News and notes about science
AFTER THE DINOSAURS’ DEMISE, MANY MAMMALS SEIZED THE DAY
When the dinosaurs are away, the mammals will play.
That’s the basic idea behind the “nocturnal bottleneck” hypothesis, a concept proposed in 1942 that suggested mammals could have survived in a dinosaur-dominated world only by avoiding the sharptoothed beasts during the day and coming out at night.
Mammalogists have long thought the earliest shared ancestor of all mammals was nocturnal, and now a study published Nov. 6 provides a potential date for when the furry creatures stopped cowering in the shadows and started venturing into the daylight.
The researchers found that the first mammals to be active during both day and night appeared around 65.8 million years ago, just 200,000 years after the extinction event that led to the demise of most dinosaurs. They were most likely the ancestors of even-toed ungulates, like today’s cattle, llamas and hippopotamuses, as well as the cetaceans like whales and dolphins.
“In evolutionary time 200,000 years are hardly anything. It’s almost immediately,” said Roi Maor, a doctoral student at Tel Aviv University in Israel and University College London, and lead author of the paper that appeared in Nature Ecology & Evolution.
They also found the first mammals that were clearly diurnal, or only active during the daytime, appeared about 52.4 million years ago, some 13 million years after the dinosaurs died out. Among these mammals were early monkeys and apes, the ancestors of today’s gorillas, gibbons and humans.
Maor cautioned that his study only showed a correlation, not causation, between when nonavian dinosaurs went extinct and when mammals became daytime creatures. But the finding adds support for the 75-year-old hypothesis describing how our ancestors inherited the day after dinosaurs disappeared. Nicholas St. Fleur
THE COOL BEGINNINGS OF A VOLCANO’S SUPERERUPTION
A supervolcano’s underground ocean of magma is not the seething, red-hot molten lava you might imagine. Instead, it is likely at a low enough temperature to be solid.
That is according to a new analysis of volcanic leftovers from an ancient California supereruption, which shows that the magma melted shortly before the volcano erupted. The findings, published Nov. 6 in Proceedings of the National Academy of Sciences, might help scientists forecast when such volcanoes pose a threat.
The supereruption in question occurred 765,000 years ago, carving a vast volcanic depression that is 20 miles long and 10 miles wide, now known as the Long Valley Caldera near California’s Mammoth Mountain. In the process, it ejected a giant quantity of ash and hot gas over one nightmarish week, enough to leave a layer of debris that spread from the Pacific Ocean to Nebraska.
“It would have completely wiped out everything within 50 kilometers of the caldera,” said Brad Singer, a geologist at the University of Wisconsin in Madison and the study’s co-author. “All the vegetation and biota in that area would have been extinguished.”
Scientists do not expect Long Valley to erupt again, but given enough time another supervolcano will likely scar our planet.
The findings suggest that the supervolcano had to wake up from an extremely cold state, raising questions about how a solid ocean of magma could melt and mobilize so rapidly.
Many think that an injection of fresh magma further below the volcano likely did the trick. Shannon Hall
THE BRIDGE WOBBLES. SO DO YOU. THAT’S WHEN THE TROUBLE STARTS.
A bouncy foot bridge is charming — until it isn’t.
This was the case for Brooklyn’s Squibb Park Bridge in 2014, London’s Millennium Bridge in 2000 and a long list of other bridges throughout history that became worrisomely wobbly when large crowds crossed over them. Authorities temporarily closed the Squibb Park and Millennium bridges and spent millions of dollars on repairs. What gives? Engineers expect all bridges to move a little with cars, people and wind. But when things get dangerous, like during the Millennium Bridge opening, you can blame it on the interactions between moving crowds and bridges, scientists suggest in a study published Nov. 10 in the journal Science Advances.
Movements of bridges and people feed off one another, Igor Belykh, an applied mathematician at Georgia State University, who led the study, explained. You step on a bridge, it moves a little bit; you adjust to steady yourself. And on and on. “However when the bridge starts wobbling significantly, I, as a pedestrian, have to adjust my gait,” he said. And when a critical number of people try to find balance at the same time and their movements sync up, they can align with the sway of the bridge. And that’s when things get scary.
Researchers had attributed the wobbly Millennium Bridge to this phenomenon, which they call phase-locking. The new study confirmed that and challenged a popular belief that the sway gradually grew with crowd size. They found that the wobble starts suddenly, after the crowd exceeds a
critical threshold. For the Millennium Bridge, that was about 165 people.
Belykh and his colleagues described these dynamic relationships using complex mathematical models — which they jokingly call “crash test dummies” — that they hope will become part of industry standards. Using these models, engineers and designers may be able to plug in all the details about a bridge and its potential pedestrians and figure out how big a crowd must get before a bridge starts to wobble.
“Unfortunately, the more I study and know about the bridges, the more uncomfortable I become when I cross,” said Belykh. Joanna Klein
DINOSAURS COULD BE ALIVE TODAY IF THE ASTEROID HAD STRUCK SOMEWHERE ELSE
Dinosaurs reigned supreme for more than 160 million years. Their dynasty came to a cataclysmic close 66 million years ago when an asteroid crashed into the Yucatán Peninsula in Mexico at a site now known as the Chicxulub crater, paving the way for mammals — and eventually humans — to inherit the Earth.
But had the extraterrestrial impact happened nearly anywhere else, like in the ocean or in the middle of most continents, some scientists now say it is possible dinosaurs could have survived annihilation. Only 13 percent of the Earth’s surface harbored the ingredients necessary to turn the cosmic collision into this specific mass extinction event, according to a study published Nov. 9 in the journal Scientific Reports.
“I think dinosaurs could still be alive today,” if the asteroid had landed elsewhere, Kunio Kaiho, a paleontologist from Tohoku University in Japan and lead author on the study, said in an email.
Other researchers questioned their findings.
When the asteroid, which had a diameter about half the length of Manhattan, struck the coast of Mexico, it found a rich source of sulfur and hydrocarbons, or organic deposits like fossil fuels, according to the researchers. Scorching hot temperatures at the impact crater would have ignited the fuel. The combustion would have spewed soot and sulfur into the stratosphere in sufficient quantities to blot out the sun and change the climate, setting into motion the collapse of entire ecosystems and the extinction of three-quarters of all species on Earth.
Kaiho’s co-author Naga Oshima created a model that simulated asteroid impacts that ejected varying amounts of trapped soot from rock. Only areas with the highest amounts of hydrocarbons released enough soot into the stratosphere to cool the climate to catastrophic levels.
Eighty-seven percent of Earth’s surface, places like most of present day India, China, the Amazon and Africa, would not have had high enough concentrations of hydrocarbons to seal the dinosaurs’ fate. But if the asteroid had hit marine coastal areas thriving with algae, which would have included present day Siberia, the Middle East and the eastern coast of North America, the bang would have been about as devastating to the dinosaurs and life on Earth as the Chicxulub impact. Nicholas St. Fleur
A VERY GOOD DOG HUNTS VERY BAD ANTS
Tobias is a Labrador retriever with one job: sniffing out invasive Argentine ants wherever they hide. He’s really good at it, and with his help, a fragile island ecosystem may be spared a repeat inundation by the pests.
Santa Cruz Island is 25 miles off the coast of Southern California, part of Channel Islands National Park. The island’s rich, rugged environment — which includes more than 1,000 kinds of plants and animals, including the bald eagle and the island fox — is threatened by Argentine ants, one of the world’s most successful and wily invasive species.
The ants are nearly impossible to get rid of; it had never been done with an infestation as large as Santa Cruz’s. But Christina Boser, an ecologist who leads the conservancy’s ant eradication project, devised an aerial assault, dropping tiny sugar water beads spiked with diluted poison from helicopters.
The campaign, largely in 2015 and 2016, appears to have killed off the ants. Still, if even one colony has survived, this elaborate effort might have been wasted.
That’s where Tobias comes in. Once he pinpoints the faint pheromone scent left by this particular species of ant — and no other — he will sit down and look at his handler with the excited expectation of a child on Christmas morning. Tobias’ reward is his “wubba,” a soft blue ball.
“We have developed a really special bond,” said Kyren Zimmerman, a handler with the nonprofit Working Dogs for Conservation, headquartered in Bozeman, Montana.
In March, Tobias and Zimmerman underwent weeks of basic Argentine ant training. Then they took a choppy ferry ride to the island and got to work.
By summer’s end, the pair hadn’t found any new ant colonies in all their hiking and bushwhacking — a great sign that the eradication really worked. Jessica Leber
THE CIRCADIAN CLOCK IN YOUR NOSE
When people tell you, “wake up and smell the roses,” they might be giving you bad advice. Your sense of smell may fluctuate in sensitivity over the course of 24 hours, in tune with our circadian clocks, with your nose best able to do its job during the hours before you go to sleep, according to a study published last month.
The work, reported in the journal Chemical Senses, is part of a larger push to explore whether adolescents’ senses of taste and smell influence obesity. Rachel Herz, a sensory researcher at Brown University, and her colleagues designed this study to see if there might be times of day when the sense of smell was more powerful — perhaps making food smell particularly inviting.
For the experiment, 37 adolescents ranging in age from 12 to 15 came into a lab for a very long sleepover party. For nine days, they followed a strict schedule to allow researchers to focus on the circadian clock, which helps control wake and sleep, but also influences other processes in the body, including metabolism.
While more research is needed to test whether the results fully apply to adults, Herz says that as you grow up, the makeup of the smell receptors inside your nose doesn’t seem to change, although there is evidence your body clock may.
The results showed that the children’s noses were most sensitive tended to correspond to the evening, with an average peak of 9 p.m.
Smell was at its lowest ebb, intriguingly, from about 2 a.m. to 10 a.m. Veronique Greenwood