Earthquakes have rocked the planet for eons. Studying the quakes of old could help scientists better understand modern tremors, but tools to do such work are scarce.
Enter zircons. Researchers used the gemstones to home in on the temperatures reached within a fault during earthquakes millions of years ago. The method offers insights into the intensity of long-ago quakes, and could improve understanding of how today’s tremors release energy, the researchers report in the April Geochemistry, Geophysics, Geosystems. “The more we understand about the past, the more we can understand what might happen in the future,” says Emma Armstrong, a thermochronologist at Utah State University in Logan.
Armstrong and colleagues focused on California’s Punchbowl Fault. That now-quiet portion of the larger San Andreas Fault was probably active between 1 million to 10 million years ago, Armstrong says.
Heat from friction is generated in a fault when it slips and triggers an earthquake. Previous analyses of preserved organic material suggested that temperatures within the Punchbowl Fault peaked between 465° Celsius and 1065° C. The researchers suspected that zircons in rocks from the fault could narrow that broad window.
Zircons often contain the radioactive chemical elements uranium and thorium, which decay to helium at a predictable rate (SN: 5/2/22). That helium then builds up in the crystals. But when a zircon is heated past a temperature threshold — the magnitude of which depends on the zircon’s composition — the accumulated helium escapes.
Measuring the amounts of the three elements in zircons from the fault suggests that the most intense earthquake generated temperatures lower than 800° C. That roughly halves the range previously reported. The finding provides clues to the amount of heat released by quakes, something difficult to measure for modern tremors because they often occur at great depths.
Armstrong plans to continue studying zircons, in the hopes of finding more ways to exploit them for details about ancient quakes.
In a large laboratory cage, a male mosquito carries a genetic weapon that could launch the destruction of his species. That loss could also mean the end of the parasite that causes malaria.
The weapon, a self-replicating bit of DNA known as a gene drive, is one of the most anticipated and controversial tools being developed to stop mosquitoes from spreading diseases like malaria to humans.
The gene drive interferes with the insects’ ability to reproduce. It wiped out captive populations of mosquitoes in eight to 12 generations (SN: 10/27/18, p. 6) in a small lab study. In 2021, the technology worked in the large cages in Terni, Italy, too. Within as little as five to 10 years, this gene drive could be ready to test in the wild.
The first experimental release could be rolled out in Burkina Faso, Mali, Ghana or Uganda. In those locations, researchers are working with a nonprofit research consortium called Target Malaria to develop the gene drive carriers along with other genetically engineered mosquitoes to fight malaria.
This research is driven by the idea that every tool available must be used to fight malaria, which sickened close to 241 million people in 2020 and killed 670,000 worldwide, mostly in Africa. Children 5 years old and younger accounted for about 80 percent of the continent’s malaria deaths, the World Health Organization says.
Because of malaria’s huge toll, large investments have been made to fight the disease, yielding preventive drugs, insecticide-treated bed nets and even malaria vaccines — one was recently recommended for use in sub-Saharan Africa (SN: 12/18/21 & 1/1/22, p. 32). These efforts are helping. But mosquitoes are developing resistance to insecticides, and some anti-malaria drugs may no longer work well.
“To go toward zero [cases], we need to have something that is transformational,” says Fredros Okumu, a mosquito biologist and director of science at Ifakara Health Institute in Tanzania. Gene drives might be the transformational answer people are looking for. Researchers are still refining and testing the technology, which was first devised in 2015 (SN: 12/12/15, p. 16). Though other types of genetically altered mosquitoes have been released in Brazil, the United States and elsewhere, those altered genes spread slowly among wild populations (SN Online: 3/9/22). Gene drives could potentially spread to nearly ever member of a species quickly, forever altering the species or wiping it out.
But whether gene drives ever play a role in combating malaria may depend as much on social considerations as on science.
“A technology doesn’t work by technical strength alone. It works because it embeds into a social context,” says Ramya Rajagopalan, a social scientist at the University of California, San Diego. In the past, scientists “developed a technology in the lab, got it all set up and ready to go, and then you go to the stakeholders and say, ‘Hey, we have this great technology, do you want to use it?’ ”
If people reject that sort of offer, as has happened with some genetically modified crops, researchers often think, “If [the public] only knew enough about the technology, they’d be more accepting,” Rajagopalan says. But more often the failure comes because the researchers “don’t include community voices from the outset in the design and the implementation.”
Because of the possibility of forever altering ecosystems, the European Union has already said “no” to using gene drives there. But Africa is where a gene drive might one day help defeat malaria. Researchers are hoping to eventually release gene drives on the continent, but must first get public consensus. To that end, scientists are looking for ways to involve members of the public in research, and learn about local priorities and how to talk about the technology.
Rattling the cage No one is ready to let mosquitoes carrying gene drives out of the lab yet. For now, researchers are doing tests with mosquitoes in captivity to get an idea of whether the technology will work as planned. In the Terni cage trials, scientists used small rooms, setting humidity levels, lighting and other characteristics to mimic some of the conditions the mosquitoes might encounter in the wild.
In cages almost 5 cubic meters big — about the size of a small dressing room — containing hundreds of Anopheles gambiae mosquitoes, scientists added male members of the same species that carried the engineered change to their DNA.
The gene drive used for this experiment is built on the molecular scissors known as CRISPR/Cas9. Male mosquitoes are engineered to carry the gene drive, which consists of instructions for making the DNA-cutting enzyme Cas9 and an RNA that guides the enzyme to the gene to be cut. When an engineered male mates with an unaltered female, Cas9 snips a gene called doublesex inside the fertilized egg. As the egg tries to repair the cut, the gene drive from the father’s doublesex gene is pasted over the copy of the gene inherited from the mother. So the offspring gets two copies of the gene drive, instead of one.
Normally, any particular version of a gene has a 50 percent chance of being passed from parent to offspring. But with the copy-and-paste CRISPR system, gene drive–carrying mosquitoes pass the drive to about 96 percent of male progeny and more than 99 percent of females. With that genetic cheat, the gene drive spreads rapidly through the population. The doublesex gene is essential for the development of female mosquitoes. When the gene doesn’t work, “the mosquito itself doesn’t work,” says Ruth Müller, chief ecologist and entomologist at the Institute of Tropical Medicine in Antwerp, Belgium. The gene drive breaks the gene.
Female offspring that inherit two copies of a broken doublesex gene develop mouthparts and genitalia that are closer to the male form. Those females are sterile, and they cannot bite people with their malformed mouthparts. Unable to bite, those mosquitoes can’t transmit malaria-causing parasites from their bodies to humans.
In those naturelike cages in Terni, when gene drive–carrying mosquitoes were introduced, the populations died out in 245 to 311 days, researchers reported in July 2021 in Nature Communications. In two cages where no gene drive mosquitoes were added, mosquito populations lived normally to the end of the experiment.
This was the first proof that the gene drive might work under almost real-world conditions, says Müller, one of the study’s leaders. But there is still a lot to learn about drives, she says, including how they will affect mosquito populations in the wild, whether they can slow malaria’s spread and importantly, what the impact will be on other creatures in the environment.
Getting those answers will determine the feasibility of moving forward scientifically. They will also play a big role in whether the public agrees to releasing a tool that could intentionally drive a species toward extinction. Considering all possibilities While Müller’s and other Target Malaria science teams based in Africa, Europe and North America refine gene drives, other affiliated and independent groups are mapping out what releasing a gene drive could do to the planet. “Right now there are a lot of theoretical discussions,” Müller says. It’s important to gather data to “fill the debate with more facts” about the real risks and benefits, she says.
At least 46 theoretical harms could arise from the use of gene drives on mosquitoes, researchers reported in March 2021 in Malaria Journal. Those potential downsides include reductions in pollinators and other species directly or indirectly related to the disappearance of the mosquitoes. It’s possible that people could develop allergic reactions to the bite of mosquitoes carrying a single copy of the gene drive, or to fish that eat the altered mosquito larvae. There could be a decline in water quality caused by large numbers of mosquito larvae dying. There’s even a set of scenarios in which malaria cases increase if, for instance, mosquito species that are better malaria spreaders take over in areas where a gene drive has thinned out less-troublesome mosquitoes.
Dreaming up possible nightmare consequences was an exercise intended to tell researchers what they might need to plan for and test before releasing gene drive mosquitoes into the wild. At workshops held in 2016 through 2019 in Ghana, Kenya, Botswana, Gabon and the United States, researchers worked out a chain of events that might lead to each of those potential harms.
The list of 46 possibilities focused on four areas that African leaders said were most important to protect: biodiversity, human and animal health, and water quality. By identifying these hypothetical hazards, researchers can begin calculating the likelihood of a harm happening and how bad it could be, says report coauthor John Connolly, a senior regulatory scientist for Target Malaria who is based at Imperial College London.
“You probably never really finish a risk assessment, but you get a clearer understanding of the risks and uncertainties,” Connolly says. Target Malaria and independent groups hope to answer some questions by examining data collected from the release of genetically altered mosquitoes that don’t carry gene drives.
Studies of biological pest control mechanisms — such as releasing a predator to eradicate an invasive species (remember invasive cane toads in Australia [SN Online: 10/14/14]) — may also provide some clues about how gene drives may spread, says Keith Hayes, who leads a risk assessment team at the Commonwealth Science and Industrial Research Organization’s Data61 in Hobart, Australia.
Some questions may never truly be answered unless gene drives are released. Scientists can experiment and simulate what might happen, but “at some point you have to say, ‘We don’t know everything. We can’t know everything. There may be surprises,’ ” Hayes says. That’s when a decision will need to be made about a release based on what is known about the risks and benefits.
High stakes Even if those evaluations reveal downsides to gene drives, the potential benefits for human health and economics may far outweigh the risks, Müller argues.
“If you have a high burden of malaria, that costs a lot,” Müller says. “Children cannot go to school. People cannot go to work. That should also be considered if you talk about costs.”
Opponents of gene drives say it’s unfair to paint rejection of the unproven, potentially dangerous, technology as dooming children to death from malaria. “We are already not saving those children with measures [that would help] such as improving sanitation and the medical system,” says Mareike Imken, the European coordinator of the Stop Gene Drives campaign. Her organization is calling for a global moratorium on the release of gene drives until there is worldwide consensus on whether they are safe and necessary and how they should be regulated.
“We need the highest possible obstacle to using this high-risk … technology,” Imken says. Allowing gene drives to be tried against malaria would essentially unleash them for use against a wide variety of organisms, with potentially devastating ecological consequences, she says. Instead, the world should invest more in already proven methods of controlling and eradicating malaria.
But there are potential upsides to gene drives that current approaches, such as insecticides, don’t offer. “The stuff we have been doing for years has been intentionally designed to eradicate mosquitoes. It just didn’t do it. We’ve been spraying the hell out of them for years, and in the process killing a lot of other nontarget organisms,” Okumu says.
By replacing insecticides, gene drives might help save insects including bees, butterflies and other pollinators. And gene drives are designed to eliminate only the mosquito species that are dangerous, Okumu says. “Of all the 3,500 species … we need to target one, two, at maximum three of them.”
He’s referring to the handful of species in the Anopheles genus that are mostly responsible for spreading malaria. In Africa, the primary disease carriers are Anopheles gambiae and the look-alikes An. arabiensis, An. coluzzii and An. funestus.
While eradicating malaria is the goal, making mosquitoes extinct is mostly hyperbole, says Tony Nolan, a molecular biologist at the Liverpool School of Tropical Medicine in England.
“Extinction is not a likely outcome, nor even a desirable one. It’s not necessary to make the mosquito extinct to eliminate malaria,” says Nolan, one of the Target Malaria researchers developing gene drives. Geographic isolation may enable the gene drive to eliminate a local population of mosquitoes but nothing further afield. Mutations can arise in the Cas9 or guide RNA, causing the drive to stop working. Or other things might limit its spread.
But what would happen to the environment if a major mosquito species suddenly disappeared? Some researchers are trying to measure the ecological contributions of An. gambiae, including whether males pollinate plants visited for nectar. As of now, the mosquitoes’ biggest known value is as food for predators. Birds, fish and other animals that eat mosquitoes or their larvae usually aren’t picky about which species is for dinner. Only one species of spider is known to prefer Anopheles mosquitoes over other kinds.
Okumu’s experience leads him to think the malaria carriers wouldn’t be missed much. In some parts of eastern Africa, including Okumu’s home village in Tanzania, a combination of factors including prolonged dry seasons and insecticide and bed net use pushed An. gambiae out. “We have not seen — maybe because we didn’t measure [well enough] — any ecological challenges associated with the disappearance of Anopheles gambiae,” he says.
The mix of malaria carriers can vary considerably depending on local conditions. In Burkina Faso in western Africa, for instance, two villages had different mosquito populations: In Bana, to the northwest of the city Bobo-Dioulasso, about 90 percent of mosquitoes were An. coluzzii with An. gambiae making up 9 percent of the catch, researchers reported in 2019 in Malaria Journal. But on the southeastern side of the city, in the village of Pala, An. gambiae dominated, making up about 84 percent of mosquitoes caught. An. arabiensis accounted for about 10 percent, and An. coluzzii was about 6 percent of the catch in Pala.
If An. gambiae disappeared, one of the other species would fill the vacuum, Okumu says. That could be a good thing if the replacements don’t bite people as much or are lousy at spreading malaria. It could also be worse if the balance shifts toward a more voracious people-biter that easily spreads the parasites. Community input Beyond the scientific hurdles, researchers must also get the public on board with releasing the technology. Without public support, even a gene drive that works perfectly could be a no-go.
Not everyone agrees on when and how to get input. Okumu worries that asking the public whether they want gene drives before scientists have answers to some of the most pressing questions could backfire. “I would rather we know the true benefits, the true risks and gain a consensus around it, and then start engaging the communities,” he says.
Waiting until all the answers are in hand is a flawed approach, says Lea Pare Toe, a social scientist at the Institut de Recherche en Sciences de la Santé in Bobo-Dioulasso. “We should listen to [the community] and develop the science together,” says Toe, who works with Target Malaria to engage local people in the research.
At Bana, researchers didn’t start out talking about gene drives, or even genetic modifications, Toe says. First, the team had to clarify the connection between mosquitoes and malaria. They also had to dispel myths, such as eating fatty foods or sweet fruit can cause the disease. After an intensive engagement campaign from 2014 through 2019, researchers found that such false statements were far less accepted, the researchers reported in October 2021 in Malaria Journal. Once people are clear on the causes of malaria, Toe and colleagues introduce the idea of genetics, and how researchers want to alter mosquitoes to combat malaria. People are generally OK with the uncertainty of research, she says. But they want to know more.
Residents pose specific questions about mosquito biology and ask how researchers can possibly work with such small creatures. They often ask whether the genetic alterations that make the mosquitoes sterile will transfer to humans. People “love the details,” Toe says.
Sometimes, creative approaches are needed to get concepts across. For instance, Target Malaria planned a first stage — releasing genetically sterilized male mosquitoes that won’t diminish mosquito populations — to help researchers collect data on how genetically altered mosquitoes stack up to normal ones in the wild.
Before those altered mosquitoes were set free, the organization wanted to ensure that Bana residents had a deep understanding of the project. Local leaders suggested a play. The scientists wrote a script, but the actors, a local storyteller and other community members revised it to improve storytelling. This helped forge an emotional connection with the audience, Toe and colleagues reported April 5 in Humanities and Social Sciences Communications. Meanwhile in Tanzania, although reluctant to move too soon with the public, Okumu and colleagues talked with community leaders and surveyed residents of 10 villages in the southeastern part of the country, where very few people had heard about genetically modifying mosquitoes. The aim of this 2019 effort was to understand community perceptions, rather than ask permission. People were intrigued by the idea of gene drives, but they had concerns about whether the mosquitoes would look and behave differently from local mosquitoes, the team reported in March 2021 in Malaria Journal.
Community members were also skeptical that targeting just one type of mosquito would be enough to reduce malaria transmission or decrease mosquito bites enough to keep communities on board with the project. It would be better, they said, to get rid of all the biting mosquitoes.
In a separate study done in 2019, people in Uganda who were already familiar with gene drives expressed similar concerns. But those participants anticipated problems if the mosquitoes cross national borders into a country opposed to the release, researchers reported in March 2021 in Malaria Journal. Researchers may have to seek permission to release gene drive mosquitoes on a multinational scale, instead of just getting local and national consent.
Gene drives may win hearts and minds because they will first be tried against disease-carrying mosquitoes “that are very, very much not beloved or charismatic or anything,” says developmental geneticist Kimberly Cooper of UC San Diego. “Do you know anyone who has sympathies for the mosquito? It’s probably the most hated animal on the planet.
“But there will always be people who are very concerned about genetically modified organisms and their release into the environment,” even if those organisms are mosquitoes, says Cooper, who is not involved with the malaria gene drive research but is developing a gene drive to use as a research tool in mice (SN Online: 1/23/19).
Still, the attraction of stamping out malaria is powerful. The benefits could be enormous. But whether they outweigh any environmental risks from the technology and whether the public will buy in to this radical approach remains to be seen.
“There are tons of unknowns,” Okumu says. “The question is, should we pursue it? If you ask me, it would be unethical not to.”
It turns out that chicken and rice may have always gone together, from the birds’ initial domestication to tonight’s dinner.
In two new studies, scientists lay out a potential story of chicken’s origins. This poultry tale begins surprisingly recently in rice fields planted by Southeast Asian farmers around 3,500 years ago, zooarchaeologist Joris Peters and colleagues report. From there, the birds were transported westward not as food but as exotic or culturally revered creatures, the team suggests June 6 in the Proceedings of the National Academy of Sciences. “Cereal cultivation may have acted as a catalyst for chicken domestication,” says Peters, of Ludwig Maximilian University of Munich.
The domesticated fowl then arrived in Mediterranean Europe no earlier than around 2,800 years ago, archaeologist Julia Best of Cardiff University in Wales and colleagues report June 6 in Antiquity. The birds appeared in northwest Africa between 1,100 and 800 years ago, the team says.
Researchers have debated where and when chickens (Gallus gallus domesticus) originated for more than 50 years. India’s Indus Valley, northern China and Southeast Asia have all been touted as domestication centers. Proposed dates for chickens’ first appearance have mostly ranged from around 4,000 to 10,500 years ago. A 2020 genetic study of modern chickens suggested that domestication occurred among Southeast Asian red jungle fowl. But DNA analyses, increasingly used to study animal domestication, couldn’t specify when domesticated chickens first appeared (SN: 7/6/17).
Using chicken remains previously excavated at more than 600 sites in 89 countries, Peters’ group determined whether the chicken bones had been found where they were originally buried by soil or, instead, had moved downward into older sediment over time and thus were younger than previously assumed.
After establishing the timing of chickens’ appearances at various sites, the researchers used historical references to chickens and data on subsistence strategies in each society to develop a scenario of the animals’ domestication and spread.
The new story begins in Southeast Asian rice fields. The earliest known chicken remains come from Ban Non Wat, a dry rice–farming site in central Thailand that roughly dates to between 1650 B.C. and 1250 B.C. Dry rice farmers plant the crop on upland soil soaked by seasonal rains rather than in flooded fields or paddies. That would have made rice grains at Ban Non Wat fair game for avian ancestors of chickens.
These fields attracted hungry wild birds called red jungle fowl. Red jungle fowl increasingly fed on rice grains, and probably grains of another cereal crop called millet, grown by regional farmers, Peters’ group speculates. A cultivated familiarity with people launched chicken domestication by around 3,500 years ago, the researchers say.
Chickens did not arrive in central China, South Asia or Mesopotamian society in what’s now Iran and Iraq until nearly 3,000 years ago, the team estimates.
Peters and colleagues have for the first time assembled available evidence “into a fully coherent and plausible explanation of not only where and when, but also how and why chicken domestication happened,” says archaeologist Keith Dobney of the University of Sydney who did not participate in the new research.
But the new insights into chickens don’t end there. Using radiocarbon dating, Best’s group determined that 23 chicken bones from 16 sites in Eurasia and Africa were generally younger, in some cases by several thousand years, than previously thought. These bones had apparently settled into lower sediment layers over time, where they were found with items made by earlier human cultures. Archaeological evidence indicates that chickens and rice cultivation spread across Asia and Africa in tandem, Peters’ group says. But rather than eating early chickens, people may have viewed them as special or sacred creatures. At Ban Non Wat and other early Southeast Asian sites, partial or whole skeletons of adult chickens were placed in human graves. That behavior suggests chickens enjoyed some sort of social or cultural significance, Peters says.
In Europe, several of the earliest chickens were buried alone or in human graves and show no signs of having been butchered.
The expansion of the Roman Empire around 2,000 years ago prompted more widespread consumption of chicken and eggs, Best and colleagues say. In England, chickens were not eaten regularly until around 1,700 years ago, primarily at Roman-influenced urban and military sites. Overall, about 700 to 800 years elapsed between the introduction of chickens in England and their acceptance as food, the researchers conclude. Similar lag times may have occurred at other sites where the birds were introduced.
Human language, in its many current forms, may owe an evolutionary debt to our distant ape ancestors who sounded off in groups of scattered individuals.
Wild orangutans’ social worlds mold how they communicate vocally, much as local communities shape the way people speak, researchers report March 21 in Nature Ecology & Evolution. This finding suggests that social forces began engineering an expanding inventory of communication sounds among ancient ancestors of apes and humans, laying a foundation for the evolution of language, say evolutionary psychologist Adriano Lameira, of the University of Warwick in England, and his colleagues.
Lameira’s group recorded predator-warning calls known as “kiss-squeaks” — which typically involve drawing in breath through pursed lips — of 76 orangutans from six populations living on the islands of Borneo and Sumatra, where they face survival threats (SN: 2/15/18). The team tracked the animals and estimated their population densities from 2005 through 2010, with at least five consecutive months of observations and recordings in each population. Analyses of recordings then revealed how much individuals’ kiss-squeaks changed or remained the same over time. Orangutans in high-density populations, which up the odds of frequent social encounters, concoct many variations of kiss-squeaks, the researchers report. Novel reworkings of kiss-squeaks usually get modified further by other orangutans or drop out of use in crowded settings, they say.
In spread-out populations that reduce social mingling, these apes produce relatively few kiss-squeak variants, Lameira’s group finds. But occasional kiss-squeak tweaks tend to catch on in their original form in dispersed groups, leading to larger call repertoires than in high-density populations.
Low-density orangutan groups — featuring small clusters of animals that occasionally cross paths — might mirror the social settings of human ancestors. Ancient apes and hominids also lived in dispersed groups that could have bred a growing number of ways to communicate vocally, the researchers suspect.
It was the mid-1980s, at a meeting in Switzerland, when Wally Broecker’s ears perked up. Scientist Hans Oeschger was describing an ice core drilled at a military radar station in southern Greenland. Layer by layer, the 2-kilometer-long core revealed what the climate there was like thousands of years ago. Climate shifts, inferred from the amounts of carbon dioxide and of a form of oxygen in the core, played out surprisingly quickly — within just a few decades. It seemed almost too fast to be true.
Broecker returned home, to Columbia University’s Lamont-Doherty Earth Observatory, and began wondering what could cause such dramatic shifts. Some of Oeschger’s data turned out to be incorrect, but the seed they planted in Broecker’s mind flowered — and ultimately changed the way scientists think about past and future climate.
A geochemist who studied the oceans, Broecker proposed that the shutdown of a major ocean circulation pattern, which he named the great ocean conveyor, could cause the North Atlantic climate to change abruptly. In the past, he argued, melting ice sheets released huge pulses of water into the North Atlantic, turning the water fresher and halting circulation patterns that rely on salty water. The result: a sudden atmospheric cooling that plunged the region, including Greenland, into a big chill. (In the 2004 movie The Day After Tomorrow, an overly dramatized oceanic shutdown coats the Statue of Liberty in ice.) It was a leap of insight unprecedented for the time, when most researchers had yet to accept that climate could shift abruptly, much less ponder what might cause such shifts.
Broecker not only explained the changes seen in the Greenland ice core, he also went on to found a new field. He prodded, cajoled and brought together other scientists to study the entire climate system and how it could shift on a dime. “He was a really big thinker,” says Dorothy Peteet, a paleoclimatologist at NASA’s Goddard Institute for Space Studies in New York City who worked with Broecker for decades. “It was just his genuine curiosity about how the world worked.”
Broecker was born in 1931 into a fundamentalist family who believed the Earth was 6,000 years old, so he was not an obvious candidate to become a pathbreaking geoscientist. Because of his dyslexia, he relied on conversations and visual aids to soak up information. Throughout his life, he did not use computers, a linchpin of modern science, yet became an expert in radiocarbon dating. And, contrary to the siloing common in the sciences, he worked expansively to understand the oceans, the atmosphere, the land, and thus the entire Earth system.
By the 1970s, scientists knew that humans were pouring excess carbon dioxide into the atmosphere, through burning fossil fuels and cutting down carbon-storing forests, and that those changes were tinkering with Earth’s natural thermostat. Scientists knew that climate had changed in the past; geologic evidence over billions of years revealed hot or dry, cold or wet periods. But many scientists focused on long-term climate changes, paced by shifts in the way Earth rotates on its axis and circles the sun — both of which change the amount of sunlight the planet receives. A highly influential 1976 paper referred to these orbital shifts as the “pacemaker of the ice ages.”
Ice cores from Antarctica and Greenland changed the game. In 1969, Willi Dansgaard of the University of Copenhagen and colleagues reported results from a Greenland ice core covering the last 100,000 years. They found large, rapid fluctuations in oxygen-18 that suggested wild temperature swings. Climate could oscillate quickly, it seemed — but it took another Greenland ice core and more than a decade before Broecker had the idea that the shutdown of the great ocean conveyor system could be to blame. Broecker proposed that such a shutdown was responsible for a known cold snap that started around 12,900 years ago. As the Earth began to emerge from its orbitally influenced ice age, water melted off the northern ice sheets and washed into the North Atlantic. Ocean circulation halted, plunging Europe into a sudden chill, he said. The period, which lasted just over a millennium, is known as the Younger Dryas after an Arctic flower that thrived during the cold snap. It was the last hurrah of the last ice age.
Evidence that an ocean conveyor shutdown could cause dramatic climate shifts soon piled up in Broecker’s favor. For instance, Peteet found evidence of rapid Younger Dryas cooling in bogs near New York City — thus establishing that the cooling was not just a European phenomenon but also extended to the other side of the Atlantic. Changes were real, widespread and fast.
By the late 1980s and early ’90s, there was enough evidence supporting abrupt climate change that two major projects — one European, one American — began to drill a pair of fresh cores into the Greenland ice sheet. Richard Alley, a geoscientist at Penn State, remembers working through the layers and documenting small climatic changes over thousands of years. “Then we hit the end of the Younger Dryas and it was like falling off a cliff,” he says. It was “a huge change after many small changes,” he says. “Breathtaking.” The new Greenland cores cemented scientific recognition of abrupt climate change. Though the shutdown of the ocean conveyor could not explain all abrupt climate changes that had ever occurred, it showed how a single physical mechanism could trigger major planet-wide disruptions. It also opened discussions about how rapidly climate might change in the future.
Broecker, who died in 2019, spent his last decades exploring abrupt shifts that are already happening. He worked, for example, with billionaire Gary Comer, who during a yacht trip in 2001 was shocked by the shrinking of Arctic sea ice, to brainstorm new directions for climate research and climate solutions.
Broecker knew more than almost anyone about what might be coming. He often described Earth’s climate system as an angry beast that humans are poking with sticks. And one of his most famous papers was titled “Climatic change: Are we on the brink of a pronounced global warming?”
You can never have too much ice cream, but you can have too much ice in your ice cream. Adding plant-based nanocrystals to the frozen treat could help solve that problem, researchers reported March 20 at the American Chemical Society spring meeting in San Diego.
Ice cream contains tiny ice crystals that grow bigger when natural temperature fluctuations in the freezer cause them to melt and recrystallize. Stabilizers in ice cream — typically guar gum or locust bean gum — help inhibit crystal growth, but don’t completely stop it. And once ice crystals hit 50 micrometers in diameter, ice cream takes on an unpleasant, coarse, grainy texture.
Cellulose nanocrystals, or CNCs, which are derived from wood pulp, have properties similar to the gums, says Tao Wu, a food scientist at the University of Tennessee in Knoxville. They also share similarities with antifreeze proteins, produced by some animals to help them survive subzero temperatures. Antifreeze proteins work by binding to the surface of ice crystals, inhibiting growth more effectively than gums — but they are also extremely expensive. CNCs might work similarly to antifreeze proteins but at a fraction of the cost, Wu and his colleagues thought.
An experiment with a sucrose solution — a simplified ice cream proxy — and CNCs showed that after 24 hours, the ice crystals completely stopped growing. A week later, the ice crystals remained at 25 micrometers, well beneath the threshold of ice crystal crunchiness. In a similar experiment with guar gum, ice crystals grew to 50 micrometers in just three days. “That by itself suggests that nanocrystals are a lot more potent than the gums,” says Richard Hartel, a food engineer at the University of Wisconsin–Madison, who was not involved in the research. If CNCs do function the same way as antifreeze proteins, they’re a promising alternative to current stabilizers, he says. But that still needs to be proven.
Until that happens, you continue to have a good excuse to eat your ice cream quickly: You wouldn’t want large ice crystals to form, after all.