the supernova’s host galaxy, the team reports September 13 in Nature Astronomy. And that, in turn, may let astronomers refine estimates of the Hubble constant, the parameter that describes how fast the universe expands.

The original three points of light appeared in images from the Hubble Space Telescope. “It was purely an accident,” says astronomer Steve Rodney of the University of South Carolina in Columbia. Three years later, when Hubble reobserved the galaxy, astronomer Gabriel Brammer at the University of Copenhagen discovered that all three points of light had vanished, indicating a supernova.

By calculating how the intervening cluster’s gravity alters the path the supernova’s light rays take, Rodney and his colleagues predict that the supernova will appear again in 2037, give or take a couple of years. Around that time, Hubble may burn up in the atmosphere, so Rodney’s team dubs the supernova “SN Requiem.”

“It’s a requiem for a dying star and a sort of elegy to the Hubble Space Telescope itself,” Rodney says. A fifth point of light, too faint to be seen, may also arrive around 2042, the team calculates.

The predicted 21-year time delay — from 2016 to 2037 — is a record for a supernova. In contrast, the first gravitational lens ever found — twin images of a quasar spotted in 1979  — has a time delay of only 1.1 years (SN: 11/10/1979).

Not everyone agrees with Rodney’s forecast. “It is very difficult to predict what the time delay will be,” says Rudolph Schild, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who was the first to measure the double quasar’s time delay. The distribution of dark matter in the galaxy hosting the supernova and the cluster splitting the supernova’s light is so uncertain, Schild says, that the next image of SN Requiem could come outside the years Rodney’s team has specified.

In any case, when the supernova image does appear, “that would be a phenomenally precise measurement” of the time delay, says Patrick Kelly, an astronomer at the University of Minnesota in Minneapolis who was not involved with the new work. That’s because the uncertainty in the time delay will be tiny compared with the tremendous length of the time delay itself.

That delay, coupled with an accurate description of how light rays weave through the galaxy cluster, could affect the debate over the Hubble constant. Numerically, the Hubble constant is the speed a distant galaxy recedes from us divided by the distance to that galaxy. For a given galaxy with a known speed, a larger estimated distance therefore leads to a lower number for the Hubble constant.

This number was once in dispute by a factor of two. Today the range is much tighter, from 67 to 73 kilometers per second per megaparsec. But that spread still leaves the universe’s age uncertain. The frequently quoted age of 13.8 billion years corresponds to a Hubble constant of 67.4. But if the Hubble constant is higher, then the universe could be about a billion years younger.

The longer it takes for SN Requiem to reappear, the farther from Earth the host galaxy is — which means a lower Hubble constant and an older universe. So if the debate over the Hubble constant persists into the 2030s, the exact date the supernova springs back to life could help resolve the dispute and nail down a fundamental cosmological parameter.

A closeup view of even the most common objects can make the mundane look spectacular.

A glimpse of the underside of a southern live oak tree leaf, which won first place in the 2021 Nikon Small World photomicroscopy competition, is just one example. Jason Kirk, director of Baylor College of Medicine’s Optical Imaging and Vital Microscopy Core in Houston and a self-described microscope enthusiast, snapped the prizewinning photo with a microscope that he finished building in the early days of the coronavirus pandemic. He tested his homemade device with a variety of objects from his yard, including tree leaves.

Tap this image and those below to enlarge

“A lot of times, you stick weird stuff under the microscope and see what it looks like,” Kirk says. “That’s what happened with this.”   

His daughter remarked that the leaf’s trichomes — structures that help protect plants and other organisms from extreme weather and insects — looked like sea anemones. That comment inspired Kirk to craft a photo that made the leaf’s underside look like an underwater landscape.

The picture is a composite of around 200 images stacked together. The leaf’s trichomes are colored white and stick out of cyan-colored vessels, which carry water. Surrounding stomata, colored purple, regulate the flow of gases such as carbon dioxide.

The oak leaf was one of 100 stunning images recognized in this year’s competition, the results of which were announced September 13. Here are a few of our favorites.

A sky full of neurons

It took a month of work for Esmeralda Paric and Holly Stefen, both of Macquarie University in Sydney, to capture this striking scene. Though at first glance it might look like a peek at galaxies, those glowing “stars” are mouse brain cells — part of an experiment that could help researchers understand the mechanisms behind neurogenerative diseases such as dementia.

The image, which earned second place in the competition, shows around 300,000 nerve cells, or neurons, separated by inky black fluid. The researchers coaxed some of the cells to extend spindly structures called axons, which allow neurons to send electrical signals, across the fluid.

“I named [the image] ‘The Jedi and the Sith’ … because when I look at it, I am compelled to reflect on [the] balance and connections that exist between otherwise seemingly isolated or opposing sides,” Paric says.

Her friends, however, had another name for the image. They “lovingly dubbed it ‘The Neuroverse,’” she says.

A menacing louse

Is it a scorpion’s tail? Or perhaps a crab’s claw?

No, this menacing, microscopic snapshot shows a side view of the rear leg and claw of a hog louse (Haematopinus suis). The hog louse lives primarily on swine, where the insect feeds on blood, and is one of the largest sucking lice. Severely infested pigs can go bald.

Retired biology professor Frank Reiser of Nassau Community College in Garden City, N.Y., captured this picture, which won third place, using dark-field microscopy to make the inner workings of the transparent louse clearly visible. The tubes running along the louse are respiratory tubes, called tracheae, carrying oxygen to tissues.  

An embryonic rat’s whirl of nerves

As part of a doctoral thesis project, Paula Díaz Cespedes of Pontificia Universidad Católica de Chile in Santiago, who studies injury-related nerve pain, snapped this stunning picture of nerve cells from a 16-day-old rat embryo. The photograph earned fourth place in the competition.

The colorful whirl is a dorsal root ganglion, a cluster of sensory nerve cells, including ones that detect pain. These clusters are found close to the spinal cord in many animals. The major structural component of the cells is colored green, with supporting cells that keep the neurons alive colored red. The nuclei of cells are blue.

Studying how the dorsal root ganglion changes after a painful injury can help researchers better understand chronic pain, Díaz Cespedes says.

A kaleidoscope of dinosaur bone

This work of art isn’t a stained-glass window. It’s a zoomed-in view of a tiny piece of dinosaur bone.

Geologist Bernardo Cesare of the University of Padua in Italy stitched together 25 images to create the picture. The black blobs are fossil remnants of the bone tissue that hosted a single bone cell. The different colors come from polarized light passing through mineral-filled pores within the sliver of bone. As the light moves through the mineral — called chalcedony, a type of quartz — the thickness and orientation of the crystals in relation to the light emit a rainbow of colors.

The small bone fragment, which was unearthed in Utah, inspired many photos such as this one, Cesare says.     

A sea of villi

Caleb Dawson of the Walter and Eliza Hall Institute of Medical Researcher in Parkville, Australia wants to know how the intestine handles the myriad microbes living there. To do that, he plans to image immune cells in the gut. Those immune cells live among and inside tentacle-like structures called villi, shown in this striking picture of a mouse’s intestine.

Showing the villi in their three-dimensional glory was difficult, Dawson says. The task required compiling thousands of images taken in different positions while scanning intestinal tissue. Dawson added antibodies and dyes to the tissue to make parts of the villi fluoresce blue or green under certain types of light.

The Perseverance rover has captured its first two slices of Mars.

NASA’s latest Mars rover drilled into a flat rock nicknamed Rochette on September 1 and filled a roughly finger-sized tube with stone. The sample is the first ever destined to be sent back to Earth for further study. On September 7, the rover snagged a second sample from the same rock. Both are now stored in airtight tubes inside the rover’s body.

Getting pairs of samples from every rock it drills is “a little bit of an insurance policy,” says deputy project scientist Katie Stack Morgan of NASA’s Jet Propulsion Lab in Pasadena, Calif. It means the rover can drop identical stores of samples in two different places, boosting chances that a future mission will be able to pick up at least one set.

The successful drilling is a comeback story for Perseverance. The rover’s first attempt to take a bit of Mars ended with the sample crumbling to dust, leaving an empty tube (SN: 8/19/21). Scientists think that rock was too soft to hold up to the drill.

Nevertheless, the rover persevered.

“Even though some of its rocks are not, Mars is hard,” said Lori Glaze, director of NASA’s  planetary science division, in a September 10 news briefing.

Rochette is a hard rock that appears to have been less severely eroded by millennia of Martian weather (SN: 7/14/20). (Fun fact: All the rocks Perseverance drills into will get names related to national parks; the region on Mars the rover is now exploring is called Mercantour, so the name Rochette — or “Little Rock”  — comes from a village in France near Mercantour National Park.)

Rover measurements of the rock’s texture and chemistry suggests that it’s made of basalt and may have been part of an ancient lava flow. That’s useful because volcanic rocks preserve their ages well, Stack Morgan says. When scientists on Earth get their hands on the sample, they’ll be able to use the concentrations of certain elements and isotopes to figure out exactly how old the rock is — something that’s never been done for a pristine Martian rock.

Rochette also contains salt minerals that probably formed when the rock interacted with water over long time periods. That could suggest groundwater moving through the Martian subsurface, maybe creating habitable environments within the rocks, Stack Morgan says.

“It really feels like this rich treasure trove of information for when we get this sample back,” Stack Morgan says.

Once a future mission brings the rocks back to Earth, scientists can search inside those salts for tiny fluid bubbles that might be trapped there. “That would give us a glimpse of Jezero crater at the time when it was wet and was able to sustain ancient Martian life,” said planetary scientist Yulia Goreva of JPL at the news briefing.

Scientists will have to be patient, though — the earliest any samples will make it back to Earth is 2031. But it’s still a historic milestone, says planetary scientist Meenakshi Wadhwa of Arizona State University in Tempe.

“These represent the beginning of Mars sample return,” said Wadhwa said at the news briefing. “I’ve dreamed of having samples back from Mars to analyze in my lab since I was a graduate student. We’ve talked about Mars sample return for decades. Now it’s starting to actually feel real.”

Sea life’s chemical senses
Science News, September 18, 1971

For fish and other underwater life, a sensitivity to chemicals plays the same role as the sense of smell does for land animals.… [Researchers] have been studying the subtle ways this delicate fish-communication system can be disrupted by pollutants…. One study examined the effects of kerosene pollution on the behavior of lobsters…. The experiments demonstrate that chemical communication interference takes place at extremely low dilutions.

Update

Chemical pollution — from sewage and agricultural runoff to pharmaceutical waste — muddles aquatic animals’ senses with potentially dire effects, decades of research has shown. A chemical used to treat sewage seems to limit some fish species’ abilities to form schools, making the fish vulnerable to predators (SN: 10/27/07, p. 262). Drug-tainted waters can have a variety of effects on fish, including suppressing their appetites (SN: 12/20/08, p. 15). A plastic chemical also appears to confuse senses: Its scent can lure sea turtles into eating plastic debris (SN: 3/28/20, p. 14).

A wide-eyed snake has made scientists do a double take. The Hispaniolan vineboa, with its large protruding eyes and square snout, is the first boa species to be discovered in the Dominican Republic in more than a century.

Naturalist Miguel Landestoy of the Universidad Autónoma de Santo Domingo in the Dominican Republic and colleagues discovered the snake, Chilabothrus ampelophis, slithering in a patch of mountainous dry forest near the country’s southwestern border with Haiti on the island of Hispaniola. The last time researchers described a new boa species on the island was in 1888.

“The fact that an animal could have gone undetected for so long on this island that has a lot of people on it is pretty remarkable,” says R. Graham Reynolds, a herpetologist at the University of North Carolina Asheville.

What’s more, the Hispaniolan vineboa may be among the smallest boas in the world, Reynolds, Landestoy and colleague Robert Henderson of the Milwaukee Public Museum report August 17 in Breviora. Adult boa species typically reach 2 meters or more in length (SN: 10/13/09). The longest Hispaniolan vineboa that the team found, an adult female, measures less than 1 meter. The shortest, probably a juvenile male, is less than a half meter long.

Compared with the three other boa species found on the island, the Hispaniolan vineboa’s small size, large eyes and dark, zigzag patterned scales tipped off the researchers that they had spotted something new. Genetic analyses and close inspections five different snakes plus one shed skin confirmed the team’s hunch that the Hispaniolan vineboa is a species new to science.

But the species may already be in trouble. All serpents that the team found were within one kilometer of each other. That’s “a little bit alarming in the sense that they might be restricted to a very small area,” Reynolds says. Agricultural activities such as charcoal burning threaten the species’ habitat. The team’s next steps will be to figure out the boa’s true range and how big individuals can get.   

Babies may laugh like some apes a few months after birth before transitioning to chuckling more like human adults, a new study finds.

Laughter links humans to great apes, our evolutionary kin (SN: 6/4/09). Human adults tend to laugh while exhaling (SN: 6/10/15), but chimpanzees and bonobos mainly laugh in two ways. One is like panting, with sound produced on both in and out breaths, and the other has outbursts occurring on exhales, like human adults.

Less is known about how human babies laugh. So Mariska Kret, a cognitive psychologist at Leiden University in the Netherlands, and colleagues scoured the internet for videos with laughing 3- to 18-month-olds, and asked 15 speech sound specialists and thousands of novices to judge the babies’ laughs.

After evaluating dozens of short audio clips, experts and nonexperts alike found that younger infants laughed during inhalation and exhalation, while older infants laughed more on the exhale. That finding suggests that infants’ laughter becomes less apelike with age, the researchers report in the September Biology Letters.

Humans start to laugh around 3 months of age, but early on, “it hasn’t reached its full potential,” Kret says. Both babies’ maturing vocal tracts and their social interactions may influence the development of the sounds, the researchers say.

A second trial in the new study with different audio clips and a new group of 100 novices also found that older infants seemed to laugh mainly on exhales. And participants of both trials reported that the more adultlike laughs were more pleasing to hear and contagious. That second finding suggests that the shift in laughter as infants age may partly happen due to unconscious affirmations from the babies’ parents, Kret says. Laughs during exhalation are clearer and louder than during inhalation, she says, sending a stronger signal during interactions that may be better for bonding.

The idea that social interactions shape human babies’ laughs matches observations from chimpanzees, says Marina Davila Ross, a comparative psychologist at the University of Portsmouth in England who was not part of the new study. Davila Ross has found that among chimpanzees in different social groups, laughs can have somewhat different sounds and social functions. And humans and chimps alike adjust their laughs based on peers’ feedback, she says.

Still, the number of audio clips analyzed in the new study is small, making it difficult to discern trends, says D. Kimbrough Oller, a theoretical biologist at the University of Memphis in Tennessee who wasn’t involved in the research. All together, listeners in the study’s trials heard 108 clips of infants laughing, with each clip lasting four to seven seconds.

And while people may think that babies laugh a lot, Oller says, all-day recordings suggest babies rarely laugh. More often, they’re making other pre-speech sounds: “babbling, squeals, growls, raspberries — babies are producing those all day long.” The intense examples of laughter used in this study that were caught on camera probably aren’t all that representative, he says, so scientists should listen in all day to better understand the range of early laughter.

There’s also much more to laughter than breathing, Davila Ross says. Laughter can take on greater complexity with the vibration of vocal folds and a more melodious sound if vowels are heard.  It’s not clear how these aspects of human infants’ and apes’ laughs compare, she says, and a more thorough analysis would examine the structure of laughs’ sound waves.

Reading into laughter’s pleasantness could also be problematic, says Carolyn McGettigan, a psychologist and cognitive neuroscientist at University College London. What people rate as enjoyable may be tangled up with how they perceive kids’ ages. Individuals may, for example, enjoy older infants’ laughs more if they think toddlers are more fun than young infants.

Still, the research provides a good starting place, she says. “Studying these kinds of infant vocal behaviors gives us this window into the evolution of what we can do with our voices.” 

When smoke rises from wildfires in the western United States, it pummels clouds with tiny airborne particles. What happens next with these clouds has been largely unstudied. But during the 2018 wildfire season, researchers embarked on a series of seven research flights, including over the Pacific Northwest, to help fill this gap.

Using airborne instruments to analyze small cumulus clouds affected by the smoke, the scientists found that these clouds contained, on average, five times as many water droplets as unaffected clouds. That in itself was not a huge surprise; it’s known that organic and inorganic particles in smoke can serve as tiny nuclei for forming droplets (SN: 12/15/20). But the sheer abundance of droplets in the affected clouds astounded the team. 

Counterintuitively, those numerous droplets didn’t make the clouds more likely to produce rain. In fact, the opposite occurred. Because the droplets were about half as big as those found in a typical cloud, they were unlikely to collide and merge with enough other droplets to result in rain. The chances of rain were “virtually zero,” the researchers write in the August Geophysical Research Letters.

The new research suggests that wildfires could lead to clouds producing less rain in the U.S. West, feeding into drought conditions and potentially increasing future wildfire risk.

But the environmental dynamics involved are complex, says Cynthia Twohy. She’s a San Diego–based atmospheric scientist at NorthWest Research Associates, a research organization specializing in geophysical and space sciences headquartered in Redmond, Wash. For instance, Twohy and her colleagues found that “the ratio of light-absorbing to light-scattering particles in the smoke was somewhat lower than measured in many prior studies,” she says.  

“The take-home message is that while other studies have shown wildfire smoke has an absorbing (warming) influence that can be important for cloud formation and development, these impacts may be less in the western U.S., because the smoke is not as dark,” Twohy says. The impact of the lighter smoke is still an open question. “It’s just another way that smoke-cloud interactions are a wild card in the region.”  

The team used onboard probes to sample clouds affected by wildfire smoke and compare them to their more pristine counterparts. The probes measured how many cloud droplets were present in the samples, the size range of those droplets and the liquid water content of the clouds.

A special tube mounted on the exterior of the plane to collect and evaporate cloud droplets was used to “reveal the particles that the droplets were condensed on,” says Robert Yokelson, an atmospheric chemist at the University of Montana in Missoula who was not involved with the research. This process enabled the researchers to confirm what the original smoke particles were made of, a technique that Yokelson calls “neat.”

The analysis detected the amounts of carbon, oxygen, nitrogen, sulfur and potassium found in residual particles evaporated from cloud droplets. These elements were present in similar amounts to those found in smoke particles sampled from below the clouds, “implying that the cloud droplets also formed on smoke particles,” Twohy says.

Previous studies conducted in the Amazon have shown that “smoke will make the cloud droplets smaller and more numerous,” thereby reducing rainfall, Yokelson says. But this study provides robust evidence that the phenomenon isn’t isolated to the Amazon. It echoes the results of a much smaller 1974 study of smoke-filled clouds over the western United States, providing a crucial present-day snapshot of the challenges facing the region.

Wildfires in the western United States have been breaking records in recent years — increasing in number and size due to climate change — a trend that scientists think will get worse as the globe continues to warm (SN: 12/21/20). As a result, Twohy says, it’s increasingly important that researchers continue to monitor these fires’ influence on the atmosphere.

If you’ve ever felt the wrath of a biting or stinging insect, it may seem incredible that something so small can so easily slice or puncture human skin. 

Scientists already knew that some small animals’ piercing and slashing body parts are infused with metals such as zinc and manganese, making the parts tough and durable. Now, a study published September 1 in Scientific Reports shows how these toollike appendages form hard and extremely sharp cutting edges.

Robert Schofield, a physicist at the University of Oregon in Eugene, and colleagues used a special microscope to examine the sharp “teeth” that line the jaws of leaf-cutting ants called Atta cephalotes, revealing the teeth’s atomic structure (SN: 11/24/20). The team found that zinc atoms were dispersed homogeneously, rather than in chunks, throughout a single tooth. This uniformity allows the ants to grow much thinner, sharper blades, since “chunks of mineral limit how sharp the tool can be,” Schofield says.

The team also tested a suite of properties of these metal-infused materials, known as heavy element biomaterials, in ant teeth, spider fangs, scorpion stingers and marine worm jaws, among others. These structures are stiffer and more damage-resistant than biomineralized materials, like the calcium phosphate typically found in teeth or the combination of calcium carbonate and the protein chitin in many arthropod shells, the team found. The metal-fortified body parts have “the kinds of properties that you want in a knife or needle,” Schofield says.

The team estimates that the zinc-infused teeth of A. cephalotes allow it to puncture and cut using only about 60 percent of the energy and muscle mass it would otherwise. 

By making these sharp, precisely sculpted tools, ants and other small animals can make up for their tiny muscles, allowing them to acquire and process foods that would normally be beyond their reach.

Physicist Stephan Reuter of Polytechnique Montréal spends most days using his expertise in energy and matter to improve medical technologies. Recently though, he stood in a sea of green to consider how a shower of charged particles might affect lettuce.

He had been invited to one of the largest commercial greenhouses in Quebec to help the growers rethink the energy of agriculture. Inside the building, encased by glass walls and covering more ground than four soccer fields, thousands upon thousands of lettuce plants floated on polystyrene mats in a hydroponic, or no-soil, growing system. The crop was nearly ready to be picked, packaged and shipped. Reuter’s task was to use physics to help the company, Hydroserre Inc. in Mirabel, reduce its carbon footprint.

To that end, the company is interested in finding new ways to fight pathogens and to deliver fertilizer to the growing plants. Many fertilizers contain ammonia, which is produced from nitrogen (necessary for plant growth) and hydrogen using a chemical reaction called the Haber-Bosch process. This process revolutionized agriculture in the early 20th century by making mass production of fertilizer possible. However, the process yields hundreds of millions of metric tons of carbon dioxide each year.

“Ideally, we want a fertilizer that’s renewable,” Reuter says. And to make it truly green, it should be created at the farm, making transport, another carbon emitter, unnecessary. Reuter and a growing number of chemists, physicists and engineers think they can see how to make that happen. These researchers are working toward future farms that are truly sustainable, where the energy from renewable sources like wind or solar is harnessed to make an efficient fertilizer on-site. They hope to realize this vision by exploiting plasma.

Plasma everywhere

Reuter might seem an unlikely consultant for an agricultural challenge. After all, his expertise is in the physics of plasma, one of the four fundamental states of matter, along with solids, liquids and gases.

Plasma is remarkably common. In fact, most matter seen in the known universe — more than 99.9 percent, according to astrophysicists — is in a plasma state. Lightning produces plasma. So do those inexpensive novelty lamps in museum gift shops. Switch on the power, and an electrode at the sphere’s center produces a high voltage that interacts with the gas sealed inside the glass to form tendrils of colored plasma that radiate outward. Touch the glass, and the plasma tendrils seem to reach toward your fingers.

The sun is a ball of plasma and gas. The solar wind is a stream of plasma that peels off the sun (SN: 12/21/19 & 1/4/20, p. 6). When that wind collides with the protective, plasma-rich magnetic cushion that envelopes Earth, the interactions produce rivers of light seen in the aurora borealis and aurora australis.

Plasma is also a workhorse of modern technology. Engineers use it to etch the millions of tiny transistors found on the chips in today’s computers, cars and musical birthday cards. The pixels in plasma televisions contain gas that forms a plasma, sealed inside tiny cells sandwiched between two glass plates, and neon signs and fluorescent lights glow because of plasma. Some former astronauts even predict that plasma engines will someday propel us to Mars.

But what exactly is plasma? It’s a soup of electrons with their negative charges, positive ions and neutral atoms that also produces electromagnetic fields and ultraviolet and infrared radiation. Plasma comes about when gas gets super energized — by heat or an electric current, for example — and electrons are freed from atoms.

Plasmas occur naturally or can be human-made. When produced by high temperatures, such as in the sun, it’s called “hot plasma,” while the plasma created in a plasma ball and other room-temperature, low-pressure environments is called “cold plasma.” Plasma balls make it easy to see: They’re filled with a gaseous mixture that includes one of the very stable, noble gases, like argon, xenon, neon or krypton. Plasma makes up those glowing tendrils that reach out from the center. The high-frequency current excites electrons that then separate from the atoms of gas. Many agricultural experiments include a mix of noble gases and air to yield ions of nitrogen and oxygen.

Scientists have long been interested in plasma’s biological implications. In the late 19th century, the Finnish physicist Karl Selim Lemström observed that the width of growth rings in fir trees near the Arctic Circle followed the cycle of the aurora borealis, widening when the northern lights were strongest. He hypothesized that the light show somehow encouraged plant growth. To artificially emulate the northern lights, he placed a metal wire net over growing plants and ran a current through it. Under the right conditions, he reported, the treatment produced larger vegetable yields.

For decades, scientists have known that exposure to plasma can safely kill pathogenic bacteria, fungi and viruses. Small studies in animals also suggest that plasma can prompt the growth of blood vessels in skin. In his research, Reuter studies ways to harness these properties to inhibit new infections in wounds and expedite healing or treat other skin conditions. But more recently, he and other physicists have been working on ways to use the power of plasma to improve food production.

Experiments conducted in the last decade or so have tested a mix of ways to apply plasma to seeds, seedlings, crops and fields. These include plasma generated using noble gases, as well as plasma generated from air. In some cases, plasma is directly applied through plasma “jets” that stream over the seeds or plants. Another approach uses plasma-treated water that can do double duty: irrigation and fertilization. Some studies have reported a range of benefits, from helping plants grow faster and bigger to resisting pests.

“Even in this very, very early stage of research that we’re at with plasma, which has really only come into its own in the last 10 to 15 years, we’re seeing very promising data,” says plant pathologist Brendan Niemira at the Food Safety and Intervention Technologies Research unit at the U.S. Department of Agriculture’s Eastern Regional Research Center in Wyndmoor, Pa. He’s a fan of the approach: On Zoom, Niemira’s avatar shows an almond basking in an eerie, purple plasma glow.

The challenge now, he says, is to figure out whether plasma can deliver at the level of hectares of crops. “Can we make it work in a field environment [to] deliver an advantage that can be integrated into grow systems in the future?”

Nested within that challenge are many others, including finding a way to deliver plasma to plants on a large scale, confirming benefits reported in lab studies and showing that plasma is better than current methods. And, finally, figuring out what the charged soup of plasma is actually doing to plants.

Recent advances became possible, Niemira says, largely because in the 1990s and early 2000s, scientists developed efficient and cost-effective ways to generate cold plasmas by streaming high-energy electrons into a gas. Those electrons would collide with gas molecules, knocking off electrons and producing charged particles. Since then, he says, there’s been something of a rush to test plasma on plants at all stages of growth and with a range of strategies.

Surface changes

One of the most appealing uses of plasma, according to Reuter, is as a fertilizer alternative to ammonia. His plan for the Mirabel greenhouse project, which he helped launch in spring 2021 with scientists from the Quebec-based nonprofit IRDA, or Research and Development Institute for the Agri-Environment, goes something like this: The plasma is generated by sending an electric current through a gas that, ideally, is just air. That process creates a mix of charged and neutral particles, including electrons and ions, that can produce reactive species of nitrogen and oxygen. In tabletop experiments and then in the greenhouse, Reuter and his colleagues will enrich water with plasma, then study whether it can reduce pathogens and affect the growing plants.

Reactive species, as the name implies, are ready to react with atoms and molecules, including in living things, and are biologically available to plants. When the plasma is added to the water, those reactive species dissolve. The resulting plasma-infused water, with its biologically available nitrogen, will then be used to irrigate the plants. It will do the same job as ammonia: Nitrogen, which plants require for growth, is delivered as ions, excited molecules and compounds in the water. While heavy doses of reactive species can harm plant cells or DNA, the amount in plasma-treated water has been shown to be safe for the plant, Reuter says.

Experiments led by biochemist Alexander Volkov of Oakwood University in Huntsville, Ala., offer another example of the kind of research going on in plasma agriculture. Volkov studies the ways in which plants and electromagnetism interact. For example, he’s shown how an electric stimulus can trigger the closing mechanism on a Venus flytrap.

Recently, Volkov set out to study how plasma would affect 20 seeds of dragon’s-tongue, a cultivar of the bush bean Phaseolus vulgaris. The experiment was low-tech. He and colleagues balanced the seeds on a plasma ball for one minute each, then incubated the seeds in water for seven hours. Two days later, the scientists found that in plasma-treated seeds, the radicle — the little protrusion of root that makes a seed a seedling — measured 2.7 centimeters, compared with 1.8 centimeters in untreated seeds, a gain of 50 percent. The team reported the results in Functional Plant Biology in February 2021.

Roots emerge 

Biochemist Alexander Volkov and colleagues exposed bush bean seeds to plasma jets, then immersed the seeds in water for a day. Two days later, plasma-treated seeds showed larger radicles, or starter roots. The least growth occurred in untreated seeds. The others received plasma for 30 seconds, one minute, five minutes and 15 minutes (shown below). Using a plasma globe, he got less striking results.

All images: A.G. Volkov et al/Plasma Medicine 2020

Less than a centimeter of extra growth may seem modest, but Volkov was encouraged. The benefit couldn’t have come from the reactive species of nitrogen and oxygen because they can’t exit the glass sphere, but somehow, the treated seeds seemed to take up more water to grow faster.

To investigate that idea, he and colleagues studied the seeds using an atomic force microscope and magnetic resonance imaging, which reveals how tissues take up water. At the micrometer-level view of the atomic force microscope, Volkov saw that exposure had roughed up the surface of the seeds. The images looked like carved mountain ranges. Those ridges gave the water more surface area to glom on to, and more openings through which to soak the inside of the seeds, he hypothesized. MRI images of treated beans showed larger swaths of white — indicating more water inside — than untreated beans.

“When we use the plasma balls or lamps, the water can penetrate easily through the pores and accelerate germination,” he says.

Rocky road

The surface of an untreated bush bean seed, as seen in an atomic force microscope image, is relatively smooth (left). After a one-minute plasma treatment (right), the surface becomes rough and corrugated, which may enable water to better penetrate the seed’s exterior.

Changes in seed surface with plasma treatment

The surface of an untreated bush bean seed, as seen in an atomic force microscope image, is relatively smooth (top). After a one-minute plasma treatment (bottom), the surface becomes rough and corrugated, which may enable water to better penetrate the seed’s exterior.

Changes in seed surface with plasma treatment

Growing evidence

Physicist Nevena Puač of the Institute of Physics Belgrade in Serbia has performed dozens of studies testing plasma on plants and has been working in the field for decades. She says most studies — successful or not — have tested two ideas: plasma as a disinfectant or as a growth instigator.

On the disinfecting front, plasma jet treatments of less than a minute on foods including apples, cherry tomatoes and lettuce can reduce disease-causing bacteria, such as Escherichia coli, Salmonella and Listeria. Some studies have looked at higher exposure times as well: In a 2008 study, five minutes of plasma treatment inactivated 90 percent of pathogenic Aspergillus parasiticus fungi on hazelnuts, peanuts and pistachios.

This is the research branch that Niemira works on as well. In May 2019 in LWT–Food Science and Technology, he and colleagues showed that plasma treatment combined with an existing sanitizer killed 99.9 percent of Listeria on apples in under four minutes. Working alone, the sanitizer achieved comparable results after an hour. The combination works much better than either one could possibly work alone, he says.

Investigations on seed germination and plant growth are similarly promising. Researchers at the Chinese Academy of Sciences in Nanjing exposed soybean seeds to plasma. Seven days after exposure, the roots were up to 27 percent heavier than roots from untreated seeds, the team reported in 2014. The same year, researchers in Romania reported similar gains for radish roots and sprouts.

At last year’s Gaseous Electronics Conference, hosted online by the American Physical Society, researchers from Japan presented results from a study of young seedlings treated directly with plasma and with plasma-treated water in a rice paddy in the Aichi prefecture. Plants treated directly with plasma early in the growth process had up to a 15 percent higher yield than untreated plants. But treating plants late in the growth process lowered the yield. Timing matters, Puač says. So does the application method: In some cases in the experiments in Japan, plasma-treated water actually lowered the yield.

“To my knowledge this was the first study where plants were treated directly,” rather than as seeds or after harvest for disinfection, says engineer Katharina Stapelmann of North Carolina State University in Raleigh, who organized the session.

Studies have connected plasma treatment to a range of benefits, Puač says, from growth rate to yield. But other studies suggest that plasma won’t ever be a one-size-fits-all technology.

Researchers in South Korea reported in the Journal of Physics D: Applied Physics in 2020, for example, that while a six-minute plasma exposure boosted germination rates of barley sprouts, an 18-minute exposure, over three days, produced no benefit in growth and lowered total plant weight. Experimental results published in 2000 looked at the effects of direct plasma jets on peas, corn and radishes and found detrimental effects that varied by the gas used in the plasma. The seeds were exposed for two to 20 minutes, and seeds with prolonged exposure were slower to germinate than untreated seeds.

What the research shows, Reuter says, is that before plasma becomes a staple on farms around the world, scientists need to better understand the myriad ways that the fourth state of matter could affect plants.

For instance, successful outcomes for plants might be due in part to the UV radiation produced by plasma; UV radiation has long been used as a disinfectant. The reactive nitrogen and oxygen species, which can be helpful or harmful to living cells depending on how they’re used, probably help as nutrients and disinfectants, as well. Plasma also produces electric and magnetic fields and infrared and visible light. Their impact on plants also hasn’t been fully explored. Even though researchers know what’s in the plasma, and can see how the plants respond, they don’t have the details mapped out, Volkov says.

Gardens big and small

Projects are under way around the world to test plasma on large scales and in different settings. Dutch scientists working in Uganda have developed portable “reactors” that use plasma to generate fertilizers from the air. They hope this invention can meet the need for fertilizers in places where farmers often can’t get ammonia. Early in 2022, Reuter hopes to report his first results from desktop experiments. The hydroponic growing system at Hydroserre will provide him with the opportunity to refine his method.

With any luck, he says, the project will show a way for future farms to replace ammonia and reduce carbon emissions.

While researchers and growers await those results, citizen scientists, amateur physicists and experimental gardeners have been known to make space in the shed for a plasma ball next to their rakes and shovels, to run their own experiments at home.

Volkov has jumped in. When the pandemic shut down his lab last year, he took his work — and his plasma balls — home. He bathed the vegetable seeds for his garden for a minute in the lamp’s rich, purplish glow, and then planted them.

“It was cucumber, tomatoes, eggplants, cabbage,” he says. A backyard test run isn’t proof of anything, Volkov readily acknowledges, and any gardener can attest that a finicky combination of variables can make or break a garden.

But he did see an astounding harvest last fall. By late October, he was still picking big, ripe tomatoes from the vines grown from plasma-treated seeds, at a time when the plants from untreated seeds have often withered. The cucumbers were bigger and juicier. The cabbages, planted in a friend’s nursery, were heavier and more delicious, he says. “I got a fantastic amount of everything.”

Glossy, velvety chocolate that snaps in the fingers and melts in the mouth is the chocolatier’s dream.

But crafting cocoa confections with this optimal texture is no easy feat. The endeavor, known as tempering, demands carefully warming and cooling liquid chocolate until it crystallizes into its most delectable form. Now, scientists may have found a shortcut: adding a small pinch of fatty molecules called phospholipids, researchers report August 31 in Nature Communications.

With phospholipids, “you can simplify the whole tempering process, making sure you always have the right quality of the chocolate,” says food chemist Alejandro Marangoni of the University of Guelph in Canada.

Curious about what occurs on a molecular level during tempering, Marangoni and colleagues focused on the ingredient that gives chocolate its texture — cocoa butter. While previous tempering research had targeted cocoa butter’s main component, triglycerides, the team set its sights on a different sweet spot: the minor components, which include free fatty acids and phospholipids. Removing these minor components from the cocoa butter and adding them back in one by one allowed the researchers to figure out each component’s role during tempering.

With just a pinch of phospholipids added to the cocoa butter — achieving a weight concentration of 0.1 percent of the chocolate’s total — the mixture rapidly crystallized into the elusive, melt-in-the-mouth texture. The process required a single cooling to 20˚ Celsius rather than multiple heating and cooling cycles as tempering typically demands.

Next, the team increased the phospholipid weight concentration in melted dark chocolate by an extra 0.1 percent, and easily produced high-quality textures again. The result suggests that phospholipids could be used to simplify chocolate tempering.

The hack could help small-scale chocolatiers avoid the complications and expenses associated with tempering machines, Marangoni says. Large-scale manufacturers, on the other hand, would need to figure out how to evenly disperse phospholipids in a large vat of molten chocolate, he says.

A 50-page codex of colorful, complex pictograms that dates to the early 16th century includes the most complete — and one of the oldest — written chronologies of early earthquakes in the Americas.

The Telleriano-Remensis, which was created by an unknown pre-Hispanic civilization, describes 12 separate earthquakes that rocked what’s now Mexico and Central America from 1460 to 1542, researchers report August 25 in Seismological Research Letters. The famous codex was written by specialists called tlacuilos, meaning “those who write painting” in the Nahuatl language spoken by Aztecs and other pre-Hispanic civilizations in the area (SN: 3/13/20).

Using other codices from the region, researchers had previously identified the combination of two pictographs that denotes an earthquake. One shows four helices around a central circle or eye, and stands for ollin, meaning “movement” in Nahuatl. The other pictograph shows one or more rectangular layers filled with dots, and means tlalli, or “earth.” For daytime earthquakes, the eye is open; for nighttime quakes, it’s closed.

Seismologist Gerardo Suárez of the National Autonomous University of Mexico and social anthropologist Virginia García-Acosta of the Center for Research and Higher Studies in Social Anthropology, both in Mexico City, pored over the Telleriano-Remensis. The researchers were looking for representations of quakes, comparing what they found to accounts of quakes in other pre-Hispanic codices and texts written later by Spanish friars.

The Telleriano-Remensis uses a pictorial representation of a 52-year cycle to roughly date the quakes. Years are represented by four signs— tecpatl (knife), calli (house), tochtli (rabbit) and acatl (reed) — arranged in 13 permutations. Those images helped the researchers match some pictorial accounts of quakes, including one in 1507, to later descriptions of the events.

Little more is recounted about the precise locations of these quakes or the damage they caused, although one image suggests that a quake triggered flooding that drowned warriors. Other codices may contain more clues, the researchers say, which could help create a more complete chronology of the quakes that shook this ancient world.