Miles-wide asteroid crater found in Greenland
Scientists have uncovered an impact crater large enough to swallow the District of Columbia buried beneath a half mile of snow and ice in Greenland.
The finding suggests that a giant iron asteroid smashed into what is today a glacier during the last ice age, an era known as the Pleistocene Epoch that started 2.6 million years ago. When it ended only 11,700 years ago, mega-fauna including saber-toothed cats had died out while humanity had inherited the Earth.
“This is the first impact crater found beneath one of our planet’s ice sheets,” said Kurt Kjaer, a geologist at the Center for GeoGenetics at the Natural History Museum of Denmark and lead author of the study, published recently in the journal Science Advances.
For three days in May 2016, his team flew over the crater in a German airplane with ice-penetrating radar, drawing imaginary grid lines across the surface.
John Paden, a radio-glaciologist at the University of Kansas, operated the radar on the flight. Every second, it sent 12,000 radio wave pulses down into the ice, reflecting off the ice layers and allowing the team to measure the thickness, structure and age of the ice sheet.
The aerial survey confirmed there was a huge pit with an elevated, circular rim and uplifting structures in the center, all telltale signs of an impact crater.
The team’s analysis showed that the crater, dubbed Hiawatha, is nearly 1,000 feet deep and 20 miles in diameter, placing it among Earth’s 25 largest impact craters, although much smaller than the 90-mile crater left by the dino-busting Chicxulub impact. Formed by an asteroid or comet 6.2 to 9.3 miles in diameter, Chicxulub is buried beneath the Yucatan Peninsula in Mexico and is thought to have changed the atmosphere so drastically that many plant and animal species — including nonflying dinosaurs — died out.
“Once you start looking for structures beneath the ice that look like an impact crater, Hiawatha sticks out like a sore thumb,” said Joseph MacGregor, a glaciologist at NASA Goddard Space Flight Center in Maryland and a coauthor of the study. — Nicholas St. Fleur
HEAT WAVES AND INSECTS
For years, insect populations have dropped worldwide without a clear explanation. A new paper suggests male infertility is at least one factor behind that decline, as higher-than-usual temperatures take a disproportionate toll on males of some insect species.
After a lab-simulated heat wave, researchers from England’s University of East Anglia found that male flour beetles produced vastly less sperm. But they also found that the damage was not confined to the males. Sperm inside a female’s reproductive tract became less viable and the sons of the males that endured the higher temperature became less fertile, too.
Matt Gage, an evolutionary ecologist who led the work published recently in Nature Communications, said he was surprised by the findings, and by how quickly male fertility plummeted.
It has long been known that heat can affect sperm quality in mammals. “There’s a good reason the testes are outside the body,” noted Gage, adding that this keeps the sperm 6 to 10 degrees cooler than body temperature.
But no one had looked to see whether coldblooded males were also affected, even though most of life on earth is coldblooded, he said. And the flour beetles that Gage studied are used to warm environments, living in places that regularly reach 95 degrees.
His team simulated a heat wave in their lab, raising temperatures by 9 to 12 degrees for five days — roughly equivalent to a temperature spike in England last summer, Gage said.
Sperm production in the flour beetles dropped by half, the study showed. A second heat wave nearly sterilized them.
“We thought they might have hardened to temperature extremes,” Gage said. “We found the opposite.”
Females appeared unaffected. But if they had already been inseminated, their fertility fell by 30 percent after the heat exposure. This suggests that heat affects not just the manufacture of sperm, but also its viability, Gage said.
The sons of the males who endured the heat wave produced 20 percent fewer offspring than unstressed males. Gage said he doesn’t know whether the sperm suffered DNA damage from the heat that could not be repaired, or if changes on top of the DNA — epigenetic changes — affected their sons’ fertility.
— Karen Weintraub
SPIDER ‘MILK’
Nursing is so fundamental to being a mammal that we named ourselves after it. (“Mammalis” translates to “of the breasts.”) But over time, scientists have discovered that other animals also produce nutrient-rich elixirs to feed their young, including flamingos, cockroaches and male emperor penguins.
The latest addition to the cast of organisms that lactate — or something like it — is a species of jumping spider.
Researchers in China have discovered that females of the Toxeus magnus spider secrete a milklike fluid to feed their offspring. The study, published recently in the journal Science, also found the arachnid mothers continue to provide the fluid, which contains about four times as much protein as cow’s milk, well after their spawn had become young adults.
Although the spiders are not using mammary glands to produce the fluid, and hence are “lactating” in name only, the findings should prompt scientists to reconsider what they know about nursing and how it evolved, the researchers said.
Jumping spiders are the single largest group of spiders in the world, with more than 5,000 species and a presence on nearly every continent. The tiny T. magnus, also known as the black ant mimicking jumper, looks like an ant, walks like an ant and even waves its front legs in the air like a pair of antennae.
Looking closer, they found that during the first week, the mother was depositing droplets of fluid from her underside onto the nest that the hatchlings would come and drink. After the first week, the offspring would drink the fluid directly from the mother’s body.
The mother continued to provide the fluid even after her young began leaving the nest to forage at 20 days old. This ceased at 40 days.
— Douglas Quenqua